GB2444271A

GB2444271A - Thermostat for an engine cooling system

Info

Publication number: GB2444271A
Application number: GB0623723A
Authority: GB
Inventors: John Moffat
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-11-29
Filing date: 2006-11-29
Publication date: 2008-06-04
Anticipated expiration: 2026-11-29
Also published as: GB2444271B; GB0623723D0; DE102007056949B4; CN101191435B; JP2008138673A; DE102007056949A1; CN101191435A

Abstract

A thermostat assembly includes first and second chambers 110, 111 separated by a thermally conductive dividing wall 115. A temperature responsive valve assembly 220 is located in the second chamber to control the flow from an inlet 117 to an outlet. The temperature responsive valve assembly 220 includes a temperature responsive actuator 222 thermally connected to the dividing wall 115 so that its operation is based not only on the temperature of the coolant in the second chamber 111 but also on the temperature of the coolant in the first chamber 110.

Description

A Thermostat for an Engine Cooling System This invention relates to a

cooling system for an internal combustion engine arid in particular to a thermostat for use in such a cooling system.

It is known that the positioning of a thermostat in an engine cooling circuit or system is a compromise between the respective issues resulting from either outlet or inlet control.

Outlet controlled thermostats, as often used for diesel engines, enable fast engine warm-up but respond slowly to changes in bulk engine coolant temperature. This type of thermostat will often result in large swings in coolant temperature as the engine warms to its normal running temperature. Such large swings in temperature can lead to high thermal stresses in the engine and are undesirable if used for an all aluminium engine which are prone to thermal fatigue.

Inlet controlled thermostats on the other hand have a quick response to bulk engine coolant temperature and are often used in modern gasoline engines which are typically all-aluminium. Unfortunately, inlet controlled thermostats require a fully pressurised radiator circuit when the thermostat is closed and can produce slow engine warm-up times due to the inclusion of additional fluid in the circuit. Slow engine warm-up is undesirable as it can lead to reduced fuel economy and passenger discomfort in cold climates.

It is an object of this invention to provide an improved thermostat assembly for a cooling system of an engine.

According to a first aspect of the invention there is provided a thermostat assembly for a cooling system of an engine comprising a first chamber having an inlet and an outlet, a second chamber having an inlet and an outlet and a temperature controlled valve assembly having a valve member moveable by a temperature responsive actuator located in the second chamber to control the flow of coolant from the inlet to the outlet of the first chamber wherein the second chamber is separated from the first chamber by a thermally conductive dividing wall and the temperature responsive actuator is thermally connected to the dividing wall such that the opening an closing of the valve member is based upon a combination of the temperature of the coolant in the first chamber and the temperature of the coolant in the second chamber.

The inlet to the first chamber may be connected to a return from a radiator forming part of the cooling system and the outlet may be connected to a supply to the engine and the inlet to the second chamber may be connected to a return from the engine and the outlet may be connected to an inlet of the radiator.

The supply to the engine may be an inlet of a circulation pump used to circulate coolant through the cooling system.

The temperature responsive actuator may be thermally connected to the dividing wall by being located in close proximity thereto.

Alternatively, the temperature responsive actuator may be thermally connected the dividing wall by being attached to the dividing wall.

The temperature responsive actuator may have an end face in contact with the dividing wall.

The dividing wall may include a recess and an end portion of the temperature responsive actuator may be fitted in the recess.

The temperature responsive actuator may be thermally connected to the dividing wall by having a least a portion located in coolant cooled by the dividing wall.

The dividing wall may have a tubular portion extending into the second chamber in which an end portion of the temperature responsive actuator may be located.

The tubular portion may define in combination with the end portion of the temperature responsive actuator an annular chamber in which the coolant is cooled by the dividing wall.

The assembly may further comprise a tubular member attached to the tubular wall and the temperature responsive actuator may be located within the tubular member so that an annular chamber is defined between the annular member and the temperature responsive actuator in which the temperature of the coolant is based upon a combination of the temperature of the coolant in the second chamber and the temperature of the dividing wall.

The annular member may have a number of apertures therein to permit the coolant in the second chamber to flow into the annular chamber.

According to a second aspect of the invention there is provided an engine cooling system having a thermostat assembly according to said first aspect of the invention.

The engine cooling system may be a cooling system of a motor vehicle and the cooling system may further comprise a cabin heater having an inlet connected to the cooling system at a position upstream from the temperature controlled valve assembly and an outlet connected to the first chamber.

The inlet to the cabin heater may be connected to the second chamber.

The invention will now he described by way of example with reference to the accompanying drawing of which:-0

Fig.l is a schematic diagram of a prior art outlet

controlled cooling system for an engine;

Fig.2 is a schematic diagram of a prior art inlet

controlled cooling system for an engine; Fig.3 is a graph of temperature against time for the cooling system shown in Fig.l; Fig.4 is a graph of temperature against time for the cooling system shown in Fig.2; Fig.5 is a schematic diagram of a cooling system for an engine according to one aspect of the invention; Fig.6 is a schematic cross-section through a thermostat assembly having a thermally conductive dividing wall and a temperature controlled valve assembly according to another aspect of the invention thermally connected to a dividing wall; Fig.7 is a scrap pictorial view showing a second arrangement for attaching the temperature controlled valve assembly to the conductive dividing wall so as to thermally connect the temperature controlled valve assembly to the dividing wall; Fig.8 is a cross-section through the dividing wall shown in Fig.7; Fig.9 is a cross-section through part of a thermostat assembly having a dividing wall showing a third arrangement for attaching the temperature controlled valve assembly to the conductive dividing wall so as to thermally connect the temperature controlled valve assembly to the dividing wall; Fig.lO is a cross-section through part of a thermostat assembly having a dividing wall showing a fourth arrangement for attaching the temperature controlled valve assembly to the conductive dividing wall so as to thermally connect the temperature controlled valve assembly to the dividing wall; Fig.ll is a cross-section through part of a thermostat assembly having a dividing wall showing a fifth arrangement for attaching the temperature controlled valve assembly to the conductive dividing wall so as to thermally connect the temperature controlled valve assembly to the dividing wall; and Fig.l2 is a cross-section through part of a thermostat assembly having a dividing wall showing an alternative temperature controlled valve assembly thermally connected to the conductive dividing wall.

With reference to Figs.l and 3 there is shown a prior art cooling system of the outlet controlled type fitted to an engine 1.

The cooling system comprises of a circulation pump 2 to circulate coolant through the engine 1 and cooling system, a thermostat 3 controlled by the temperature of the coolant exiting the engine 1, a heat exchanger in the form of a radiator 4, a gas aspirator in the form of a degas bottle 5 and a cabin heater 6.

Coolant flows from the thermostat 3 to the radiator 4 s through a top hose TI-I and flows from the radiator 4 to the pump 2 through a bottom hose BH when the thermostat is open.

When the engine 1 is cold and the thermostat 3 is closed coolant flows through a bypass line BL connecting the thermostat 3 to the pump 2 so as to maintain sufficient flow io through the cylinder head. When the thermostat 3 is closed no coolant flows through the degas bottle 5 and so there is no leakage of cold water from the radiator 4 to the engine 1.

As previously mentioned and shown in Fig.3, the engine 1 warms up quickly with this arrangement. However, during warm-up, when the temperature of the coolant reaches a certain temperature, the thermostat 3 will act in an unstable manner causing the temperature of the coolant at the exit of the engine 1 to swing or oscillate wildly. This is because as soon as the thermostat opens cold coolant will flow from the radiator 4 to the engine 1 causing the temperature of the coolant exiting the engine 1 to drop which causes the thermostat 3 to close. This cycle of opening and closing will continue until the temperature of the coolant from the radiator 4 has risen sufficiently that it does not result in closure of the thermostat 3 when the thermostat is opened.

With reference to Figs 2 and 4 there is shown a prior art cooling system of the inlet controlled type fitted to the engine 1.

As before, the cooling system comprises of the circulation pump 2 to circulate coolant through the engine 1 and cooling system, the radiator 4, the degas bottle 5, the cabin heater 6 and a thermostat 3 controlled by the temperature of the coolant entering the engine 1.

Coolant flows from the engine 1 to the radiator 4 through a top hose TH and flows from the radiator 4 to the thermostat 3 through a bottom hose BE. When the thermostat 3 is open coolant flows from Jt to the pump 2 through a supply line SL and when the thermostat 3 is closed coolant flows from the engine 1 through the radiator 4 and degas bottle 5 to the pump 2.

This flow of coolant through the radiator 4 and degas bottle 5 when the thermostat 3 is closed slows warm-up of the engine 1 due to the additional coolant volume (thermal mass) contained in the circuit relative to the outlet thermostat design..

However, unlike an outlet controlled type there are no great swings in temperature when the thermostat 3 begins to open because it is controlled by the temperature of the coolant leaving the radiator 4 and so will not open fully until the bulk temperature of the coolant has increased sufficiently thereby resulting in only a small ripple in the temperature of the coolant as the relatively small flow of coolant from the radiator 4 mixes with warmed coolant flowing through the engine 1(See Fig.4) With reference to Figs.5 and 6 there is shown a cooling system having a dual flow thermostat assembly 103 according to the invention fitted to an engine 101.

The cooling system comprises of a circulation pump 102 to circulate coolant through the engine 101 and cooling system, a heat exchanger in the form of a radiator 104, a gas aspirator in the form of a degas bottle 105 and a cabin heater 106.

The thermostat 103 is controlled by a combination of the temperature of the coolant exiting the engine 1 through an engine return flow path ER and the temperature of the coolant from the radiator 104 entering the thermostat 103 through a bottom hose BH which connects the thermostat 103 to a return flow from the radiator 104.

When the thermostat is open, coolant flows from the thermostat 103 to the radiator 104 through a top hose TH and flows from the radiator 104 to the degas bottle 105 through a degas line DL and returns to the thermostat 103 through a degas return line DR, which in this case, is connected to the bottom hose BR.

is The thermostat 103 is also connected to the pump 102 by a pump supply line PS and is connected to the cabin heater 106 by a heater supply line HS and a heater return line HR.

As best seen in Fig.6, the thermostat 103 comprises of first and second chambers 110, 111 separated by a thermally conductive dividing wall 115.

The first chamber 110 has a first inlet 112 connected to the return flow from the radiator 104 by the bottom hose BH, a second inlet 113 connected to the return flow from the cabin heater 106 by the heater return line HR and an outlet 114 connected to an inlet of the pump 102 by the pump supply line PS.

The second chamber 111 has a first outlet 116 connected to the cabin heater 106 by the heater supply line HS, a second outlet 118 connected to an inlet of the radiator 104 by the top hose TH and an inlet 117 connected to the return flow ER from the engine 101.

A temperature controlled valve assembly 120 is located in the second chamber 111 to control the flow of coolant from the engine 101 to the radiator 104.

The temperature controlled valve assembly 120 comprises of a valve member 121 which is moveable between open and closed positions by a temperature responsive actuator 122.

A jiggle pin 130 is fitted to the valve member 121 to permit bleeding of air from the system when the valve member 121 is lo in the closed position. A rod 123 connects the valve member 121 to the temperature responsive actuator 122 and a spring is used to bias the valve member 121 into a closed position.

The temperature responsive actuator 122 comprises of a body in which is located a wax element (not shown) that expands when heated so as to urge the valve member 121 open against the action of the spring 125.

The temperature responsive actuator 122 is thermally connected to the dividing wall 115 and, in this case, an end face of the body of the temperature responsive actuator 122 is fastened directly to the dividing wall 115 so as to form the thermal connection.

Operation of the dual flow thermostat assembly is as follows.

When the engine 101 is started from cold the temperature of the coolant throughout the cooling system will be substantially at ambient temperature and the valve member 121 will be in the closed position preventing the flow of coolant from the engine 101 to the radiator 104. it will be appreciated that coolant can however flow from the engine 101 to the cabin heater 106 as this flow is not controlled by the valve member 121. ( -

-10 -Therefore upon start-up from cold, coolant will flow from the engine 101 to the second chamber 111 of the thermostat assembly 103, through the cabin heater 106 via the heater supply and return lines HS and HR back to the first chamber 110 of the thermostat assembly 103 and then from the first chamber 110 of the thermostat assembly 103 to the circulation pump 102 via the pump supply line PS.

During this phase of operation the temperature of the o coolant in the first chamber 110 will be lower than the temperature of the coolant in the second chamber 111 due to the cooling effect of the cabin heater 106 and the volume of static, cold coolant within the bottom hose. Because the temperature responsive actuator 122 is thermally connected to the dividing wall 115 its operation is not determined solely upon the temperature of the coolant flowing from the engine 101 but is based upon a combination of the respective temperatures of the coolant entering the second chamber 111 from the engine 101 through the inlet 117 and the temperature of the coolant entering the first chamber through the second inlet 113 from the cabin heater 106.

The effect of this is that the temperature of the wax element will increase more slowly than if the temperature responsive actuator 122 is exposed only to the coolant from the engine 101 and this will delay opening of the valve member 121 even though the engine 101 is warming up rapidly.

When the combined effect of the coolant passing through the second chamber 111 and the cooling effect on the wax element by its thermal connection to the coolant in the first chamber 110 is such that the force produced by its expansion is able to overcome the action of the spring 125 then the valve member 121 will open. Coolant can then flow to the radiator 104 through the top hose TH from the second chamber 111 and will be returned to the first chamber 110 through the bottom hose BH.

-11 -The coolant returning from the radiator 104 to the first chamber 110 will be colder than that returning from the cabin heater 106 but it will mix with the warmer coolant from the cabin heater 106 before being returned to the engine 101 and so it will not have such a dramatic cooling effect on the temperature of the coolant passing through the engine 101 as would be the case if only cold coolant from the radiator were to flow directly to the engine 101 and the thermal shock to the engine 101 is therefore lower.

The cooling effect of the coolant entering the first chamber 110 from the radiator 104 will then act so as to cool the temperature responsive actuator 122 so that it remains controlled by a combination of the temperature of the coolant in the first and second chambers 110 and 110.

In practice the temperature of the coolant in the second chamber 111 is normally arranged to be dominant.

This combination of temperatures has the effect of damping any large fluctuations in movement of the valve member 121 and the valve member 121 and so produce only coolant temperature ripples and not large swings in coolant temperature.

A dual flow thermostat assembly according to the invention therefore provides an engine warm-up speed that is virtually as fast as that for an outlet controlled thermostat without the large temperature swings normally associated with an outlet controlled thermostat that increase thermal stress in the engine.

With reference to Figs 7 and 8 there is shown a second arrangement for thermally connecting the temperature responsive actuator 122 to the dividing waIl 115.

-12 -The thermostat assembly comprises of a first housing defining the first chamber 110 and a second housing 141 defining the second chamber 111.

The dividing wall 115 is formed as an integral part of the first housing 141 and has recess in which is press fitted the temperature responsive actuator 122 such that an end face 124 of the temperature responsive actuator 122 is abutting the dividing wall 115. The dividing wall 115 has a tubular portion 150 extending into the second chamber 111 in which an end portion of the temperature responsive actuator 122 is located.

The tubular portion 150 defines in combination with the end portion of the temperature responsive actuator 122 an annular chamber 151 in which the coolant is cooled by the dividing wall 115.

The temperature of the wax element (not shown) is therefore based upon the temperature of the dividing wall as transferred to the temperature responsive actuator 122 by its engagement with the dividing wall 115 and through transfer from the coolant located in the annular chamber 151 and the temperature of the coolant in contact with the portion of the temperature responsive actuator 122 not located within the annular chamber 151.

With reference to Fig.9 there is shown a third arrangement for thermally connecting the temperature responsive actuator 122 to the dividing wall 115.

The dividing wall 115 is formed as an integral part of the first housing 141 and has a tubular portion 150 extending into the second chamber 111 in which an end portion of the temperature responsive actuator 122 is fitted such that an end face 124 of the temperature responsive actuator 122 abuts against or is located adjacent to a part -13 -of the dividing wall 115 located within the tubular portion 150.

The temperature of the wax element (not shown) forming part of the temperature responsive actuator 122 is therefore based upon the temperature of the dividing wall 115 as transferred to the temperature responsive actuator 122 by its engagement with the tubular portion 150 arid the temperature of the coolant in contact with the portion of the temperature responsive actuator 122 not located within the tubular portion 150.

With reference to Fig.10 there is shown a fourth arrangement for thermally connecting the temperature responsive actuator 122 to the dividing wall 115.

As before, the thermostat assembly comprises of the first housing 140 defining the first chamber 110 and the second housing 141 defining the second chamber ill with an inlet 117.

The dividing wall 115 is formed as an integral part of the first housing 141 and has tubular portion 150 in which is fitted the temperature responsive actuator 122 such that an end face 124 of the temperature responsive actuator 122 is abutting the dividing wall 115.

A tubular member 160 has a bore press fitted onto the tubular portion 150 so as to attach it thereto. The tubular member 160 extends outwardly from the dividing wall 115 into the second chamber 11 and surrounds the temperature responsive actuator 122 for substantially it entire length so that it defines in combination with the temperature responsive actuator 122 an annular chamber 152.

In the example shown, the tubular member 160 is made from a thermally insulating material and has a number of -14 -apertures 161 spaced out along its length and around its circumference to permit coolant from the second chamber 111 to enter the annular chamber 152.

The temperature of the wax element (not shown) forming part of the temperature responsive actuator 122 is therefore based upon the temperature of the coolant located in the annular chamber 152 which is determined by the heat transfer or cooling effect of the dividing wall 115 on the coolant located in the annular chamber 152 and on the transfer of heat from the bulk of coolant in the second chamber 111 through the tubular portion 160 and on the temperature and flow rate of coolant from the bulk of coolant in the second chamber 111 through the apertures 161.

With reference to Fig.ll there is shown a fifth arrangement for thermally connecting the temperature responsive actuator 122 to an aluminium dividing wall 115.

As before, the thermostat assembly comprises of a first housing 140 defining the first chamber 110 and a second housing 141 defining the second chamber ill.

The dividing wall 215 is formed as a separate part and is secured to the housing 140 by any suitable means. The dividing wall 215 has recess in which is press fitted the temperature responsive actuator 122 such that an end face 124 of the temperature responsive actuator 122 is abutting or is adjacent to the dividing wall 115.

The temperature of the wax element (not shown) forming part of the temperature responsive actuator 122 is therefore based upon a combination of the temperature of the dividing wall 215 and the temperature of the coolant in contact with the portion of the temperature responsive actuator 122 not engaged with the recess in the dividing wall 215.

-15 -With reference to Fig.12 there is shown an alternative temperature controlled valve assembly in which a conventional proprietary wax thermostat assembly 220 is used.

The thermostat assembly comprises of a first housing defining the first chamber 110, a second housing 141 defining the second chamber 111, a thermally conductive dividing wall. 115 formed as part of the first housing 140 and an outlet tube 142 for connection to the top hose TH.

The wax thermostat assembly 220 comprises of a temperature responsive actuator in the form of a wax filled body 222, a valve member 221 fastened to the wax filled body is 222, a valve seat 225, a pushrod 223 and a spring 226 which biases the valve member 221 into contact with the valve seat 225.

Operation of the wax thermostat assembly 220 is conventional in nature, when the wax is heated it expands pushing out the pushrod 223 which causes the wax filled body 222 to move against the action of the spring 226 thereby moving the valve member 221 away from the valve seat 225.

In use coolant enters the second chamber through the inlet 117 and when the valve member 221 is in an open position exits via an outlet defined by the outlet tube 142.

In this case the thermal connection between the temperature responsive actuator formed by the wax filled body 222 and the dividing wall is formed merely by the close proximity of an end of the wax filled body 222 to the dividing wall 115.

Although the invention has been described with respect to several embodiments it will be appreciated that it is not limited to these, for example the dividing wall may have a -16 -number of fins thereon to improve the transfer of heat between the dividing wall and the coolant in one or both of the chambers.

It will also be appreciated that the first chamber could he formed as part of a housing for the circulation pump or one of the chambers could be formed as part of an engine block of the engine or a cylinder head of the engine.

It will also be appreciated that the dividing wall could be formed as part of the temperature controlled valve assembly which is sealingly fitted in a bore to define two chambers.

Although in the examples described the flow to the radiator is via the top hose and the return flow is via the bottom hose, it will be appreciated that the invention is not limited to this arrangement and that the flow to the radiator could be via the bottom hose and the return flow could be via the top hose.

The dividing wall in all cases is made from a material having a high thermal conductivity such as aluminium or copper or alloys thereof.

Although the temperature responsive actuator as described herein is of the wax filled type it will be appreciated that other forms of temperature responsive actuator could be used.

Therefore in summary the invention provides a dual

stream thermostat mounted at the engine outlet which can sense the coolant temperature at the inlet to the engine and the coolant from the outlet of the engine. This gives the benefits of an unpressurised radiator circuit with fast response so enabling optimum warm-up with minimum thermal stresses. The thermostat is characterised by a highly -17 -conductive heat transfer plate that is in contact with the inlet fluid stream. Initially the thermostat will be purely outlet controlled, but when opened, the low temperature of the inlet (or "bottom") hose coolant flow will influence the thermostat position through cooling of the wax element thermally attached to the heat transfer conduction plate.

This influence is what makes the thermostat "dual stream" and so enables a faster warm-up response than typically associated with an outlet thermostat but with smaller swings o in temperature due to the damping effect of the cool coolant returning from the radiator.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that one or more modifications to the disclosed embodiments or alternative embodiments could be constructed without departing from the scope of the invention.

Claims

-18 -Claims 1. A thermostat assembly for a cooling system of an engine

comprising a first chamber having an inlet and an outlet, a second chamber having an inlet and an outlet and a temperature controlled valve assembly having a valve member moveable by a temperature responsive actuator located in the second chamber to control the flow of coolant from the inlet to the outlet of the first chamber wherein the second chamber is separated from the first chamber by a thermally conductive dividing wall and the temperature responsive actuator is thermally connected to the dividing wall such that the opening an closing of the valve member is based upon a combination of the temperature of the coolant in the is first chamber and the temperature of the coolant in the second chamber.
2. A thermostat assembly as claimed in claim 1 wherein the inlet to the first chamber is connected to a return from a radiator forming part of the cooling system and the outlet is connected to a supply to the engine and the inlet to the second chamber is connected to a return from the engine and the outlet is connected to an inlet of the radiator.
3. A thermostat assembly as claimed in claim 2 wherein the supply to the engine is an inlet of a circulation pump used to circulate coolant through the cooling system.
4. A thermostat assembly as claimed in any of claims 1 to 3 wherein the temperature responsive actuator is thermally connected to the dividing wall by being located in close proximity thereto.
5. A thermostat assembly as claimed in any of claims 1 to 3 wherein the temperature responsive actuator is -19 -thermally connected the dividing wall by being attached to the dividing wall.
6. A thermostat assembly as claimed in claim 5 wherein the temperature responsive actuator has an end face in contact with the dividing wall.
7. A thermostat assembly as claimed in claim 5 or in claim 6 wherei.n the dividing wall includes a recess and an end portion of the temperature responsive actuator is fitted in the recess.
8. A thermostat assembly as claimed in any of claims 1 to 3 wherein the temperature responsive actuator is thermally connected to the dividing wall by having a least a portion located in coolant cooled by the dividing wall.
9. A thermostat assembly as claimed in any of claims 1 to 8 wherein the dividing wall has a tubular portion extending into the second chamber in which an end portion of the temperature responsive actuator is located.
10. A thermostat assembly as claimed in claim 9 when dependent upon any of claims 5 to 8 wherein the tubular portion defines in combination with the end portion of the temperature responsive actuator an annular chamber in which the coolant is cooled by the dividing wall.
11. A thermostat assembly as claimed in claim 1 or in claim 2 or in claim 9 wherein the assembly further comprises a tubular member attached to the tubular wall and the temperature responsive actuator is located within the tubular member so that an annular chamber is defined between the annular member and the temperature responsive actuator in which the temperature of the coolant is based upon a combination of the temperature of the coolant in the second chamber and the temperature of the dividing wall.

-20 -
12. A thermostat assembly as claimed in claim 11 in which the annular member has a number of apertures therein to permit the coolant in the second chamber to flow into the annular chamber.
13. An engine cooling system having a thermostat assembly according to any of claims 1 to 12.
14. A cooling system as claimed in claim 13 wherein the engine cooling system is a cooling system of a motor vehicle and the cooling system further comprises a cabin heater having an inlet connected to the cooling system at a position upstream from the temperature controlled valve assembly and an outlet connected to the first chamber.
15. A cooling system as claimed in claim 14 wherein the inlet to the cabin heater is connected to the second chamber.
16. A thermostat assembly substantially as described herein with reference to any one of figures 5 to 12 of the accompanying drawing.
17. An engine cooling system substantially as described herein with reference to Fig.5 of the accompanying drawing.