Engine over-cooling
Discussion
Dave, thanks for your early morning comment, fully agree, this was my understanding so far as well. But still asking myself: When the thermostat is fully open at a certain temperature, lets say 88°C ,it allows full waterflow through the rad. It then leaves things fully to the cooling system to keep the 88°, avoiding overheat in traffic by support of fans.The cooling system and its capacity was designed to work under certain conditions including outside temperature so ist fully up to the Job even in hot summer. But if the ambient temperature is a lot lower like in winter, the capacity of the cooling system is too large so the water temperature may drop significantly below the 88°. But shouldn't the thermostat come into play then by gradually closing and therefore reducing waterflow through the rad to allow a "comfy" temperature of the water circulating in the engine? As you say the stat doesn't snap open, it would also not snap shut I guess. It just strikes me that you would have to limit the airflow through the rad by whatever material to avoid overcooling instead of leaving that job to the stat? Or maybe I'm thinking the wrong way.
FoxTVR430 said:
Taylormj4
Maybe it's a case of your thermostat sticking open, or not being there at all!
As others have said, the thermostat is there to help get your engine up to temp ASAP.
But suppose it is always open. Then the car would generally take longer to warm up.
As you drive along on these cold winter days the cold air flow through the radiator will cool the engine water temp down as the thermostaat will not shut the flow of water to the radiator. Thus making the whole water system cooler.
As you said your temp gauge is working and showing the drop in water temp, the air feels cooler from the heater, etc..
But when in traffic the engine water temp would rise to the temp that the otter switch would turn on the fans. The fans would draw cool air through the radiator cooling the water until the otter switch turned them off. The thermostat will always be open in these conditions.
Indeed. A temporary fix for poor cooling on an engine used to be to remove your thermostat so that it ran at lower temperatures and gave you a bigger buffer for when you got stopped in traffic. However, on some cars, the thermostat forms a seal between the pipes so if you remove it, the coolant leaks out, as I found on an old Rover in my youth! I plan to check the stat condition asap.Maybe it's a case of your thermostat sticking open, or not being there at all!
As others have said, the thermostat is there to help get your engine up to temp ASAP.
But suppose it is always open. Then the car would generally take longer to warm up.
As you drive along on these cold winter days the cold air flow through the radiator will cool the engine water temp down as the thermostaat will not shut the flow of water to the radiator. Thus making the whole water system cooler.
As you said your temp gauge is working and showing the drop in water temp, the air feels cooler from the heater, etc..
But when in traffic the engine water temp would rise to the temp that the otter switch would turn on the fans. The fans would draw cool air through the radiator cooling the water until the otter switch turned them off. The thermostat will always be open in these conditions.
The temperature rating on a thermostat is always when it will START opening and as you say it should be opening or closing as the temperature changes up or down. If its working properly then there should never be a large variation on gauge reading as just like a central heating thermostat it should maintain stable readings. Blocking off rad cores should never be necessary if its working properly because in theory if its that cold the thermostat will not allow much flow to the radiator. I never understand why anyone thinks you need a winter and a summer thermostat as its either working properly or not.
cureton said:
Dave, thanks for your early morning comment, fully agree, this was my understanding so far as well. But still asking myself: When the thermostat is fully open at a certain temperature, lets say 88°C ,it allows full waterflow through the rad. It then leaves things fully to the cooling system to keep the 88°, avoiding overheat in traffic by support of fans.The cooling system and its capacity was designed to work under certain conditions including outside temperature so ist fully up to the Job even in hot summer. But if the ambient temperature is a lot lower like in winter, the capacity of the cooling system is too large so the water temperature may drop significantly below the 88°. But shouldn't the thermostat come into play then by gradually closing and therefore reducing waterflow through the rad to allow a "comfy" temperature of the water circulating in the engine? As you say the stat doesn't snap open, it would also not snap shut I guess. It just strikes me that you would have to limit the airflow through the rad by whatever material to avoid overcooling instead of leaving that job to the stat? Or maybe I'm thinking the wrong way.
That is my understanding. The thermostat used to have a little wax cylinder in it that responded to the water temperature flowing past it by applying force against the spring. It is an analogue system and does not snap open or shut. Similar thermostats exist in mixer showers. When the stat starts to open, it will get a big blast of cold water that has been sitting in the radiator, which will cause it to close again, then when the engine heats up that water, it will start to open again. Gradually the temperature in the radiator and engine will stabilise and there won't be the big shock changes in temperature of water coming in from the radiator (expcept when the fans cut in) and the stat will find a position that matches that.The thing that the stat can't control is the cooling effect of the air rushing under the engine and up through the engine bay due to the forward movement of the car. That cools the block of the engine itself. If that effect is significant enough, and the engine is only at small throttle opening (cruising) it is possible that even a completely shut thermostat could not stop the temperature of the engine coolant from dropping. This was part of my question.
taylormj4 said:
When the stat starts to open, it will get a big blast of cold water that has been sitting in the radiator, which will cause it to close again, then when the engine heats up that water, it will start to open again. Gradually the temperature in the radiator and engine will stabilise and there won't be the big shock changes in temperature of water coming in from the radiator (expcept when the fans cut in) and the stat will find a position that matches that.
This all depends on which direction and location the pump and stat are in relation to each other. On most engines, the pump circulates the cold water on initial start and it stays within the block and heater pipes because the stat is shut. Once it warms up the stat starts to open so allowing the hot water to travel away from the engine towards the radiator. I cannot see how there is a big blast of cold water as the flow is the other way. There is pressure behind the stat caused by the pump so the flow can only go away from the engine to the rad. If you hold the top hose it warms up gradually along its length towards the radiator.If there is a fault in your car, I would say it is either the stat stuck partly open - hot or cold - or there is an air lock.
This may have the purist 'power seekers' running for the hills !
But who remembers air filters that used to have summer and winter settings ?
You would need to rotate the cover so that the inlet picked up air from near the exhaust manifold (very near if I remember correctly.
Some more sophisticated filters had a diverter valve in the inlet tube to collect air from near the manifold without moving the filter housing. (must have been motorised somehow).
Now here is a thought!
Has any body modified (truncated) the inlet duct to have the filter in the engine bay ? (as you did with carburetors)
Would it make much difference to temperature ? (they obviously used to think so)
I know we now have sophisticated ECUs (or 14CUXs) to control things better now and you loose power with the less dense air etc etc, but the advantages would be :-
Quicker warm up ?
Better throttle response ?
Less likely for filter to suck up water in floods - certainly.
Filter would keep cleaner - certainly.
Would it over heat in summer when stationary ?
Would the power drop be significant ? ( we all seem to agree once on the move the air under the bonnet cools anyway)
I know car makers (even or especially TVR) dont add cost for no reason, and lots of people have gone to great lengths to insulate the air duct, but, just thinking out loud you know.
But who remembers air filters that used to have summer and winter settings ?
You would need to rotate the cover so that the inlet picked up air from near the exhaust manifold (very near if I remember correctly.
Some more sophisticated filters had a diverter valve in the inlet tube to collect air from near the manifold without moving the filter housing. (must have been motorised somehow).
Now here is a thought!
Has any body modified (truncated) the inlet duct to have the filter in the engine bay ? (as you did with carburetors)
Would it make much difference to temperature ? (they obviously used to think so)
I know we now have sophisticated ECUs (or 14CUXs) to control things better now and you loose power with the less dense air etc etc, but the advantages would be :-
Quicker warm up ?
Better throttle response ?
Less likely for filter to suck up water in floods - certainly.
Filter would keep cleaner - certainly.
Would it over heat in summer when stationary ?
Would the power drop be significant ? ( we all seem to agree once on the move the air under the bonnet cools anyway)
I know car makers (even or especially TVR) dont add cost for no reason, and lots of people have gone to great lengths to insulate the air duct, but, just thinking out loud you know.
If you remember, the hot air selection for winter on carb engines was to prevent icing up of the venturi. (This happened on my RS2000 on the A66 in the middle of winter after I fitted pancake filters. 
)
Many modern air flow meters have built in air temp sensors (or separate ones) to help the ECU accurately deliver the correct mixture so moving the air filter inside the engine bay is not a good idea. As you say, colder denser air is necessary to get the maximum oxygen.
On initial start from cold the coolant temp sensor plays the biggest part (a modern version of a carb's choke) assisted by the airflow sensor/air temp sensor.
)Many modern air flow meters have built in air temp sensors (or separate ones) to help the ECU accurately deliver the correct mixture so moving the air filter inside the engine bay is not a good idea. As you say, colder denser air is necessary to get the maximum oxygen.
On initial start from cold the coolant temp sensor plays the biggest part (a modern version of a carb's choke) assisted by the airflow sensor/air temp sensor.
Edited by N7GTX on Friday 2nd December 09:13
N7GTX said:
If you remember, the hot air selection for winter on carb engines was to prevent icing up of the venturi. (This happened on my RS2000 on the A66 in the middle of winter after I fitted pancake filters. )
Many modern air flow meters have built in air temp sensors (or separate ones) to help the ECU accurately deliver the correct mixture so moving the air filter inside the engine bay is not a good idea. As you say, colder denser air is necessary to get the maximum oxygen.
On initial start from cold the coolant temp sensor plays the biggest part (a modern version of a carb's choke) assisted by the airflow sensor/air temp sensor.
All true of course!)Many modern air flow meters have built in air temp sensors (or separate ones) to help the ECU accurately deliver the correct mixture so moving the air filter inside the engine bay is not a good idea. As you say, colder denser air is necessary to get the maximum oxygen.
On initial start from cold the coolant temp sensor plays the biggest part (a modern version of a carb's choke) assisted by the airflow sensor/air temp sensor.
Edited by N7GTX on Friday 2nd December 09:13
Did wedges have filters in the engine bay, as they have injection etc ?
There is a preheat circuit that applies hot water to the underside of the plenum at the same time as the heater on the Range Rover set ups, but TVR blocked off the pipework on the basis that warm air is less dense and will therefore produce less power. Also you wont find my TVRs being used in arctic conditions where you might find a Range Rover. Just a small point of note on the thermostats- they come in two flavours- some have a small "jiggle" valve in the rim of the stat that allows any trapped air / steam pockets past the stat before it opens. The TVR should not need this type as the circulation of the heater water is not shut off when the heater is shut off- ie the heater valve is a bypass type of valve- not simply open / closed. This prevents steam pockets as you always have water flow around the head / block. If one is fitted by mistake it will slow the engine warm up, and the top hose will have heat before the stat opens, but its not a huge effect.
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