In conventional cars, the water pump shuts off as soon as the engine stops; thereby the engine experiences the highest temperature after it is shutoff.
Is this the same with hybrid cars ? Or is the battery used to circulate the coolant after shutoff ?
Some, I believe.
Ford (and I think Toyota) hybrids have electric water pumps.
FWIW, my understanding from 30+ years of listening to Car Talk is that due to being electrical and thermostat-controlled, the cooling fan can continue to run after the car is shut off, even if the water pump does not.
Not exactly.
The heat source ends as soon as the engine is off. One millisecond later the engine & cooling system as a whole is cooler than it was a moment ago. And the entire system continues to cool monotonically until the whole thing is at ambient temperature a couple / few hours later. So this “… the engine experiences the highest temperature after it is shutoff.” is strictly speaking false.
What does happen is that while the total heat quantity continuously decreases it also redistributes. So some parts that were relatively very hot become cooler while some nearby parts that were relatively cooler become hotter. So there will be some components that experience their highest temperature minutes ro hours after the engine is shut off. But not the whole thing.
All this is a side issue to your Q about hybrids. But it bespeaks a fundamental misunderstanding of what’s going on.
Also, there’s no reason a non-hybrid pure ICE car can’t also have an electric water pump in addition to the now-common electric radiator fan. I don’t know enough about current car design to say whether any current non-hybrid cars do. But it’s certainly within the realm of engineering possibility.
yes. I believe some German makes do this now, as well as GM’s new 2.7 liter turbo truck engine.
@jz78817 I could also see a short-duration post-shutdown electric oil pump being useful to prevent turbo coking. And other oil badness in the highest temp areas of the engine proper.
In most gas engine vehicles, the water pump is a mechanical belt driven component that stops when the engine is shut off. There are some gas engine vehicles that use an electric pump also. Hybrid vehicles, generally speaking, have 2 cooling systems. One for the engine and one for the high voltage system. Sometimes there are 2 electric pumps, sometimes there is a mechanical pump for the combustion engine and an electric pump for the high voltage system.
Any electric pump certainly has the ability to keep pumping after the ignition has been shut off. It would depend how the manufacturer programmed the vehicle. I’ve seen warnings on Audi’s that the pump can operate at any time, similar to a cooling system fan warning.
I know that regardless of whether the vehicle is in ‘ready’ mode or the engine is shut off, if the ignition is on, the high voltage system pump is operating on every vehicle that I’ve observed. I’ve never had to test whether or not it operates when the ignition is shut off.
“ The phenomenon known as “heat soak” occurs when the engine is turned off. At this time, the combustion process is terminated. This terminates the momentum of the crankshaft, which in turn stops the turning of the water pump. As the coolant is no longer being circulated, the engine block and cylinder temperature increase for a period of approximately 3 to 10 minutes, depending on the engine design and additional components.”
(Bolding mine)
Exactly. Some parts of the engine is getting hotter while at the same time the whole thing is getting cooler. That is the “redistribution” I was talking about.
Which parts & locations within those parts tend to get hotter post-shutdown? The ones closest to the cooling system. Those which had been having heat actively removed from them before but now only have heat being passively moved out to the world & simultaneously moved in from other nearby even hotter parts.
Perhaps you’ve conflated “engine block” or “cylinder” for “entire engine & cooling system as a whole”.
I get it, LSLGuy, thanks. The Engine block and cylinders are at higher temperature than other parts, I believe. Anyways, I should have been more specific.
Thanks for all the answers.
I’m not sure it’s universal, but the majority of cars I’ve seen use turbochargers with water-cooled center sections.
The gen 2 Prius (not sure abut gen 3) stores warm coolant in a thermos at shutdown an uses it for starting. Gen 4 uses heat from the exhaust.
Brian
My 2002 VW had an auxiliary electric water pump that would run after the engine was shut off to help it cool down more evenly. I think it could run for up to 10 minutes, and you could see the water flowing through the coolant reservoir. They’re also used to provide more water flow to the heater core in many cars.
The whole purpose of the thermostat IIRC was to shut off flow to the radiator if the engine was not hot enough. The engine should be at a stable temperature when operating for clean and efficient performance. (proper combustion) In winter conditions, often the engine will not need to flow the full volume of fluid through the radiator to keep the engine at operating temperature.
The issue as discussed is simple - the contents of the cylinders burn. Consequently, the walls of the cylinder, and the whole piston, the valves, may be significantly hotter than the rest of the engine block. Turn off the engine and this extra heat redistributes by conduction to the engine block, and due to lack of movement, there is not much air flow cooling unless the water pump and fan/radiator are still in use (by electric pump and fan). So without any extra cooling, the rest of the engine block will absorb more heat from the cylinder and piston they surround to equalize temperature and bleed it off to the ambient air.
I am not a car guy, but I can buy an after-market electric water pump for some common conventional engines that don’t come that way.
Because at high speed the radiator is efficient, and you don’t have to keep making the pump go faster and faster (and using engine power) just because the engine is going faster. For guys who care about getting maximum power out of their engine, this is a thing.