like the topic says, do stock FD's have a built in timed fan that continues to cool the engine down after the car is shut down? i'm looking at buying an rx7 and i asked if he takes proper time to let the engine cool down. he says he does, but also mentioned that even after he takes the key out, the car has an electric fan that continues to run for a few minutes. i saw it in person and it does indeed sound like a fan is still running after he turned the car off. i just wanted to know if this is a stock feature or if it's something that was added to mimic a turbo timer? thanks in advance.

 

Its a stock feature. I think they started this in 94. My FD does this sometimes. The fans will continue to run for a few minutes depending how hot the engine is when its turned off and will turn off when the water in the radiator reaches a certain temperature. This just cools the water in the radiator since the engine is off and the water pump isnt circulating water.

 

I have 93 fd and when i take the key out after a long drive my fans don't come after i remove the key but if i leave the key still in the ignition with the engine off, it runs.

 

Yeah. It does it when the engine temps are to high when the car is shut off. I did the fan mod to keep the temps down while driving and have not had the fans cut on after the car is shut off since then.

 

I tried to fix mine, got new relays and everything, but mine ran non stop all the time killing the battery. So what I ended up having to do is run a wire from the diagnostics box to the fan test, to a switch in the cabin, so I manually turn my fans on and off. Not super convienent, but it's not bad.

 

as i have^^ just dont forget to turn it on.

 

does the fan do a sufficient job of properly cooling down the engine? should i be worried that he seems to rely on the fan to continue cooling down the car after shutting down? he still lets the car run for about a minute before removing they, and then the fans kick in.

 

the fans are normal and a turbo timer is totally different.


When your car is running the turbo is cooled two ways, by the oil pumped through the bearing and (if fitted and additionally) a separate water line connected through the engines cooling system. BUT when you turn off the car, both these systems stop! Sure the fans may run, but this only cools the water in the radiator, not the engine, not the turbo!

The main aim is to never stop the car when the turbo is hot, as this causes the centre bearing to over heat (due to no oil flow) and eventually either seize or wear out very quickly.

From the start.
When your car is on boost, thermodynamically the turbine side (exhaust) gets extremely hot from the expanding gasses exiting the engine. This causes the centre bearing assembly to also get hot. This bearing is lubricated by engine oil, it is happy at temperatures up to 950 degrees centigrade! A temperature that is only achieved with antilag functions on race and rally cars.

On your car the turbo will glow red or orange (if you drive it hard) around 350 - 500 degrees, when it has been on boost for times from 2 minutes and upwards.
What the timer does is replace you, from waiting for the car to cool down when you are rushing to leave the car parked after you have driven quickly to a meeting or as such!
When it is in "on" position and you turn off the ignition and remove the keys, it counts down from the pre set time you have chosen, (allowing the turbo to cool) and the engine oil to pass through the bearing as well as the water around it (in a separate water jacket) keeping the bearing at a happy temperature.


from a quick search

 

There are people who keep the car running for several minutes after stopping but this is pure silliness - the engine will actually get hotter in this situation.

A don't take this the wrong way, but if you are worried about things like this I would buy any car other than an RX-7.

 

First, no need for a turbo timer to cool down, just drive the car under no boost for the last 5 minutes you're going to drive. If that means you're going to be late ... So Be It. "oh sorry, I was driving the FD." maybe next time leave early... why should your FD be sacrificed because you don't have good time management skillz

 

I'm confused here. Sure, if the car is idling, the engine (and engine coolant temps) will rise because of less air flow over the radiator. I'm guessing that even with the cooling fan on high the engine temp would still tend to rise. Keep in mind I'm ignorant and have only had my FD for a week, but the highest temps I've seen were when I was stuck in traffic in KC.

However, and please correct me if I'm wrong, the turbo temperature would be somewhat independent of engine temperature. If the turbos are really hot shouldn't the oil circulating through them cool them down even in an engine that is running hot at idle? So whille the engine temps may rise, wouldn't the turbo temps drop?

Just trying to learn here...

 

^^ That's the idea of using a turbo timer to cool the turbos, not the engine. You may want to look into the fan mod to cool the engine quicker. Couple of other local FD owners have done it and as soon as the fan shuts off the engine is cool enough to start working on... I was amazed. And supposedly it's pretty simple to do. If you're interested you can search or as a3dcadman (Chuck) or BlueShift (Chris)

 

Stock FD turbos are water cooled - hence it would be counterproductive to keep the engine running because the water would be getting hotter without decent airflow to the radiator.

Keeping out of boost for the last few minutes of a drive is the best way to ensure that you do not have superheated turbos when you stop.

 

In my reading through the stickies and archived threads it seems there are three different routes for changing how the electric fan operates.

1) One mod causes the fan to go to medium speed instead of low speed and high speed instead of medium speed. Not sure if makes the fan run continually at low speed when the engine is running. This sounds good other than in winter driving would it take longer for the engine to reach normal operating temp? As a not-quite-daily-driver I want the car to reach normal temps reasonably quickly.

2) A fan mod that essentially puts a fan switch in the car so the driver can turn the fan on and off at will. This would be very effective I assume but I don't think I'd want another switch inside my car and it is one more thing to forget to do. (not senile yet, but...)

3) A thermoswitch swap. Apparently a thermoswitch from an FC turns on at a lower temp than the stock FD switch. I think the stock comes on a 115C and the FC thermoswithc at 85-95C? Of the three, I like this the best as it seems easy and effective and doesn't require rewireing anything.

Is my understanding of these three basically correct?

 

Thanks for the clarification. I agree that driving easy for a few minutes sounds like the best solution I'm just trying to figure out how these things work.

How hot do the turbos get? Does it get hot enough to cause the coolant to vaporize? If the engine is at 240F and if the turbos are at say 500F, would a turbo timer cause some equalization of the temps? I'm guessing that the engine would have more thermal mass than the turbos.