So confused...cooling is fine when driving. Turn off car = overheat.
 

I have no idea what is causing this...but whenever I'm done driving and pull into park. Leave for about 5 minutes, then come back and try to start...my temp gauge goes through the roof! And then it's hard to start it because the engine is so hot...but the only way to cool it is to get the cold water from the radiator circulated. So it takes a few seconds of starting to get it circulated then it's fine?

What the heck could be causing this? I don't understand...I have aftermarket AST, KOYO radiator, all the cooling mods done, aftermarket water temp gauge...bla bla.

Any ideas? It makes it impossible to drive the car unless I let it sit. :(

Also, just wanted to add that the car starts up fine when cool and when at a normal operating temp, did the champagne bubble test and that came up negative, and it's not leaking coolant anywhere. Gaaar!

That's normal, its called heatsoak. It should still be able to start though and you just hold the revs a bit until the temps come down. If its hard to start, could be a few things. Fouled spark plugs, cold heat range spark plugs, or bad tuning.

thewird

Heatsok so bad it jumps up to 116-120 degrees? I mean...it doesn't feel normal to me. I don't remember it ever doing that before I had the rebuild.

Will it damage the car by doing that? It seems to run fine once the temps come down which only takes a few second. I can watch the temp on the gauge drop immediately once the coolant starts circulating. Maybe I should install a cryo cooler for the radiator and then blast it a few seconds before I shut down to help chill the temps? It's just annoying...

I'm having it checked out by a knowledgeable RX7 guru this weekend at Munkywurks Garage this weekend...so hopefully they'll be able to get it tuned up and running right. The entire thing needs a lookover by someone who knows a bit more than I do. I'm still learning engine management.

Well, I've never seen it that high but then again I don't live in Hawaii. I've seen 100-110C depending on the timing of the restart. A vented hood might help lol.

thewird

Thats pretty standard. You've got a giant cluster of scorching cast iron on your passenger side that loves to heatsoak the entire engine bay.

Have you thought about hooking up a Fan Controller? Just hook it up to battery source so it will turn on after you turn the key off.

I have a Power FC set to run the fans at a lower temp than normal, but no fan controller. It's not really the radiator that's the problem, it's the heatsoak that occurs to the engine itself.

Maybe we'll figure it out this weekend...I'll update if possible.

If your blowing air into your engine bay 5 minutes after shutoff, the heatsoak won't be as bad.

thewird

Could be low compression too, I'm sure you don't want to hear that ;)

I've seen my temps get as high as 115ish. Don't forget when you shut the car off the coolant stops circulating and the pressure climbs sky high.

I pop my hood after I park it in the garage and turn it off. Its not as nice as a vented hood, but it helps some of the heat escape.

115C is about as high as I have seen temps on a Hot restart on the PFC... they typically drop quickly though into the 90's in the first 2-3 mins of the engin running though

i've been seeing my car heat soak lately - hell it's summer.

while driving up to albany the other weekend, i stopped at a rest stop to take a piss and when i came back out and started the car it was up to 118. of course, within 30 seconds it was back below 90...and back to 85 by the time i was on the road.

that's why they had the recall to install an external module which makes the fans run when the engine is off. Although like everything else in the factory cooling system, it only comes on when it gets really hot.

https://www.rx7club.com/attachment.p...1&d=1248406842

Here is the Rx-8 system. Their stock ECU is mounted in the engine bay and the ECU has its own engine bay temperature sensor.

https://www.rx7club.com/attachment.p...1&d=1248406842

https://www.rx7club.com/attachment.p...1&d=1248407119

What's really interesting here is that Mazda seems to be really concerned about keeping water temps under about 108 C. On the Rx-8 cooling system, the fans come on at 97 C, two degrees higher than the temperature at which the thermostat opens completely (95 C). The FD first turns the fans on at 105 C. Both the FD and the Rx-8 crank up the fan speeds at 108 C, but the Rx-8 gives the cooling fans a greater operating range of temperatures at low speed. Also, I've looked through multiple service manuals and it appears that from the Rx-8's all the way back to the 1st gen Rx-7's, the factory thermostat has always cracked at 82 C and opened fully at 95 C.

THis is really interesting that Mazda was concerned with heatsoak on the RX8. My car 10 minutes after a hot shut down can go as high as 127C or roughly 260F. I run Evans NPG+ for the last 5 years with an auxiliary electric water pump to ensure that there is no hot spots despite the hotsoak at this temp.

See this: https://www.rx7club.com/showthread.p...light=electric

I've 29K on this Malloy Motor with Evans NPG+ from day one and it hasn't suffered any ill effect from the hotsoak at this temperature 124-127C routinely. Last year Steve K tuned it and made a dozen passes without any issues. I still see 13psi at least twice a day (once to work and on the way home).

This would be one of the few times I would recommend a vented hood for a street car, it would help in this situation.

Do the fans turn on if you turn on the AC with the engine off?

This has happened to me before. Once it starts it will circulate the coolant, all will be ok and the temps should immediately drop.

Regardless the car should start even at 116Deg. I don't know how the power FC works but I would work on my "cranking" fuel map. Likely the setting in the 116Deg range needs to be adjusted. On the Microtech you adjust this % fuel value until the car starts normally...and you do it at all temps from -24 to 124. Your car is likely adjusted for the normal temps of 85-100deg but the settings need to change as the car gets hotter.

Chris

I'm not sure...I'll check this. My A/C needs to be re-filled...but I'm concentrating on getting the car running right before I mess with a silly thing such as the A/C. :D

cranking fuel map maxes at 80 C

https://www.rx7club.com/attachment.p...1&d=1248454988

One more question: do you have your hot start (pressure regulator control) assist solenoid and fuel temperature sensor still installed?

https://www.rx7club.com/attachment.p...1&d=1248455928

I mentioned that because turning on the AC makes the fans run. If you notice your car is hot before starting it, maybe running the fans will help move the air inside the engine bay a bit. I know I would hate to start my car if its above 110.

+1 on the vented hood. When I was running one the temperature measured, on average, 30F degrees LESS at the intake at any speed, ditto underhood, and temps immediately started to drop after shutoff.

Fan mod + no boost 2 miles before home.

This might help things cool off a little in the engine bay so it doesn't get so hot...

my temps right after the 10 mins on the water temp gauge (sensor in the t-stat housing) goes down from ~180F to ~140F

Yea I always stop boosting when I get close to home. Thats pretty important.

Heat soak is normal, but a 120c heatsoak is not. Not even in Hawaii. Something is up for sure.

I always pop my hood whenever im done with my drive.

If for any other reason i dont want my hood open, ill run the fans for about 3 minutes or at least until temps go to about 180-185. Then ill shut the fans off.

VENTED HOOD...... PERIOD..... having an fd and no vented hood is just crazy especially if you drive it during summer time. I had a friends fd do the exact thing and a vented hood did wonders.