This post is for a friend of mine. He has a 94 PEP with stock sequential twins at 14psi, Power FC, ported wastegate, and a bunch of other supporting mods and crap. The important thing is that he has a Greddy FMIC and an upgraded radiator (had a Fluidyne, and then he had a custom one built that was even more efficient) with OEM 180 degree thermostat. The stock undertray is on and there is some semblance of custom ducting to direct flow to the radiator. When it's hot out (say over 85 F) the car runs hot... it gets up to about 210 F without even running the car hard. He also tried replacing the stock fans with a single large cooling fan that is coming on around 180 F.

It doesn't get hot enough to necessarily damage anything, but it's hotter than he should be comfortable with.

Now I'm an FC guy. I have a Greddy 3 row FMIC on my car with a Fluidyne radiator, and for a while it would occasionally run a little hot, but it turns out I had some stubborn air pockets in the system. But I also have the stock FC oil cooler which is absolutely enormous compared to the pathetic FD oil cooler on the non R1 models.

Could my friend's FD be running hot due to a stubborn air pocket? I remember reading that there is a tricky procedure to getting all the air bubbles out of the FD due to the AST (which my friend has replaced with an aluminum unit). I am about to order that air bubble elimination tool mentioned in the "big fat FD3S cooling thread"

Or should I tell my friend to go for one of those $1000 dual oil cooler kits?

 

At what temperature are the fans turning on? As I remember, the stock thermo switch doesn't even turn on until 205F. If the fans turn on earlier, does it still get up to 210?

My car gets hotter sitting at idle waiting for the fans to kick on then it does on the track sometimes. The biggest thing is getting air over the radiator. Freeway driving should give you the lowest numbers. Bumper to bumper around town driving should give you the worst.

 

My car runs the coolest at speed even when flogging. Air flow is king!

I would say the car gets the hottest during traffic or stopped. When not moving, have you tried turning the heat on and running the fans? This ramps the radiator fans to full speed (at least I think it does someone else can confirm). This always brings down my temps.

 

Turning on the AC on w/ 3-4 setting runs the fans on high.

 

Look if he has a power fc, he can turn the fans on at any temperature he wants.all other things being equal it works great.
before I put my powerfc on the car would run up to 100C on a hot day.After setting the fans on the commander to 86C,88C and 90C respectively my car seldom goes over 90C.

 

^^u need the datalogit to set the fans to a desired temperature. i have mine set at 90c for all three settings.

 

Air trapped in the cooling system could certainly be the culprit.
I think your friend has to perform the Air Bleeding procedure multiple times until the coolant stays at the full or neck level of the filler cap. Check coolant if it's still good, used soft water (demineralized) or distilled. Check the fan if it actually operates and no blades are broken (happened to me).
The stock thermostat should start opening at 177 F and be fully open at 203 F. The fan operation can also be manipulated by the PowerFC as pointed out by the other posters.

My car is bone stock and has always had the "cooling problem" since new (especially in the Florida summers and getting caught in traffic) but has since been corrected after installing a Koyo radiator.

 

In my experience with air in the system, it resulted in more of a temperature spiking issue than a steady temp increase where it then remained stable. Dual oil coolers help, and the FMIC probably has some influence in higher temps even with the upgraded radiator. But what ratio of coolant to water? How long has it been since he flushed the system? And have you checked all the fan speeds/relays? What settings is he using for the fans?

 

210f is not excessive. and the single fan is a bad move

 

He has converted to a large single fan that I presume flows more air than stock. It has its own shroud and ducting and is coming on at 180. The stock thermoswitch and all that junk has been bypassed, so that is not a concern. It seems like the temperature creeps up at stoplights sometimes but never really goes back down. It's especially bad if we drive the car around, park at a gas station for a few minutes, then start the car up again. It climbs to about 210 while heatsoaking in the parking lot and just stays there, or only drops to about 205.

I think he is just using premixed 50/50 from the auto parts store. I will send him the link to the coolant burping procedure first.

 

The FMIC setup itself is the culprit. It cannot flow enough air through it to satisfy the cooling demand, especially under warmer ambient conditions. This is not an unusual problem. And it's really not going to matter what the radiator is and what fans you are using. Some people have bypass air around the IC directly to the radiator, which helps, but the underhood temps are still going to be rather high.

 

Heat transfer is a function of the temperature difference between the coolant in the radiator and the air flowing across it. Obviously when it is warmer outside the delta temp is less. Add the FMIC which is essentially pre-heats the air flowing across the radiator and pretty soon you don't have enough delta temp to adequately remove heat from the coolant.