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1989 Sport Roof White Pkg 7M-GTE
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51 Posts
Discussion Starter · #1 ·
I am starting to get very frustrated.

Okay, with the hood open, the radiator fans cycle on and off just like they are supposed to.

With the hood closed, an external temperature probe reads 231 under the hood with the AC compressor off. With the compressor on the temperature goes to 234 and the needle goes to about 3/4 on the gauge.

Rubber gaskets at top and bottom of hood have been removed.

The car has an aftermarket 3” all aluminum radiator so there is no longer room for the factory mechanical fan so I am stuck with the mishimoto electric fans. I was told they must be working because they cycle on and off.

The problem at this point is that hot air is trapped under the hood and unable to escape. When the hood is closed it gets hot; when the hood is opened the temp IMMEDIATELY drops to normal. Four guys with over 100 years of combined experience say they’ve never seen anything like this.

Although it could be driven with the AC compressor off, he is not comfortable with me taking the car this close to overheating and given that summer is coming in Houston I am not excited about running without AC either.

We are completely at a loss as to what to do. Is there any kind of aftermarket device that will suck air out from under the hood?
 

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1987 Toyota Supra
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431 Posts
Are you driving around at very low speeds for a long time or normal road highway speeds?
Standstill ambient temps underhood are not unusual to be quite high with these engines.
Though I could leave mine idling for half a day and never overheat.
The area around the turbo is insanely hot, much higher than 240F
What does the coolant temp readout ? (Actual temp gauge not the OEM )
That's what really matters, if the air temp is high then the heat exchangers are doing their work.
What temp thermostat are you using?
What type of water pump is installed OEM? Or aftermarket?
Have you compared the OEM belt driven fan to the electric fans?
The OEM fan is going to move a lot more CFM.
 

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97 HARD TOP
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1,013 Posts
What does your actual coolant temp get to? engine bay temp and coolant temps are two very different things to worry about. If coolant is getting that high you may have some other (costly) engine problems to worry about. As far as engine temps go there are a fewer cheaper methods you could go. I simple aftermarket vented hood will let the air escape easier. You could make a simple air diffuser out of aluminum on the bottom of the car. I only have own mkivs, never a mk3 but i would assume they have factory plastic pieces that go on the bottom as well that should help it. I also don't know what your engine bay looks like(stock or upgraded) you could always heat wrap your headers and exhaust,turbo blanket, ECT. Now on the other hand if it's your coolant temp and you actually don't have a bhg, I would ditch the crappy mishimoto electrics and go with something a little stronger and more cfms. Also given where your at try running without a thermostat(i know people are going to disagree here) . but when I'm running mine in arkansas I always pulled mine and never had any issues with over heating even after doing constant pull after pull on the highway. Hope this somewhat helps
 

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I’m reading along @finaltable and nodding my head and then I’m reading @Piratetip and nodding my head. Multiple folks have called the mushymoto fans bad/terrible, I’ve seen that on a few places now. Try a mechanical fan, better electric fan. I had mentioned a lower thermostat or no thermostat also. The folks from the original thread even said the radiator probably wouldn’t help the initial problem.

OG forums peeps can’t you swap in like a 2j or 1j clutch fan to gain like a half inch or something?

ducting, ducting, if the belly pan is gone fab one or find one. Heat wrap and insulate everything

the removing the rubber around the hood I’ve never heard but sure why not. I’ve heard raising the rear of the hood too but idk if that even works

My opinion is the car was designed from the factory to go into thermonuclear meltdown if driven/stopped waiting in traffic on a hot day in the southeast with the AC running. The OEM sold it that way, yes.
 

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1987 Toyota Supra
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431 Posts
For reference I run an OEM radiator, fan/clutch and shroud.
All new components.
I also spent a lot of time sealing all the gaps around the perimeter of the radiator.
So all air being pulled by the fan has to move through the radiator.
It cant sneak around the side and pull stray air.

These engines are just hot, always have been.
It's normal.

Actual coolant temp is what matters as others have mentioned.
If you are overheating then your electric fans are likely not up to the task when at a standstill.
 

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1989 Sport Roof White Pkg 7M-GTE
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51 Posts
Discussion Starter · #6 ·
Some updates. They have burned an entire tank of gas testing this car, both in city driving and on the highway. (The shop is about 2 miles from a 70 mph highway so it is easy to test any scenario.)

The temperatures do this idle/city/highway.

The temp probe is testing the coolant itself which is reading 231. The water pump is OEM. The thermostat temp is 180. The trigger seems to be the AC compressor. With it off, temps are borderline but acceptable. With it on I was told the coolant temp got to 240.

One of the two main mechanics thinks that the Mishimoto fans are not moving enough air.

The bigger radiator helped but using the OEM mechanical fan is no longer an option because of clearance.
 

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Everyone else said it and I am going to say it again, but with extra emphasis:
The Mishimoto fans are garbage and will not provide proper cooling.

The methodology behind electric fans is a fairly complicated one and I've typed it out more than I care to admit, so you'll either have to research it yourself or just take some advise here. Just replace the junk fans you have now and replace them with some proper E-fans.

Your 2 best options are going to be the Spal 30102038 12" fan or the Maradyne TA12A3001 fan. I've personally used the Maradyne fan with the Mishimoto fan shroud and can confirm that they will fit with a little bit of work. Both fans will pull a fair bit more current than your current fans so you'll need to rewire them properly. Your wire length will ultimately dictate the wire gauge you need but figure 12ga wiring for each fan.
 

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1989 Sport Roof White Pkg 7M-GTE
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51 Posts
Discussion Starter · #9 ·
Everyone else said it and I am going to say it again, but with extra emphasis:
The Mishimoto fans are garbage and will not provide proper cooling.

The methodology behind electric fans is a fairly complicated one and I've typed it out more than I care to admit, so you'll either have to research it yourself or just take some advise here. Just replace the junk fans you have now and replace them with some proper E-fans.

Your 2 best options are going to be the Spal 30102038 12" fan or the Maradyne TA12A3001 fan. I've personally used the Maradyne fan with the Mishimoto fan shroud and can confirm that they will fit with a little bit of work. Both fans will pull a fair bit more current than your current fans so you'll need to rewire them properly. Your wire length will ultimately dictate the wire gauge you need but figure 12ga wiring for each fan.
Thanks for the advice. Two Maradyne fans ordered. They know how to do the wiring but appreciate the head's up.
 
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