Mainly because when you turn off the engine, the fan stops, so all the heat kinda builds. Hence the reason for Turbo Timers, it allows the engine to cool itself down for a couple minutes after you turn the car off.

 

Yup, anyone with an aftermarket temp gauge will see the car gets pretty f-n hot after you shut it off. There's nothing you can do about it short of installing an electric fan. All the MK3's do it. The trick is the engine itself doesn't produce anymore heat, it's just that the hot water naturally moves up where the temp sensors are so it appears the car is getting hotter.

However you should have pressure in your hoses, if you don't then you have a problem somewhere. The Supra is a closed pressurized system and once it warms up it should have roughly 12psi of pressure throughout the system.

I wouldn't worry about the temps though, +115C is where the damage starts happening. Mine runs roughly 90-95C without AC and almost 110C with the AC on in the heat of the day and heavy traffic.

 

You should deffinately have pressure in the system. Either your radiator cap is not sealing properly, or you have a small leak somewhere.

As far as the car heating up after shut down, every single engine does it. This is when the highest temperatures occur, but since it happens so slowly and nothing is moving, it doesn't really put any stress on the engine.

It's nothing to worry about, and is not bad in itself.

 

You should deffinately have pressure in the system. Either your radiator cap is not sealing properly, or you have a small leak somewhere.

I doublechecked EVERY connection, hose and everything everywhere.. I cannot find a leak.. coolant stays the same level.. NEVER goes down or drains.. so obviously there isnt a leak.. but
any other ideas about pressure? how can i solve this ??

 

I doublechecked EVERY connection, hose and everything everywhere.. I cannot find a leak.. coolant stays the same level.. NEVER goes down or drains.. so obviously there isnt a leak.. but
any other ideas about pressure? how can i solve this ??

Can you still squeeze the hose after shutting down a hot engine? It should be very firm to the touch.

I would look more closely at the radiator cap. Inspect the rubber seals and valves/springs, and if you have another unit handy put that in to see what happens.

Do you still have the stock Toyota radiator? If so, I remember reading on Reg Reimers site, how there are different radiator caps for different years of stock radiators, and are not interchangeable.

 

yes i have stock radiator and i bought a new radiator cap from toyota... tell me how?

 

yes i have stock radiator and i bought a new radiator cap from toyota... tell me how?

http://www.supras.com/pub/SONIC/MA70/RADCAPS.txt

There are 3 styles of rad caps used on Supras, all three are unique in design and can not be mixed and matched. One of the designs is better than the others. You will have to use the correct cap for your type of radiator. I recently ran into a 1987 Supra Turbo with a rad from a 1990 or newer. The owner was trying to use the cap from the 87 and was driving the car with no pressure in the radiator.

Style 1. Pn# 16401-36011 Rad Cap is the large round one used on all years MA-67's, it is also used on most older Toyota cars, trucks & fork lifts. This one is the best of all the types and will last much longer than the other two styles. They are used on all opper
radiators only.

Style 2. Pn# 16401-83010 Rad Cap is a small diameter cap used on 86.5 to 90 MA-70's, it has very small seal areas and is prone to early failure. My 1990 V6 4 runner is now on its 3rd one in 20,000 miles. I replace them every 24 months or 50,000 miles. If you have a 87 to 90 Supra and don't know if you have changed your rad cap, you need one, go and buy one today!

Style 3. Pn# 16401-72090 Rad Cap is also a small diameter cap it is used on 1990 to 1996 Toyota Supras. This cap looks very much like style 2 but has redesigned seals, this style will last longer than style 2 but not as long as style 1. I would recommend changing it at the same intervals as the style 2 cap just to be safe.