Random Overheating?

[MRice]

To get this out of the way now its not a BHG compression tested/no coolant in cylinders. Its not the heater core because i have a brand new one installed by Toyota. The turbo has no leaks and the coolant system has no leaks either (compression tested) But still my car will overheat, it wont even do it at all at first but 5min into the drive it skyrockets for some random reason then as soon as i brake hardish or turn the car off for a second it goes right back to normal
and then i can push it rediculously hard and no change in heat and i mean ever i had my spool gauge maxed no change in heat or anything so what the hell is going on? it only seems to be doing this when it starts cold though... which leads me to believe a hose is tempidly plugged or something and thus it dosnt get coolant to a certain part fast enough? Any thoughts?????????? Temp gauge? Rad is 1 year old

[Bill UK]

Could be the temp sender unit.
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&Page=113

[Bill UK]

This should help

[Supra2NR]

I remember sumbody sayin that
If your temp gauge is acting like its possed it could be air in your coolant sytem
Try bleeding the coolant and see if this fixes the problem

[IHateHacks]

I would try changing the thermostat.

Or you could install an aftermarket water temp gauge, (to see if its a gauge problem which I doubt) by removing the stock gauge sensor (in that pic), and installing the aftermarket sensor in its place.

Have you tried block testing it yet? That's the ONLY way to tell if you have a blown head gasket or cracked head, block, cylinder. It checks for exhaust gas in the cooling system, no other test does this.

I hate to say this but my car did the same EXACT thing, random overheating, shut it off for 1 minute and start it and the temp comes plunging down to normal. It would overheat as soon as it warmed up from a cold start one day but the next day I would beat the crap outta it on the highway and it would not overheat, but then it would when I was just crusing the next day. Compression on my motor was 180 in all cyl's. Pressure tested my cooling system it checked out fine (held 15psi for 10 minutes). Never burned or used any coolant. You can check my post in MKIII section to see what my problem was.

[3RD STRIKE]

I had a simular prob. It was the radiater cap. they leak some times just enough to release the steam presure and not any coolant so ya cant find a leak. this prob was making my temp gauge redline. but the engine was not getting that hot. i changed the cap prob. fixed.

[ddmcse]

you say it's overheating

but does it actually piss water from somewhere or is it just that the temp Gauge goes crazy and jumps to the red zone ?


my gauge does that and thats why i have an aftermarket gauge

[scruffboy]

Have you tried getting any codes from the diagnostic box? That could give you a place to start looking. It may be a faulty coolant sensor, but you'll have to check. There are a lot of places to find the code "definitions", but I forgot the site's name that I used. Maybe someone else here can point him in that direction. I know you guys helped me with this.

Scruffboy

[dave in indy]

I had the same problem. Look for scale or mineral deposits on your radiator. I had a hair line crack on my radiator at the neck for the upper radiator hose. I would pop the hood and not see any coolant leaking. Then when I woke up I'd find a puddle of coolant under the car.

[MRice]

All great comments and things ive mostly looked into spring is back and my cars on the road but about 5mins into driving it still overheats and it appears steam is comming from my rad but looks as if might be the rad cap because the rad is new and was compression tested recently (Aka after it started overheating)

So I guess ill change the rad cap and if that dosnt work whatre your thoughts?

MRICE
Cheers