First time owning a legendary Supra really could use some help.
 

Hi everyone who reads this,

I hate to bother people but I really want to figure out this problem before it turns into something worse. Just bought a 1988 Toyota Supra non-turbo, rescued it from rotting.. it drives great but has just started to have some weird issue with the temp gauge.

It fluctuates rapidly, happens like this: I warm the car up in the warming, get it to it's normal below medium temp and take off for work.. about 10 minutes into the drive the needle will rocket up to the H for five or more seconds then shoot back down to middle or below mid... then right back up, repeating this process throughout the drive.

The oil isn't milky and is still clean.. no bubbles, the cap did have some steam coming from it when I parked it this afternoon, I let it idle and it stayed hot. I'm going to replace the thermostat tonight to see if it was just stuck.. but.. I'm having doubts there as well.

I'm really confused and could use some help,

Thanks.

Could be a faulty thermostat or maybe you're low on coolant? I had fluctuating temps and I later found out that I was leaking coolant. But yeah let us know once you check that thermostat

Sounds like air pocket(s) in the cooling system, probably been hiding in the heater core. Couple of ways to deal with it. Park the car on an embankment with the nose much higher than the tail, pop the radiator cap and let the engine run for a while to evacuate the air trapped in the system. And/or, loosen the bleed screw on the coolant line on the front/left (looking at the engine from the front) side of the engine to allow air to leak out of the system.

Once you get all the air evacuated your temps should stabilize and not dance all over the place.

I changed the thermostat last night and haven't had an overheating issue to or from work. :)

I'd also consider replacing the radiator cap. Cheap insurance.

How'd the coolant look? If it's been sitting there could be a fair amount of trash in the system, especially if the previous owner(s) didn't maintain it well.

So far so good.. been driving it around the phoenix area with no issues. I think it might actually be maintaining a cooler temp than when I first got it.

The coolent is clear of any debri and isn't murky by any means. Just needs a good tune up and some seals replaced now.

I'll keep my fingers crossed for you.

standard cheap troubleshooting when dealing with temp issues is to replace the thermostat and the rad cap and burp the system. as stated above the fluctuating temp could be a result trapped air pockets.

In the summer time I always use a low temp fail safe thermostat. between 140 or 150 degrees. When and if it fails it just sticks in the opened position so no harm will be had to your engine. Costs a little more but were talking maybe 5 additional dollars.

Yes I know (to low thermostat) can cause issues also, by not running at recommended temp. I disregard this information because I'm a loose cannon and a lightweight masochist.

...says the MKIII Supra owner. :rofl2:

Middle weight at the very least.