90 Supra comp temp gauge broken and overheating

Recently purchased a 1990 Supra comp with pcm 351 ford. Recently changed oil and impeller. Old impeller was missing rubber so I took apart thermostat housing to check for pieces. I found nothing. Mechanic friend said chunks probably blew through exhaust and not to worry so we took it out.

Temp gauge alarm goes off as soon as key is turned and gauge is either bottomed our pegged out or jumping all over. If I put finger pressure on it it shuts up.

Ran it about 15 min at idle and was cool to the touch. Drove about 15 min at mid throttle and felt warm but nothing alarming. Parked and fished and drove 25 min when we stopped it was boiling water in the engine. Stopped for 2 hours. I checked the thermostat and I had put it in with the spring facing up away from the engine. Made a phone call, the orientation seemed incorrect so I flipped it over. Restarted boat after cooling and immediately upon applying throttle felt water flowing in exhaust elbows. Boat ran another 20 minutes at 3/4 throttle and felt lukewarm to the touch but if I give it throttle would be cool. Noticed that after stopping it would heat up with engine off and as soon as I’d start it it would cool and as soon as I hit the throttle it would cool a lot more. Took it in. Parked it.

Where is the temp sending unit located? I need a working heat gauge! Where could I order new gauge and sender?

How bad do you think I screwed up the motor by overheating it? It wasn’t smoking or smelling funny but was obviously boiling internally.

Was my thermostat likely the reason for overheat? I made sure my water pimp was installed the same way it came off and I pulled the outlet hose and what I could see of the impeller was in good shape. I’ll pull it all back apart again but my mechanic had originally told me it didn’t need an impeller and the alarm was only because of a loose belt so I don’t really trust the guy!

I also noticed after sitting when I hit full throttle it steams out the passenger exhaust for about 5 seconds until we get on plane and then it goes away

When you said you put the T stat in facing away from the engine ? The larger part of the thermostat will face the engine . If you put it in upside down it will over heat.
When in doubt YouTube is your friend. The coolant sender is on top of the intake manifold near the distributor.

Yeah I put it in upside down. Once I fixed it it seemed to cool fine but now it’s steaming after I shut it off for a while then go to take off. Afraid I might have fried the motor by overheating it

How hot did you get it? Did you have damage to the rubber exhaust hoses? A little steam is normal especially in cold water. Get the gauge fixed it should run about 160 degrees.

When I stopped I went to touch the exhaust elbows and it instantly burned my hand. It was boiling water inside I could hear it. It was smoking a little out the hose coming from the oil toward the air cooler but not a lot of smoke there. It took about an hour and a half for it to cool down enough for me to attempt changing the thermostat around. Once I flipped the thermo she started back up and we went across the lake and I instantly felt cool water running through it when we got the throttle. At the worst point of overheat I smelled some oil burning (i think it needs a valve cover as this is nothing new it’s done that since I’ve had it), I saw a minimal amount of smoke coming out the rubber tube by the air filter, heard water boiling inside, and I could have cooked a steak on the exhaust.

Some times the 4'' rubber hoses will delaminate and cause a restriction in the hose . Squeeze them and make sure they are solid with no soft spots or remove them for inspection.

Quote:

---

Originally Posted by michael hunter

Some times the 4'' rubber hoses will delaminate and cause a restriction in the hose . Squeeze them and make sure they are solid with no soft spots or remove them for inspection.

---

This is exactly what you need to look at next. I cooked a hose on my boat two summers ago due to a faulty muffler I installed that had a restriction in it that caused pressure to build up and sent all the cooling water to the other side. The exhaust heated the rubber, it delaminated and blew apart on me while at speed on plane. Bad day, anyway, I replaced the hose and still had issues until I figured out the muffler was bad. Long story short, check for restrictions or just replace hoses for good measure.