Hi everyone...new member who finally got his hands on his high school dream car, 1988 GT (manual with T-tops) with 3,900 miles on it!
For the past 5 weeks of ownership I have been trying to get her to run cool and it's a mixed bag. I've replaced the Temperature sending sensor in the block (because I broke the connector taking it out) and then replaced the fan temp switch with a RD 195 degree unit. I have burped the damn car more than a newborn and the result is...sometimes it runs 240 plus and sometimes it runs at 200.

I have not replaced the coolant yet, only topped it off when I got the car. It looks good, but there could be crud hiding in the radiator. I checked the lines under the car and they are not dented at all. The fan will not come on when the temperature goes up (before I changed to the new lower temp switch and after) The fan will come on if I turn on the AC so I know the fan actually works.

The car is essentially new in that it is unused, but it is 36 years old with limited driving. Any tips from the initiated would be greatly appreciated!!!

Is the engine puking coolant into the reservoir when it's "overheating"? If not, the temp gauge (or the new sender) is probably misreading the temperature. What temperature is the ECM seeing (as reported by a scan tool and/or WinALDL?

Have you tried running the car with the thermostat removed? Could be stuck closed.

I would bet on the temp sender or the gauge, mine misread horribly high until I fixed GMs wiring mistake and wired the bulb test to the bulb instead of the gauge, and recentered the gauge. (All the bouncing back and forth on start up shifted it's "center"off center, I got it centered correctly and it reads correctly) I don't know if the latter gauges have the same problem (they automatically reset every time they're turned off) but that permanently fixed it with my early gauges.

The engine is puking coolant back into the tank. I have not run the car with the thermostat removed. I have rewired the temp gauge to eliminate the pegging issue (both at the cluster and at the thermostat)
I do not have any testing equipment as of yet...but the more threads I read, the more it seems that I need them.

In all of your experience, is it possible that the water pump could just be rusted away from sitting for 36 years with so little run time and that it just isn't pushing the fluid the way it needs too?

quote Originally posted by Profasr: I have burped the damn car more than a newborn and the result is...sometimes it runs 240 plus and sometimes it runs at 200.

As much as I enjoyed your description , it tells us nothing as to your actual method.

quote Originally posted by Patrick: I've used the following procedure with half a dozen different Fieros (running a Stant SuperStat 195° thermostat and a 210° on and 200° off fan switch) and never had an overheating issue...

quote Originally posted by Patrick: * Make sure rad cap is the proper one for Fiero use. The catalogs are wrong! You want a non-vented cap. * Check that the overflow tank and the small hose to the rad are both in good shape. Otherwise air gets sucked in. * Ensure that coolant level in overflow tank is at the "Cold" level. * Position rear end of Fiero higher than the front. * Remove thermostat housing cap and thermostat... and then add coolant to thermostat housing with rad cap also removed until coolant runs out the top of the radiator. * Re-install rad cap. * Continue to add coolant until you see the level come up to where the thermostat normally sits. * Put thermostat cap on and turn just barely enough to hold cap on. * Start engine and run for about 30 seconds. * Remove thermostat cap and check coolant level. * Repeat last four steps until coolant level no longer drops. * Re-install thermostat and thermostat housing cap. As long as there are no blockages anywhere in the cooling system and the water pump is circulating coolant, you should be good to go.

quote Originally posted by Profasr: One more thing, if I turn the heat on it does cool the engine right down very quickly. This is fine as it's still cool in the North East, but it's going to suck in about 3 weeks...

If that little heater core cools the car down, I would suspect that your radiator is full of sludge, or you have a radiator hose that is delaminated and closing off water flow.

Feel the inlet (driver side) and outlet hoses (passenger side) and let us know the difference.

[This message has been edited by olejoedad (edited 05-05-2024).]

Yes, correct rad cap is a must.
See https://web.archive.org/web...erocave/coolcaps.htm

Don't trust the dash gauge. Get a ECM scanner or other way to get correct temps.

Pipes may not be crushed but still have crap plugging the rad etc.
Rad plugged is easy to check using IR thermometer & look @ bottom & top tubes.
Bottom tubes often will get plugged first then doesn't do anything & stays cooler then top tubes.
If "dirt" is blocking, flush may help but plugged Aluminum Radiators often means tubes are "rust" plugged & any method of flushing won't work.

When filling after flush etc, Do Not use Premix coolant.
See https://web.archive.org/web...erocave/coolfill.htm

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave