So I have a 1988 Fiero with the 2.5 in it. I recently replaced the head and the water pump the thermostat and multiple hoses. I've run water through the entire system and it's completely clear. I've replaced all the coolant sensors and caps. I've got a new water pump pulley a new cooling fan controller and everything. But the temperature gauge still gets up to just beyond the 220 mark. Also I pressure tested it and she won't hold 20psi but it holds 15 just fine. I'm just completely stumped on what else it could be. Any ideas would be greatly appreciated.

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Joshua Seeger

Don't trust the temp gauge. Is the coolant reservoir puking out coolant?

quote Originally posted by LS4FieroGuy: Also I pressure tested it and she won't hold 20psi but it holds 15 just fine.

Considering that the Fiero rad cap is designed to hold 15 psi, that's fine.

quote Originally posted by LS4FieroGuy: I've got a new water pump pulley a new cooling fan controller and everything.

So... the ECM is not controlling the rad fan?

[This message has been edited by Patrick (edited 11-20-2024).]

quote Originally posted by Patrick: Don't trust the temp gauge. Is the coolant reservoir puking out coolant? So... the ECM is not controlling the rad fan?

The reservoir is not puking out Coolant.
And correct the ECM is not controlling the cooling fan I have a separate system controlling it.

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Joshua Seeger

If you're only going by what the factory temp gauge is displaying, and there's no other evidence, the engine is probably not overheating.

WinALDL and/or a scanner would tell you the actual coolant temperature as reported to the ECM.

quote Originally posted by Patrick: If you're only going by what the factory temp gauge is displaying, and there's no other evidence, the engine is probably not overheating. WinALDL and/or a scanner would tell you the actual coolant temperature as reported to the ECM.

Is there any way to get live data on the Fiero?

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Joshua Seeger

quote Originally posted by LS4FieroGuy: Is there any way to get live data on the Fiero?

I just told you.

Use an IR temp gun on the thermostat neck/discharge hose to see what the temp is coming out of the engine.

I think stock the 88 2.5 ecm kicked on the fan around 230 degrees.

Fiero temp gauges are notoriously inaccurate, so it it best to know the temp of the engine, and where the needle is on the gauge (wherever it may be) and then you have an idea if it is reading "normal" or abnormal on any particular day.

quote Originally posted by Patrick: If you're only going by what the factory temp gauge is displaying, and there's no other evidence, the engine is probably not overheating. WinALDL and/or a scanner would tell you the actual coolant temperature as reported to the ECM.

I've done exactly this for a similar reason and the resultant data showed the coolant temperature was NOT over-temperature.

Software and instructions on how to build your own cable although I believe I bought my cable.

https://winaldl.joby.se/

quote Originally posted by Patrick: I just told you.

So I just downloaded that software to my laptop and then hook it up to my Fiero?

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Joshua Seeger

quote Originally posted by LS4FieroGuy: So I just downloaded that software to my laptop and then hook it up to my Fiero?

Yes... but of course you'll need the appropriate ALDL cable. A couple of options Here...




...and Here.




There may be others. Perhaps contact whatever supplier you choose just to make sure the cable and software will work with an '88 duke. I seem to recall there were some hiccups with the '87 duke and WinALDL.

quote Originally posted by LS4FieroGuy: So I just downloaded that software to my laptop and then hook it up to my Fiero?

Yup, when I did mine (years ago) I had a nice little XP Netbook with a car charger. Drove around with the Netbook connected, took a lot of data.