The heater shouldnt have any effect on it. Ive had cars that ran borderline hot, and turned the heater on full and it was just enough to aid the cooling so it didnt overheat.

quote Originally posted by Meatstick62: The wierd part is that it seems to be running too cold. After a 30-45 minute drive, it never reached operating temp and never stayed above 180 for long. On the highway or at any decent speed the temps would fall below 160 degrees and never go higher.

What temperature thermostat do you have installed? 160-180-195?

It's also possible that the thermostat is stuck open, or that the "arms" have collapsed and the thermostat isn't seated properly.

The heater core is always supplied with coolant so if you are feeling heat from the vents check the air diverter door. You could be getting some unwanted air movement through the heater core.

I installed a 195 degree tstat. The arms on the tstat are ok and it's sitting in there snuggly.

Where is the air diverter door?

quote Originally posted by Meatstick62: I installed a 195 degree tstat. The arms on the tstat are ok and it's sitting in there snuggly.

I suspect your thermostat is stuck open then, although if you're basing your readings on your temperature gauge (as opposed to ALDL or a scan tool) the temps could be way off.

quote Originally posted by Meatstick62: The wierd part is that it seems to be running too cold. After a 30-45 minute drive, it never reached operating temp and never stayed above 180 for long. On the highway or at any decent speed the temps would fall below 160 degrees and never go higher.

[This message has been edited by Patrick (edited 09-08-2012).]

All the Fiero gauges are notoriously wrong. Always compare the readings to a test gauge.

quote Originally posted by Meatstick62: I installed a 195 degree tstat. The arms on the tstat are ok and it's sitting in there snuggly. Where is the air diverter door?

It's in the air box up front by the heater core. Check out this thread where people have found trash blocking their core. https://www.fiero.nl/forum/Forum2/HTML/124499.html

When you switch from cold to hot do you hear the door move? Mine makes a "clunk" when I hit the stop at either full hot or full cold.

quote Originally posted by rogergarrison: All the Fiero gauges are notoriously wrong. Always compare the readings to a test gauge.

Yes Never trust dash gauge...
Use thermometer, IR ones are cheap, on Tstat housing or scan ECM to get a good reading.

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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 (It's also at the top and bottom of every forum page...)

I'd say that maybe the dash gauge isn't reading correctly, but whenever it reads low the engine pops and gargles when shifting as if it were running rich (and cold).

I have an IR thermometer that I'll try to use on the tstat housing and compare those measurements to the dash gauge. The car is still running pretty cool. On a 10 minute drive this morning in 60 degree ambient temperature air the gauge didn't reach much above 180 degrees.

[This message has been edited by Meatstick62 (edited 09-10-2012).]

Just an update for those who helped or may have a similar issue:

The car is running fine now and I was able to confirm that the gauge is reading fairly accurately by using the IR thermometer. I also verified that the T-stat opens around 195 by boiling it in a pot of water and watching it open. I replaced my incorrect coolant expansion tank with the proper OEM one and drained and refilled drained the cooling system making sure to follow all of the advice here and in the Ogre's cave. I think that my original issue might have just been that the system wasn't fully burped of air. The car gets up to about 200 on my morning commute (we've had some cool mornings here in OH this past week) and it will sometimes reach 220 if stopped at a light or on a longer drive. I only saw the gauge go over 220 once and the most it ever reach was maybe 230 (the fans may or may not have kicked on).

quote Originally posted by Meatstick62: I think that my original issue might have just been that the system wasn't fully burped of air.

Thanks for reporting back.