85 2m4 SE / 2.5 Temperature Issues (Page 1/2)
82-T/A [At Work] NOV 11, 07:16 PM
Hey guys, some quick questions on my daughter's 2.5 Iron Duke engine.

We've been driving it around lately, but the temperature gauge on the gauge cluster is totally crazy. It shows the car as overheating extremely... like at all times.

When I start it up, the temperature gauge almost immediately goes to the middle, and then sits well past the red into the black area. It freaked me out at first, so I bought a laser-temperature reader. I tested it on my forehead which gave me a perfect 98.6 degrees.


After thrashing the car... and driving it pretty harsh... here are the temperatures:


All temperatures are in Fahrenheit. I just want to make sure I'm not crazy, and that it's just the gauge (I think it's the gauge).


- Starting from the left (the thermostat housing), the temperature is anywhere from 185-199 degrees. I am running a Stant 195 degree thermostat.
- At the intake manifold, it's typically around 155 degrees, sometimes gets up to 160 degrees.
- In the middle, RIGHT where the exhaust manifold bolts to the cyl head, it's typically anywhere from 235 (coldest after warmed up) to 265 at the hottest. Just a little further back, directly on the manifold, it's around 325 degrees.
- Below the Oil Fill on the passenger side of the cyl head, when I point the laser directly at the freeze plug, I'm getting usually anywhere from 200-220 (usually closer to 220).


These temperatures seem pretty decent. I do not know the condition of the radiator, other than it's not leaking. But everything from the middle of the car back has been replaced... so I still need to change the front heater core hoses, the two radiator lines, and probably flush the radiator. I used some cheap green anti-freeze in this engine while I'm attempting to break it in (doesn't even have 10 miles on it yet).

My guess is that the temperature gauge is completely broken... but I'm not sure WHY... so I'm trying to diagnose that. My tachometer is also messed up... but the oil pressure and speedometer are both working well.


Thank you!!!

[This message has been edited by 82-T/A [At Work] (edited 11-11-2024).]

82-T/A [At Work] NOV 12, 08:02 AM
Also... can you guys confirm that the coolant comes in FROM the drivers side (thermostat side). I would hope so, since that coolant appears to be much cooler... while the passenger side (exit at the water pump) appears to be hotter. I don't even know what to think if you guys tell me it's the other way around...
1985 Fiero GT NOV 12, 10:44 AM
Of all the gauges, I have found the temp gauge the most inaccurate, I had similar readings, until I fixed the "bulb test" wiring, and cycled it a few times by grounding the wire at the sensor to the engine. With the early gauges, it seems the "operating range" can get shifted left or right from frequent/very quick cycles, so basically gauge is supposed to read between 0-100 (fictitious numbers) but instead reads between 50 and 150, the needle is still attached as normal, but seems to have "moved". Be careful when grounding the plug, as if you ground it a few times in quick succession (wire slips on the block, something like that) the gauge will pin itself way up at the top (operating range has changed to 250-350 in our fictitious scale, aka all the way up).
82-T/A [At Work] NOV 12, 11:56 AM

quote
Originally posted by 1985 Fiero GT:

Of all the gauges, I have found the temp gauge the most inaccurate, I had similar readings, until I fixed the "bulb test" wiring, and cycled it a few times by grounding the wire at the sensor to the engine. With the early gauges, it seems the "operating range" can get shifted left or right from frequent/very quick cycles, so basically gauge is supposed to read between 0-100 (fictitious numbers) but instead reads between 50 and 150, the needle is still attached as normal, but seems to have "moved". Be careful when grounding the plug, as if you ground it a few times in quick succession (wire slips on the block, something like that) the gauge will pin itself way up at the top (operating range has changed to 250-350 in our fictitious scale, aka all the way up).




Interesting... thanks 85. I noticed just today though when I turned it to the on position, it was drop-dead in the far left, right at the first mark (100 degrees I guess)... it then climbs really fast to 220... which just seems imposible. Like, I start it, and within seconds it's already at the half-way point.


Insofar as the actual temperatures I recorded with the laser temperature reader... does those temperatures look OK to you?
1985 Fiero GT NOV 12, 12:04 PM

quote
Originally posted by 82-T/A [At Work]:
Interesting... thanks 85. I noticed just today though when I turned it to the on position, it was drop-dead in the far left, right at the first mark (100 degrees I guess)... it then climbs really fast to 220... which just seems imposible. Like, I start it, and within seconds it's already at the half-way point.


Insofar as the actual temperatures I recorded with the laser temperature reader... does those temperatures look OK to you?



Yeah, perhaps the sender is bad, or a different ohms range or something, definitely something unusual there, I don't know what the temps should be, but seems pretty much normal.
Patrick NOV 12, 03:38 PM

quote
Originally posted by 82-T/A [At Work]:

Also... can you guys confirm that the coolant comes in FROM the drivers side (thermostat side). I would hope so, since that coolant appears to be much cooler... while the passenger side (exit at the water pump) appears to be hotter. I don't even know what to think if you guys tell me it's the other way around...



I don't understand your description... but from what I understand, coolant flows up through the thermostat and out of the thermostat housing.
82-T/A [At Work] NOV 12, 06:21 PM

quote
Originally posted by Patrick:

I don't understand your description... but from what I understand, coolant flows up through the thermostat and out of the thermostat housing.




I'm very confused then... because the temperature of the coolant LEAVING my engine (out the drives side) is cooler than that which is coming INTO the engine from the radiator via the passenger side.


Can you look at the image above... does this look normal to you? These were the temperatures that I took with my laser temperature reader... thank you.
Patrick NOV 12, 07:57 PM

quote
Originally posted by 82-T/A [At Work]:

I'm very confused then...



Let's get some more opinions on which way the coolant is supposed to be flowing at the thermostat housing.

Is there any way that your belt/pulley modifications have now resulted in your water pump being spun in the reverse direction? (I can't refer back to your photos at the moment.)
82-T/A [At Work] NOV 12, 08:15 PM

quote
Originally posted by Patrick:

Let's get some more opinions on which way the coolant is supposed to be flowing at the thermostat housing.

Is there any way that your belt/pulley modifications have now resulted in your water pump being spun in the reverse direction? (I can't refer back to your photos at the moment.)



No, the rotation is completely stock to an 87-88 Iron Duke, it's just missing the belt tensioner... which just loops it around the tensioner, otherwise exactly the same. It hasn't slipped once either, even when I really beat on it. Of course, it's a new belt, so I'm not leaving it like this. I'll eventually install a solid idler pulley in the same place as were the factory belt tensioner would be, I just haven't done it yet.

I'm going to grab the service manual and see if it shows the direction of flow.


Thanks!
Patrick NOV 12, 08:53 PM
According to this diagram... yes, coolant flows out of the thermostat housing hose.




Obviously not a Fiero engine... but same principle.

[This message has been edited by Patrick (edited 11-12-2024).]