I have an original 1988 Mera. Stock 2.8L V6 Engine. Always ran great no issues. Recently I upgraded to a PISA Euro Dash with aftermarket gauges. I have near everything working with the exception of the temp gauge overheating.

If anyone has seen my posts I even changed the charging dash light to incandescent as suggested. I also have the original oil pressure gauge attached in the glove box and original sender being used until I can make a "T" for both the original and aftermarket sender to be used.

Here is what I have done thus far to address the overheating:
1. Opened all of the caps - fill, radiator, and overflow.
2. I removed the thermostat.
3. I pulled out all of the antifreeze with a shop vac. Then flushed it complete for a long time with water.
4. (Near impossible to get to the drain plug on a Mera due to the front valance)
5. From the fill tube, the water was easily and forcefully coming out of the radiator.
6. This car has about 60,000 miles and there was very little rust and or debris.
7. After the flush, with the vacuum pulling from the fill and all of the water removed, I had hard suction from the radiator.
8. This leads me to believe there are no clogs in the system.
9. With the car on a slope I refilled the overflow first to the proper level.
10. Then filled antifreeze from the fill tube until I saw antifreeze coming out of the top of the radiator.
11. Then topped off antifreeze at the fill tube and closed the cap.
12. Note: I see all of these videos to turn on the engine and look for bubbles.
13. When I turn on the engine I am getting antifreeze pouring out of the fill tube.
14. This leads me to believe the water pump is working well. Also when I squeeze the top hose I can feel fluid flowing.
15. I turned on the heat to allow for antifreeze to run through the core. Then let it cool and topped it off (maybe 1/4 cup).
16. Now I am letting it cool with the back jacked up high to see if this makes any difference. (BTW it did not)

If I drive it around the block without a thermostat it runs up t0 210 + on the gauge. This is another thing not making sense. With a laser thermal scanner the manifold is 140-150, the fill tube is 140, the valve cover is 140 or less. If I put the laser directly on the temperature sender I am getting 215-225 degrees.

Can anyone please explain this or what to do? The 2 wire aftermarket sender must be wired to the signal and another side to ground which does not make any sense since it is attached to the engine but this is what they told me from the manufacturer. I cannot use the old gauge as it is built into the old cluster.

My next step is to install another gauge which wires up normally with one wire to the signal and the sender itself if grounded to the block. Any suggestions are greatly appreciated!

[This message has been edited by jrr (edited 12-11-2025).]

quote Originally posted by jrr: Any suggestions are greatly appreciated!

Paragraphs, my man... learn to use paragraphs.

[EDIT] Much better!

quote Originally posted by jrr: I turned on the heat to allow for antifreeze to run through the core.

Coolant is continually running through a Fiero's heater core.

[This message has been edited by Patrick (edited 12-12-2025).]

To me it sounds like the sending unit and the aftermarket gage are not compatible.

Gages and sending units communicate via resistance values, the two units must have compatible scaling.

What brand of aftermarket gage are you using?

quote Originally posted by jrr: I have an original 1988 Mera. Stock 2.8L V6 Engine. Always ran great no issues. Recently I upgraded to a PISA Euro Dash with aftermarket gauges. I have near everything working with the exception of the temp gauge overheating. Here is what I have done thus far to address the overheating...

What evidence is there of "overheating"? Is coolant puking out of the reservoir?

As posted above, it sounds more like an issue with the sender and/or gauge not working properly together.

You've been jumping through hoops to double-check your cooling system, yet a quick scan would've told you what the actual coolant temperature is as reported to the ECU by the CTS (Coolant Temperature Sensor).

If by some chance there is a problem with your cooling system, These are the steps I take when servicing mine.

[This message has been edited by Patrick (edited 12-12-2025).]

quote Originally posted by Patrick: What evidence is there of "overheating"? Is coolant puking out of the reservoir? As posted above, it sounds more like an issue with the sender and/or gauge not working properly together. You've been jumping through hoops to double-check your cooling system, yet a quick scan would've told you what the actual coolant temperature is as reported to the ECU by the CTS (Coolant Temperature Sensor). If by some chance there is a problem with your cooling system, These are the steps I take when servicing mine.

Yeah... I kind of want to piggy back on this. I went through a ton of hoops to solve a cooling issue. I did end up having a cracked cyl head, which I eventually replaced... but a lot of my problems turned out to be a string of bad coolant sensors... which even includes the CTS. I've got the opposite problem where it shows my car never gets above 100 degrees, when clearly it is.

But yeah, if you have a way to read the ALDL feed and get informationo from the CTS... it'll tell you what the actual temperature is (unless that sensor is bad too, such as in my case, haha).