Are These Temp Gauge Sensor Readings OK? (Page 1/1)
Notorio JUL 11, 02:29 PM
Background: you may recall that the success of my '88 2.8L, 2-year long rebuild (including port&polish heads, port exhaust logs, port intakes, 1.6 rockers, Fiero Store valves, and Rodney Power Pulley, cleaned/tested fuel injectors, etc.) was sullied by briefly connecting the ground wires near the starter to HOT which melted a few wires in my harness. After repairing the harness the car started but ran poorly due to water in the gas. After flushing and 2 tanks of fresh gas with IsoHeet the car runs well except for two lingering issues which I have been loath to address:

1) Dash Temp Gauge slowly goes off scale during warm-up.
2) Engine idles well but SEEMS to have a slight misfire and no power.

THIS POST is only asking for ideas on #1, the Temp Gauge problem. I will start another thread for problem #2 because I feel that they are not related.

Data

a) physical measurement of coolant temp after warm-up and gauge is offscale is 180F, spot on for Rodney's thermostat.
b) The sensor was new for the rebuild, installed with teflon tape (I know), but reads as follows:

o Sensor body-to-ground, 0.1 ohms
o Pin A (Green/White) terminal is 3000 ohms at room temp and 300 ohms at 180F.

I can only find specs for this at 1,365 ohms at 100F and 55 ohms at 260F. If I interpolate between the points to 180F I calculate 250 ohms, which seems pretty close to what it should be. Since that is LOWER then the gauge would read HIGHER, but enough to go off scale?

Before shelling out for another sensor I wanted to solicit your opinions. My worry is that the 'ground short' adventure damaged the gauge.

[This message has been edited by Notorio (edited 07-11-2020).]

theogre JUL 11, 03:48 PM
Never trust a dash gauge.
Must check them using ECM scanner, shop gauges, etc.
If they match then can be many problems like bent pipes, crap in the system, etc.
Air in the system doesn't help and can take several heat cycles to purge. That's assume the overflow tank and tube and Rad Cap are good.

See my Cave, Crushed Pipe and rest of section.
Rebuild engine etc? Can have RTV silicon boogers blocking small coolant passages won't help.

------------------
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

pmbrunelle JUL 11, 06:15 PM
Refer to this chart:
http://www.fiero.nl/forum/A...14-2-119370.html#p17

For more accuracy in using the chart, you can interpolate between adjacent rows on the chart, but the error won't be so bad since the temperature step between rows is small.

The gauge is pretty robust, I doubt it would be broken from your mistake.

I had the same symptom on my rebuilt engine; the needle would go into the red zone while the engine wasn't actually overheating. I know the needle angle (on the shaft) was correct because it pointed towards full cold on a cold engine.

In this thread I described what I did to solve my problem:
http://www.fiero.nl/forum/Forum2/HTML/143983.html

I never really found a root cause.