Dash engine heat gauge


Asked by Dec 12, 2014 at 06:57 PM about the 1987 Pontiac Firebird Trans Am GTA

Question type: Maintenance & Repair

after 5 blocks engine gauge reads 190 and then it goes to 260 for about 3 blocks and
GTA 350 5.7 1987
After 5 blocks engine gauge goes to 260 red line
then it drops back to 190deg  and I have no problems with it all day after that
sometimes it goes to 230 and then drops back to 190 and all is ok.
I have changed all the sending units ,and have gotten out of the car when it says it is hot and it is not hot .And the fans are working.
This is pretty much the gauge sending the wrong message......I think.

8 Answers


So you need to consider changing the temperature sending unit.


Looks like this http://www.rockauto.com/catalog/moreinfo.php?pk=1393291


I changed both sending units computer 2 wires and engine engine unit 1 wire. Still have problem.


Ok, so it sounds like a sticking thermostat. The engine keeps getting hotter until the thermostat finally opens up and then the rest of the day it works. I used to have that in the motorhome when I just ran it once a week in place. I'd keep staring at the temperature gauge while it got closer to the Hot, then the thermostat would finally open.


Changed thermostat twice. I do not think the engine is over heating,just a bad reading .. but why? How can I check temperture,with out depending on gauge?


I have no idea. I have a laser thermometer that I've only used to shoot the front and back of catalytic converters. I imagine if I had the same problem I could shoot the radiator, heads, freeze plugs.....


Sending unit varies resistance to ground as temp changes. If you know your not overheating then I would assume that the wire is shorting to ground somewhere giving you the max reading. Inspect the wire especially arround the manifold/header area and repair if required.


That sounds like a area to look at.....will give it a try. Thanks

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