Engine Running Hot / Gauge Issues??

[viperos]

A couple weeks back I noticed my temp gauge was quite a bit higher than normal. It usually runs around the left side of the "N" of "NORMAL", but now its hovering between the "R/M". When I start the car everything is normal, then about 6-8 min into driving, the gauge goes from the bracket, and shoots to the right side of the "O" in a couple seconds. It never goes above the "M" though. I just replaced the thermostat with a new one, flushed the coolant, and replaced the temperature sending unit in the engine. I just hit 100K miles, so I'm not ruling anything out.. Any ideas guys? Thanks.

 

[revhead347]

That's actually about where it should be running. I'm willing to bet your old thermostat was jammed open, and keeping it too cold. If you still have your old thermostat, you can try and throw it in boiling water to see if it was opening and closing normally.

Kurt

 

[Grn92LX]

Should be tested with a real gauge to know for sure what's really going on.

 

[Bullitt95]

That's actually about where it should be running. I'm willing to bet your old thermostat was jammed open, and keeping it too cold. If you still have your old thermostat, you can try and throw it in boiling water to see if it was opening and closing normally.

x2

 

[Chythar]

Going from "N" to "R/M" in a couple of seconds is not good and can't happen with a correctly functioning system. I believe either the gauge or the sensor (CTS - Coolant Temperature Sender) are bad. You could also have a bad connection between the CTS and its plug. The CTS is on the lower intake, just to the right of the distributor. It looks like a brass plug wit a single 90* plug on it. If you look inside the plug, you'll see two pieces inside. Try to squeeze them together some more, and you might try some electrical contact cleaner. See if that affects the gauge any.

If you have a code reader that can read PIDs (engine sensors), you can read what the coolant tem that the computer sees. This comes from the ECT (Engine Coolant Temp Sender), which is screwed into the metal heater lines on the passenger side of the engine. If the ECT is giving the wrong readings, the computer will not know the engine temperature and add more fuel to bring the engine to operating temp. This usually results in an engine overheating or running really hot.

 

[viperos]

Thanks for the suggestions guys.. The old thermostat was properly functioning (tested it in boiling water), but that wasn't my stock thermostat.. I used to change it twice a year with a 160* for summer driving and track stuff, 195 during winter.. And my engine has always run cool (with both thermostats), both around the lower or upper "N" range respectively.

I'll pull the codes and see what I can find through that avenue, but I did replace the temperature sending unit when I replaced the thermostat.. same problem as before. I'll clean the contacts and go from there.

 

[viperos]

Here's a video of a few weeks ago. This is when it would only jump to the "R" in a few seconds, but it still shows my main problem.. Could it be a bad gauge maybe? I cleaned the metal contacts on the sensor, and it seems to still be doing it.

YouTube - Mustang Temp Gauge