Question is about my 1999 7.3 with 256,000 miles. Everything is stock except for gauges and heavy duty torque converter and transmisison.

I noticed today that instead of a normal slow and steady rise of the in-dash temperature gauge going up to where the needle touches the "waves" under the little icon that the guague started moving up, stopped a little short (cool) from where it normally has always stopped, then went up to the top of the temperature icon then as fast as it went up it fell back down to a smidge below the little waves under the icon. This is not normal behavior for this vehicle that I have ever seen in the last 7 years.

Is this a thermostat beginning to die? Heading out on a 1k mile trip and hate to get stuck somewhere.

Your thoughts please everyone.

Thanks,
Medic66

 

If its an A/T don't even consult that gauge. You need to test the system to determine if everything is A-Okay.


If a M/T you can use a Scantool to monitor the PID.

 

I believe you are referring to tranny right? My apollogies as I am referring to engine temp gauge. I did not specify that the first time. Sorry!!

 

what Pirsch means if your trans is the auto the temp gauge gets its reading from a sensor located on the trans, and you want to test the system your self, if standard (hand shaker) you should be good to use a scan gauge or similar tool to monitor the temp sensor as its a different location then the auto


That is what I am understanding for his post

 

I.believe you.are.right and I.should.have.done a.better.job indicating that my question was about.the.engine.temp and.not.the.tranny temp. My bad!

 

Check the 42 pin connector that jumps from the chassis to the engine on the driver side below in intercooler tubing. My connector chaffed the wires on the valve cover and it rubbed through the wire for the coolant gauge.

 

Just to expand on what Jaimie said. On auto transmission trucks of our vintage there is no coolant temperature sensor installed from the factory, a lot of us use the EOT to check and see how hot things are getting under the hood. There is not a lot of difference, usually, between EOT and ECT.

If; however, your truck is a standard / stick shift, then the factory does install an ECT, which of course can be read and used to monitor temps under the hood.

 

Not to mention the stock Coolant gauge is not a true gauge in that it's more of a idiot light......It's either go or no go....there is no gradual ramp up.....

 

This is exactly what I meant to convey. I apologize as I was in hurry and should had waited until I could have written a more accurate paragraph.

 

So to review, the automatic transmission equipped trucks (and if he has a torque converter, his is an automatic), do not actually have a sensor that reports coolant temperature directly to that gauge. The PCM uses an algorithm to obtain that number and represents it based off of a few things which include the engine oil temp. Engine coolant temp and engine oil temp should be fairly close if all things are working properly.

 

No problem, I got you brother! 😉