Temperature Guage

[Onebigcanuck]

Well, for what ever reason my temp is getting cooler by about 23 degrees F and than going back up to 212F (100C) where it stays for a while before dropping one hash mark again (23 degrees). This happens at highway speed or in town. in the past 4 years it has always warmed up to the centre hash mark (100C) and stayed there.

While pulling it stays right at the centre hash mark (100C)

Anybody got any ideas ???

[killerbee]

Well, for what ever reason my temp is getting cooler by about 23 degrees F and than going back up to 212F (100C) where it stays for a while before dropping one hash mark again (23 degrees). This happens at highway speed or in town. in the past 4 years it has always warmed up to the centre hash mark (100C) and stayed there.

While pulling it stays right at the centre hash mark (100C)

Anybody got any ideas ???

your report is what I see a lot of. The section of the gauge you are referring to is as little as 7 degrees between tick marks. So it is misleading. Just disregard it .

[Onebigcanuck]

I guess what I should have said for Heavy Hash Marks ( 3 smaller in between).

Help ???

[JohnC]

Other than gauge issues, there are really only 2 causes for that behavior. One is a sticky or sluggish thermostat; the other is an air lock in the system.

[killerbee]

I didn't think of that. A trapped bubble could do that.

Good post John.

There is a screw on top of the stat housing. With the motor running, loosen it till water runs out.

[Inspector]

My dash gage is usually half a needle on the cool side of 210F when warmed up and stays there. On the Attitude it will read (no load) anywhere from 192 to 194 depending on ambient temp and can be a bit higher. When loaded (towing) the gage will not move from the 210 hash mark except under extreme conditions and then it will sometimes go to 230-240. The attitude reading will read (while towing) 192 to 215 (normal driving while towing). The fan will engage anywhere from 198 to 205 and cool down to 192-194 and cycle off. Under extreme towing conditions (a grade) the temp reading on the attitude will go to 230 but the fan is fully egaged and will begin to drop the temp.
The allison has taken care of the shifting and all is well.
I guess what I'm trying to say is the dash gage is for reference and to take up space. The attitude takes its reference from the ECM and in my opinion is an accurate or more accuate reading.
Denny

[Onebigcanuck]

Tried the air lock solution. Nope was not that.

[CoachWagner]

Maybe you have the overflow tank cap problem that I have? Check your upper rad hose when cooled in the morning to see if it is collapsed. I was getting these weird temp changes as well. See my post of weird rad hose and the article killerbee posted - it is awsome!

[Onebigcanuck]

Checked the hose this AM and no problem there. When I squeezed it you could see the level in the tank come up a little.

Getting to be a bummer.

[Rabbler]

I would lean towards one or more bad thermostats.
There are 2 in there (a primary and a secondary) and they are both multi stage to help engine reach operating temp faster. Both stats are under the same housing.