So I went on a 400 mile trip today in my 1st gen that is new to me and noticed that the temp. would go up just past the first mark (1/4) then back down to just under the mark, moving back and forth basically 1/4 about every 15sec.. It did not stabilize at all, almost like it wanted to over heat but the thermostat would catch it and cool it back off again. Anyone have any ideas I don't think this is normal, I know it doesn't do this on my 3rd gen. Oh and all the fluids are up.

 

My guage did the same thing and i found that it was a loose ground that is on the top of the grille mount just in front of the battery, mine came loose i tightened it up and no more jumpin around.
Hope this helps

 

My ,95 does the same thing. When I inquired on the 2nd gen forum, they said it was pretty normal and had something to do with the placement of the sending unit in relation to the tstat. Maybe it is the same situation.

 

Mine did that too, and I've driven a few other vehicles that did it also. I think it is basically just where the sender is - the coolant temp fluctuating SHOULD be normal, although you might not see it do it on every vehicle.

 

The "rise-drop, rise-drop" is normal for a first gen, but not every 15 seconds...
check your fluid levels and the ground, if tose are good, you might have a bad sender or t-stat..or just an air bubble stuck in there...

But , these trucks are kinda unique, each one behaves a little different, so it may just be normal for your truck....

 

mine did that until i installed a new cummins tstat now its steady

 

There were a number of different t-stats available for this engine. If you are up in MT, you want the slowest acting highest temp one you can get to avaid this problem (slow opening limits the first blast of cold water coming into the engine from the radiator when the t-stat first starts to open, keeping you from having the big hot-cold swings). They also had trouble with air bubles getting caught in the housing, so I believe that the lates model t-stats had three "jiggle pins" to let the air pass through.

 

You said Temp gauge only goes to the 1/4 mark, not the 190. This might be another indication of bad TStat. Get a Cummins TStat, many others prove to be xxxxx.

 

Thanks for the help I will get one first thing Mon. I hope that is it