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Discussion Starter · #1 ·
I have a 1999 cummins and have replaced the thermostat with a cummins. Pulled the rad and cleaned. Clutch fan is working. In the last seven years the temperature has not gone past 90 degrees even when pulling a load. The guage now moves up to 90 running empty and then slowly drops even going up hills and keeps moving. Is this normal? I have been to three diesel mechanics with no diffenate answer but to say the old thermostat must have not been closing all the way.

Thanks Wayne.
 

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Do you mean 190, and when you say it then slowly drops, just how far does it drop and does it stop dropping somewhere. Its normal for the temperature to rise to the degrees that the thermostat is set for ( like 190*) and then it'll move up or down a little bit according to load/ demand on engine, the outside temperature, etc. As long as its warmed up and doesn't overheat its OK. The thermostat is a simple, ignorant little mechanism, just keeps on doing its job, opening and closing that's all.
 

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I had a 97 gasser, when i put it in you could notice the ttemp bouncing around more than normal. It settled down eventually. It would get up to about 190, then drop about 50 degrees or so, then warm back up, then fall again. My guess is the new thermostat is just "breaking in", and i use that term loosly. Mine settled down and i would just keep running it. Just makes sure to keep a close eye on that temp gauge.
 

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Discussion Starter · #4 ·
I have the stock guage which read 60 cold 90 half way 110 red hot. I ran the truck for sevens years and the guage would sit between 60 and 90 even with the camper on. Now with the new thermostat (and old one once it started acting up) it goes up to 90 then slowly drops down to between 60 & 90 sits there and slowly climbs back up to 90 and back down running on the flat or on a hill. Running with the camper on now it goes between 90 and the first white mark. Is this normal?? This will drive me crazy!!
 

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Fill out your sig, and location (guessing your in canada and those are celcuis temps???)

You could swap out this thermostat and see if it changes....
 
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