My temp gauge runs back and forth from 190 to around 160.Do you guys think the thermostat needs to be replaced or the gauge?Thanks<br>Steve

 

Sounds about like mine. I have never seen over 190 on my guage. 160 is about where it runs if I am just loafing along not pulling. If you do have a problem, so do I. Anyone else?<br>Ed

 

Your temp should fluctuate a little, as the engine is warming up, but should stabilize after the warmup period (which may vary in length). Yeah, I know that's vague, so I'll say some more.
When the thermostat is closed, the engine water should heat up, this time to heat up will depend on how the engine is running, driving or idling. Once the engine gets to the temperature where the thermostat is supposed to open, the thermostat opens and a rush of cold water enters the engine. When this cooler water hits the thermostat it closes partially, or more. The hot water in the radiator now cools, but not down the temp of the water that was in there (ambient temp), before the water in the already-warm engine gets up to the temp the thermsotat needs to open. This cycle will continue until the temperature stays high enough at the thermostat to keep it open (&quot;open&quot; can be partially or full open).
Keep in mind the thermostat has one temp where is is supposed to open, your gauge may be all over the place but that doesn't matter.

So, taking all of that into account, some fluctation is normal, especially with the size of the cooling system on these trucks.
You should worry when the gauge goes over 190 and drops like a rock (thermostat stuck closed), or when the gauge never comes up (thermostat stuck open).

Hope this makes sense.

Chris

 

mine runs exactly the same....190-160.....my uncles 94 12-valve ran the same also ( actually his didnt get over 180, maybe the 24 valvers run a tad warmer)

 

Mine does the same thing, too. That is a normal thing for these engines.<br>If you don't like it, you could replace the thermostat with a genuine cummins<br>part, #3934373. That will stop the fluctuation. I replaced mine with this<br>new part, but it seemed to take longer to come up to temp, and didn't get<br>over about 180*. I put the old one back in, and now have a spare, I guess.<br>I just close off the air flow through the radiator, in cold weather, to slow<br>down the cycling. As far as I have been able to tell, it doesn't hurt anything.<br><br>Hope that helps... Oh, and welcome to the site.

 

Thanks for the help guys.Im glad I found this site.

 

I also replaced mine with thew part mentioned above- slower warm up and stays at a constant 180.<br><br>Mike