Mine does the same thing temp goes to 190 for several seconds then drops to 140, will soon get a thermostat from Cummins

 

i havent been worried about mine to much yet but as soon as i get my work bench of cummins parts installed ill get a t-stat from cummins

 

i have been told this is normal. Normal fluctuation is 60* on the cooling system. if it is 20* out side my truck will climb to about 220* then down to about 160* until it fully warms up then is changes very lil like 20* had someone from cummins tell me this is acceptable. i am not saying your truck is fine but i am not saying its not. Just letting you know what i have been told.

 

I still have the factory one in my with 241,xxx miles. the first time it opens is around 220 to 230 then drops to about 150. then back and forth from 150 to 190

 

For some reason right after I bought a new one the one I have it it started working normally... So i've got a spare if it starts acting up again.. Thanks to all for your help!

 

NOw, for some reason I remember seeing a post where a little piece of rubber worked its way into the thermostat mechanism and prevented the thing from opening and closing. Sometimes, you got to r&r it to see whats happening.

Glad you got it fixed - got to love things that fix themselves.

 

x2

 

x3, also if you look at the cummins or mopar thermostat the inside part is lined with a rubber like coating. this coating was breaking down and flaking off. good chance thats where rubber came from. the rubber is there to try to make the stat not be so sensitive. so that can also contribute to fluctuation if gone. btw the newer design still uses the rubber coating but updated to prevent material from flaking off.

 

Yes, thats what I was talking about - been a long time since Ive seen it though.

 

well I got my $42 thermostat and gaskets Friday but after doing some searching I see that they gave me the old style thermostat, should I go ahead and install it or return it and get the newer style?