Engine/Transmission (1994 - 1998) Water Temperature Cycling

[Slow Six]

t-stat

The Napa part number for this is 33039S. Be sure they get the one with the "S" after the number as this denotes superstat. It takes a little getting used to the new temperature range on the guage, but now that I am used to it, I am comfortable running at 195-200 all the time even on hard pulls in warm weather. The fan seems to cycle normally as it did with the 180 t-stats. I tow loads often grossing over the 20,000lbs. and have had no problems with temperatures. Hope this helps.

 

[cclemons]

Wow,i have a 1996 that has never cycled. I was thinking about putting in a hotter stat because I have always thought it ran too cool. It stays about 150-160 unless i'm towing. I have seen it up to about 190 pulling a trailer in the mountains but it has to be a steep climb. I don't want to change out my stat if i'm going to get into this cycling thing.

 

[Ben Rumson]

I dropped a new Cummins 180* stat in mine a week ago and have driven over 1,400 miles since then.



NO MORE CYCLING and it stays a constant 170 degrees. Cab heater works great.



With weather front installed, I got 23. 6 mpg from Logan, Utah to Casper, Wyo. on New Year's Day. Roads were ICE - Lots of wrecks. "cooler" stat has NOT affected mpg. Return trip netted 24. 2 mpg. Both trips running #2 Diesel and 4oz of Howe's per fill-up.



I couldn't be happier with the new stat. Yes, the cummins "tollerates" the cycling, but it is an added stress to the head gasket - even if it does tend to do alright in spite of the temp cycling.



For less than $25 bucks, I eliminated the cycling and no longer have to "hope" the cycling's not affecting the head gasket. Now, I truely don't have to concern myself with it. It's no longer an issue - period.



Cummins p/n 3928499 180* t-stat.

 

[bmoeller]

Mine only seems to do it when it gets below 50-60*. I've checked the coolant temp with a thrmometer and when the gauge says 190* the temp in the radiator says about 130-140*. I've tried several new t-stats and they all do it. Got a new Cummins t-stat but haven't gotten around to trying it yet.

 

[Stixx]

The only time my stops cycling is when I pull heavy loads. That is when I know its starting to run hotter then normal.



Every 94-98 12v I've been in does cycle .

Some drop more then others or some not as much.

But they all cycle.

 

[vssman]

I just replaced my original t-stat with a Stant 180* listed for the Cummins. It fluctuates WAY to much 215 (one needles with below the last white line on the hot end) down to 145 (just below the white line on the low end). It's 15* outside today so the coolant is going to be cold, but... It's being replaced by a Cummins stat.

 

[Ben Rumson]

Originally posted by vssman

... It's being replaced by a Cummins stat.

There's no guarantees that it will stop the fluctuation entirely, But mine HAS and I'm very glad I switched it out.



I hope your results are as good as mine !



Keep us posted.

 

[vssman]

Well, I've finally replaced the stant tstat P/N 14248 with the revised Cummins tstat P/N 3934373 and completely eliminated the cycling while still having heat. Also, the jiggle pin worked when I installed the cummins stat (I could hear it jiggle while I filled the radiator). I noticed the cummins stat looks like it will flow much more water than the aftermarket. Sooo, I'm warm but a bit poorer than if I just used the aftermarket stat. Thanks for your help in my other post "Air bound cooling system"

 

[Ben Rumson]

Glad to hear it did the trick !



Thanks for keeping us postal... oops, I mean "posted".