Engine/Transmission (1994 - 1998) Temp Gauge acting funny

[Cumminsman12]

So I have replaced two freeze plugs and fixed a head gasket leak in my 97 with the 93 engine. I refilled the coolant system with Heavy duty precharged antifreeze. Now the temp gauge is hunting for temp. When I say hunting it is swinging. I know it is not the head gasket, this happened to the original head gasket on the original engine and the gauge still did the same thing. I was wondering could this be contributed to the fan, or the tstat, or maybe the radiator cap? The temp never goes above 190 and never below 160 when I am driving highway speeds. When I am idiling the temp gauge does not swing and stays right at 180. I am so confused. I know when I go to check my antifreeze I have not lost any and both the radiator and coolant overflow bottle are full. The system is not pressurizing to the point that coolant is blowing out of the overflow bottle like the old engine did. What could be the cause? I put 150 miles on the new engine and am nervous. Just want the truck to be right before I take it on any trips with the boat or the camper this summer. Any help would be appreciated. I have tried searching the forum but the search option does not seem to be working on this computer.

 

[Missouri Mule]

Temp swings are normal on the 12 valve engines especially if your using original t-stat. Your tempature readings seem to be normal.

There is a newer t-stat that doesn't swing as much out. I still have may oringinal t-stat and if it is not swinging something is wrong.

 

[BDaugherty]

I agree with the above. Swap in a new quality T-stat such as the one from Cummins. Also, make sure all of the air is out of the system.

 

[GAmes]

It is an internet myth that there is a new t-stat that won't swing. Every now and then you will find one that doesn't swing, but it will be the same PN of the ones that do swing. The one I have currentlt installed will stay steady one day and swing the next. I haven't figured out why, but I'm not concerned. The wobble valve located near the t-stat (has a small s-shaped hose on it) automatically purges any air from the system. No special procedure required, just drive it.

 

[KBurgoyne]

i can watch mine go up and down on the freeway as long as the temp is below 60. its not a problem it just serves to remind you that you dont have an EGR. so its a good thing.

 

[Cumminsman12]

i can watch mine go up and down on the freeway as long as the temp is below 60. its not a problem it just serves to remind you that you dont have an EGR. so its a good thing.

Haha I agree with that, No egr no problem and I did replace the tstat and no change. I was out getting firewood the other day and got stuck in about 3 feet of snow on the side of the road. I had to get on her pretty hard to get her out and when she finally came out, the truck wouldn't heat up. The Tstat was stuck open. Still didn't stop the swing but as you guys have said I am not worried about it. I am just going to drive the truck. The swinging is more annoying than anything. Thanks for the help.

 

[BigPapa]

It is an internet myth that there is a new t-stat that won't swing. Every now and then you will find one that doesn't swing, but it will be the same PN of the ones that do swing. The one I have currentlt installed will stay steady one day and swing the next. I haven't figured out why, but I'm not concerned. The wobble valve located near the t-stat (has a small s-shaped hose on it) automatically purges any air from the system. No special procedure required, just drive it.

There's your correct answer. I thought this was covered in the "12V Engine and Transmission Frequently Asked Questions" section but surprisingly it's not.

 

[Shadrach]

Cummins does make a "slow cycle " stat that doesn't open as fast therefore slowing down the rush of cold coolant coming into the engine. It is p/n 3934373. The stock one is p/n 3928499 with the rubber wrapped around it or p/n 3864178 w/o the rubber wrapped around it. In any case you will also need rubber seal p/n 3925466 & 3927305. All are 83*C or 180*F. These will only work in the 94-98 12 valve engine as they are non vented stats and use the check valve and hose as GAmes stated above. All other stats use in the B series engines are vented and come in different diameters depending on the generation. Some people don't like to see the gauge swing back and forth. The only real problem is in cold climates when your all of a sudden have not heat in the cab because all that cold coolant just moved in.
Shad