I replaced my head gasket about six months ago, and after that my engine temp gauge rocks back and forth over the 190 mark. And its not just the gauge, cuz you can hear it in the engine also. Ive also replaced my thermostat after i seen that happenin, let me know if ya have any ideas.

 

The cooling systems are larger then they have to be on these trucks so when they are not under heavy load the gauge fluctuates as the thermostat opens at 190 and dumps some cool water and quickly closes again. This is normal and nothing to be concerned about.

Some guys will opt to put a 180 thermostat in to stop some of that needle jump but truthfully these engines run a little better on the warm side in my opinion. If you find you can't wrap your mind around that jumping gauge, get the lower thermostat

 

Make sure the radiator is clean. Mine rocked quite a bit until I cleaned out the rad due to accumulation from the puke bottle.

 

thanks for the info, just makin sure that it wasn't anything serious or harmful

 

I would only be concerned if my temp gauge didn't fluctuate.
Put the truck under the load that it was designed to be used for and the needle will hold steady.
Cummins/Dodge got tried of fluctuation complaints and in 1998 electronically changed the gauge into an idiot light.
The temps still fluctuate, you just can't see it as much.
Personally I'd rather have a gauge that tells the truth.

 

I agree 100%... Mine will bounce around all day until i hook to about 15k Then it sticks right at 185-190*.

 

After replacing the engine in my daughter's Honda, my mechanic friend emphasized watching the temperature gauge for ANY fluctuation. The Honda gauge NEVER moves regardless of ambient temperature or engine load. Around here we "test" our vehicles on a hill called "3 MILE HILL", a 9% grade that will heat up any vehicle.
The Honda despite being flogged up the hill, the gauge never moved.
I told the friend I NEED a thermostat in my Dodge Cummins as steady as that. He replied Honda makes their own thermostats and the design is unavailable in the aftermarket. He suggested trying a Robertshaw design.

The quest for a stable thermostat was on.
Purchased and tried about a dozen thermostats (eBay made that easy and economically feasible).
The Robertshaw design was problematic because of the disk needed to seal the bypass ports once the thermostat opens. Impossible to find with the sealing disk.

The "most stable" thermostat turned out to be a Motorad "426-190", all stainless steel with jiggle pins and integral "O" ring gasket like the original Caltherm 3937171 but of slightly lighter construction.
The Chinese appearing box said "Made in Israel", but the thermostat itself was stamped Germany.

The gauge needle isn't rock solid, varying about 10 degrees which is GREAT compared to the 50 degree swings for most thermostats in the Dodge Cummins.
The fluctuations now occur after backing off at the top of a grade, Lary Ellis is correct, the thermostat gets dosed with a slug of cool water, being an analog device the thermostat is unable to respond fast enough. The Motorad "426-190" seems to handle this faster and with less fluctuation than any other I've tried.
Best $20.00 ever spent on a vehicle part.

I hated those wide fluctuations so bad that I was considering designing a digitally controlled stepper motor valve.
Now that the installed 190 degree Motorad is functioning so well, I can live with the small deviations. It's a pleasure to check the gauges and see the temperature is right where it ought to be.
Cold weather is here again and the lack of large fluctuations has the added benefit of stable in cab heat, no more fiddling with the heat control every time the load on the engine changes.

 

Cummins "fixed" the temp swings to get rid of complaints, not what they felt was a problem in 1998 by moving the sensor and altering the electronics.
I agree with Cummins, the fluctuations are a non-problem that people waste too much time trying to correct.
What contributes to this perceived problem is people not using their trucks as they were designed for, loading up and working, not driving around empty all the time.

 

The original t-stat in my 12v, I would have a 20 degree temp swing on the mechanical gauge, from 170-190 constantly. I never noticed any change in heat output from the heater. I don't know what the gauges read in the 94-97 trucks, but my dash gauge is always steady on the low end of the scale, which is why I am guessing they installed the mech. water temp gauge to begin with. The orignal t-stat failed a year and a bit ago, put in a Cummins replacement, and it is steady as a rock at the 180-185 range, depending on ambient temp. It fluctuates once, when it opens for the first time. After that, it doesn't change.

 

Great solution to a "perceived" problem, definitely a novel concept.

Went out today a loaded 4 ton of gravel on the truck and 10 ton on the trailer, think that will be enough load to keep the temp gauge steady?
Oh, what should be done on the down grade to keep the load on the engine?

50 degree fluctuations hardly qualify as "perception". More likely a design flaw.

Wonder how many of those "53" block crackings were acerbated by 200+ degree water being too quickly cooled by a slug of cold water because the thermostat failed to efficiently moderate the water temperature.

 

My temps have been fluctuating for over half a million miles with zero engine problems, if the fluctuations are a problem they sure are taking their time.

 

A simple inexpensive Motorad "426-190" thermostat SOLVED my wide 50 degree temperature fluctuations.

It is inconceivable anyone could find fault (and further flippantly state it's nothing but a perceived problem) with a solution that ACTUALLY solves a long standing problem.
These persistent 'know it all' attacks certainly discourages folks from even posting anything on the internet(no I'm not thin skinned, just tired of these type posters). That is one reason there is actually less information on the internet now than there was 10 years ago, people are sick of the argument for argument's sake situation.

Slugs of ice cold water (in winter) passing through the engine block subsequent to the heat built up by ascending a grade can't possibly a situation anyone could logically accept, despite Cummins' self-serving statement that fluctuations are all so quite normal.

I have observed the coolant temperature after pulling a grade fall by 60 degrees within a few seconds, can't be a good thing by any stretch of the imagination.

 

You know, I have to ask for a source of that statistic.