fluctuating temp gauge

[mazdarotary]

Hey guys,



Long time no write. On my way to work tonight I noticed the temp gauge on the ole diesel was not sitting at it's normal operating piont. It usually sits at the second mark on the gauge and does not move from there ever. Well tonight it was fluctuating from between the first and second mark to just past the second mark. It has never done this before to me. I am thinking thermostat,but it was replaced back in June when I did the radiator replacement. I used a brand new Cummins thermostat,and the fancy blue coolant when I did it.



What do you guys think?Thermostat?Water pump?Other?Any help is appreciated. Thanks

 

[WashingtonFLHTRider]

You have my vote for T-stat.

 

[cerberusiam]

Ummm, the fluctuation seems to be the operational norm. I would get worried if it quit bouncing around.



Maybe the gauge or sender had a problem before?



I know, I am absolutely no help, but I try.

 

[don b]

my guage fluctuates too. i think it is caused by the thermostat opening. it goes to the second line and then drops quickly. also my clutch fan goes on for short intervals before the engine reaches normal operating temperature is this normal?

 

[bgilbert]

What Cummins t-stat did ya get? What pn? Updated one? Some are know for fluctuating. Mine doesn't at all. I must of got the good one. Even with a mechanical temp gauge, it holds 165-170*, depending on outside temps. Of course, I'm thinking that temp is a little low, but maybe my clutch is locked up, lower temp t-stat, don't know, hey Sam, what does your mech temp gauge run at??

 

[Greenleaf]

When I installed the "new" thermostat the temp gauge dosn't stop moving.



-S

 

[mazdarotary]

I belive it was the updated version t-stat I used. Ir emember there being a gasket looking thing with it that was blue and said "this is not a gasket"on it. I read the directions and it was a stencil for grinding out the housing so that you could use the updated t-stat. I didn't have to do any grinding,so I think I have the updated t-stat. WHat do you guys think?

 

[JLEONARD]

Mine doesn't move either once it's up to temp.

Jay

 

[Greenleaf]

I have no idea.

I installed the same thermo in my truck as in the school bus engines. The bus engines do not constantly change temperatures like my truck does. I have never seen any instructions included with the new thermo. I have seen that blue thing that is not a gasket and thrown it over my soulder cause I have no idea what it's for.



I have always bought a Cummins thermo part # 3802968



Scott

 

[Grey Wolf]

There is a part number for one that doesn't fluctuate, but you'll have to do a search to find it. However the service manual does state that the fluctuation is normal and has an illustration of exactly what your describing. By the way mine will do that also, unless I put a load on it or if the outside temps are hot, then it holds steady... .....

 

[tugboatphil]

I don't know if it is the IC, but my 90 never moved at all, once it was up to temp. My 93 will fluctuate, but not always. I guess it depends on the outside temp.

 

[TKingsbury]

Mine also runs rock steady. The only time it didn't was when I refilled the cooling system on the road after a leak, it moved around like mad for 5 or 10 miles until all of the air was out of the system. I vote for your gauge or its circuit has a problem.

Travis. .

 

[mazdarotary]

I will admit I don't always pay close attention to the temp guage(mainly because it has always been rock solid before),but it has been cooler the past few weeks here in New England. I don't drive the truck all that much anymore,so maybe it has been doing it since the weather has cooled,and I hadn't noticed it yet. I will keep an eye on it for the next week or so and see if it keeps doing it. Maybe I have some air in the system as well. I still think it is the thermostat but I don't understand why because I used a brand new cummins t-stat in June. Thanks for the input guys.