What Thermostat?

[Greenleaf]

Hi Guys,

I installed a new thermostat and the engine's temp guage is indicating a hotter reading. The needle has moved a bit farther than the norm.



I installed a Cummins #3802968. Is this the right one? Are there others? I called the dealer and this is the only unit listed for the "B" engine.

The original was removed because it was original with 180+ thousand miles and I had the coolant out anyhow.



What do you all think?



-S

 

[Greenleaf]

I think I answered my own question. I just called another Cummins dealer. The 3802968 is the only unit listed. Apparently, you can't get a various range of thermostats for our diesels like they can for the gassers.

-S

 

[bgilbert]

Wrong! There are quite a few 12V Cummins t-stats. Run a search, you can get various part numbers. Yeah sure, I guess the dealer might have been on the right path aobut one can't get a various RANGE= temp range I assume= but we have various 12V t-stats. Only thing is some of them will make the factory gauge run different. Whether or not our temps are running colder or hotter, well no true temp gauge here so I don't know. Some will make the temp fluctuate. I guess some have different tolerances. Sure I imagine there all suppose to open at said temp say 181* and fully open at say 210 give or take but according to the fellow TDR members that have posted in the archives, they all run different. I changed mine a ways back can't remember the PN but its supposed to be the updated stat that doesnt allow temp fluctuation, don't think its the PN you used. After changing it, my fact gauge ran LOWER. Used to run on the second mark, then after new gauge ran on the FIRST mark. I ended up changing the gauge with my gauge clusters parts bin. With different gauge temp now reads at normal operating temp at the 3rd mark, enough for me. I hope this makes sense and helps someone.

 

[Greenleaf]

Its tough to say what the temp really is fo' sure.

I only have the factory guage. It used to always stop just short of the second hash mark. The first mark being the one on the far left,that begins the normal operating range.



The guage will now travel over to the second line, indicating it's operating hotter. I don't think it will be a problem, but it's a concern as I'll be driving to Hot-Humid-Sunny-Florida soon and pulling a trailer on home.



-S

 

[dpuckett]

Mine have always run around the second mark in the "NORMAL" range; some above, some below. As long as you stay below the 3rd mark, you should be ok. My current one runs about 2-3 needle widths above the 2nd mark. Sometimes pulling hard, it will get to dead center before sweeping back to between the 1st and 2nd mark. Not often enough for me to waorry with changing it, though.



Daniel

 

[Greenleaf]

Now I know what you guys "R" talking about. Took the Dodge for a nice long drive... . under a steady throttle the temp guage sweeps back and forth like the old clock @ the house. While setting @ a stop light, it holds steady. I don't think there will be a problem with it out on the open road pulling a trailer. I don't understand why this is different from my old thermo. I use this same unit in the bus engines and it doesn't sweep the needle.



-S

 

[BChamberlin]

Mine also swept back and forth after replacing the h2o pump. It stopped after I was able to get all the air pockets out of the system.



BC



'93 w350

 

[JLEONARD]

under a steady throttle the temp guage sweeps back and forth like the old clock @ the house.

Maybe this won't hurt the engine, but the thermal cycling can't be doing any good.

The needle should be stable... climb a bit while you're "putting the wood to her" and fall as you decend on a grade or come to an idle.



In the marine application an air pocket could easily be a big problem... been known to take out head gaskets in a single bound.

A marine ngine is always under a load and you don't want a hot spot... the air pocket will be in the head. . # 6 or # 1 depending on which way the engine is facing in the boat.



Not as big a deal in a truck engine. . but I wouldn't want to take that risk.



The needle on my temp gage doesn't vary more than the needle width once it comes up to temp... of course I have the old style radiator. . the one that is supossedly no good



Jay

 

[Greenleaf]

I learned to fill the system slowly and allow it time to purge the air. The bus radiators will have a caution sticker to warn of entrapped air if filled too rapidly. Some have a bleeder screw located at points throughout the system.



-S

 

[JLEONARD]

Some have a bleeder screw located at points throughout the system

Yes. . the marine engines have vent hoses that lead into the top of the expansion tank... I had to add some because I had a nose down installation. . one top rear of the head, one on top of the turbo (turbo is antifreeze cooled and mounted on top of the exhaust manifold).



My son puts a vaccum on every system he refills and draws the antifreeze in that way... never gets an air bubble that way!