I am new to the forum, but wanted to pass on what I consider a close call. In early February, I was travelling through eastern Oregon, toward Nevada. Outside temps were in the mid-30s and I had the cabin heat turned on. All of a sudden, the cabin got cold and the temp gauge spiked toward the maximum then dropped to the left peg. I pulled over ASAP and found that the hoses were slack, no coolant, but coolant was blown all over the right front undercarriage and splash pans. I got towed in to Bend. Oregon and the Dodge dealership told me I had a thermostat that had stuck CLOSED. I could have burned up the engine, cracked a head, or scored the cylinders, all potentially very expensive. The rig had 46000 on it at the time, and that part should have been under warranty. Guess what? It isn't. Diamler-Chrysler and Cummins really weasled on that one part that could potentially lunch an engine.

Just a warning to the group. Keep an eye on your temp gauge. The dealer installed thermostat makes the temp gauge cycle between 140 and 180 constantly when driving on the highway.

Has anyone else had a similar experince?

Thanks

 

Haulin in dixie has. Ate two engines because of it. I keep a close eye on mine. It stays right at 190 or a needle width above it. Which I hate because it kicks the hurricane on.

 

This is one advantage to having a late-build 02. Mine already has the correct thermostat, and yes, it DOES constantly cycle from 140 to 180.

The reason the for the cooling system cycling is that the cooling system has a large cooling reserve. Also, the thermostat has different opening and closing temps. It might open at 190, but close at 140.

Let's go through an example. When the engine's cold, the t-stat is closed and temp comes up. When engine temp hits the opening point of the t-stat, it opens, and the hotter engine coolant mixes with the colder coolant in the radiator. Thus, an instant drop in overall temp.

However, because the cooling capacity of the radiator is so large, the coolant will cool off faster than the engine heats it (assuming steady hwy cruise, empty). Thus, overall temp drops until the t-stat closes (140ish or so). With it closed, temp comes back up and the whole process repeats itself.

If they made it so the thermostat opened and closed at the same temperature, you'd have a LOT of thermostat cycling and premature failure.

BTW-- Robert Shaw Thermostats are pretty good.

Justin

 

I just changed mine. It stays @ 190 +/- a needles width.

 

What part number is the new one? Should I expect to get it if I got to Cummins and say "gimme a thermostat"? Thanks!

Matt

 

Sounds like you have the same thermostat as me. A needle's width below 190 degF running empty - a needle's width above 190 degF when towing our 36' 5th wheel (21,180 lbs GCW versus 21,500 lbs GCWR).

Rusty

 

Thats it rusty. Same as me, and Im satisfied with those numbers.

gsdog:

THe guy at Cummins told me that the thermostat # had been changed allot. Do a search on thermostats, and you will find the correct part numbers. I posted them awhile back, but I cant remember where! I just changed mine out 2 weeks ago.

 

There are many recommendations of Bars Leaks in any engine and the stuff will not hurt the engine, this is true. With the crack on the last block, I ran a few thousand miles and used a bit of Bars Leaks in it. When I tore it down I discovered a surprise. The thermostat received a buildup on top of it that could easily trash the performance of the thermostat. This surprised me because it is stock OEM material in many engines, like motorcycles, some cars, etc. Never saw the buildup on other vehicles. It did not plug the heater or put a buildup on the engine surfaces. Before shutting the truck down for the new engine I had noticed some funky thermostat action, which was obviously the thermostat starting to stick.

 

Bar's leaks is a no no! I made the mistake of using that once in a ford... plugged the radiator, heater core, thermostat, and cracked the head!

 

Mr. Hohn:

Thanks for the explanation for the cycling of the temp gauge/thermostat. That makes sense and shows that the deep cycling is actually a good thing. See I learned something with my first post. Thanks to all of you.

DrDip

 

I don't know why 40 degree cycling would be desired. Most motors like some heat in them...particularly diesels.

An old racers saying is "it ran best just before it blew up due to heat". An old diesel (train) saying "the hotter she runs the faster she goes the hotter she runs the faster she goes, the hotter..........

 

GREAT!!! I wish the correct info would get out sooner. I was a day away from getting some Bars leak because I have read MANY post's saying "get Bars leak because it will stop cavitation and is good for the system". Now its no good??? Whats the deal?

 

I only related what I found when tearing down the engine. I used a lot of it. I doubt that it would help cavatation though. Might treat the problem but not the cause.

 

my 97-12valve fluctuated 40degrees the whole time I had it. I never changed the thermo, or the coolant.

my 01-24valve fluctuates a needles width over and under 190. I like this better.

 

The 40° fluctuation isn't necessarily a good thing. But it's better than the alternatives: constant thermostat cycling or overheating when working the engine hard.

And yes, it's true that the hotter the engine runs, the better-- right up to almost the point of melting. At least for the combustion process and cylinders-- for the cooling system and such, it might not be so good.


If you could see a graph of cylinder bore wear vs. operating temp, you would be quite surprised. The hotter the operating temp of the bore, the LOWER the cylinder wear. This has been proven time and time again.

Ever wonder why the guys who constantly tow seem to get a LOT of miles out of their engines?? Think about average EGT.

It's not intuitive, but the closer you can get to 1150 EGT without going over (sustained), the longer the engine will last! You CAN have too much air.

Think of it this way: the OEM Dodge spec limits turbo boost to 20-21 PSI. But a stock ETH will also hit 1300 EGT pretty easily. Dodge COULD have easily let the turbo run up to 25-26 psi and dropped EGT down into the 1100 degree range. But they didn't!!! Ever wonder why?

Maybe to LOW an EGT is just as bad as too high?? Why do they tell you not to idle your CTD for long periods-- right EGT gets too low!!

Something to think about anyway.

Justin