Went on a trip 2 weeks ago towing travel trailer , and had some overheating 2nd day.
Had thermostat changed in Ga. Ran OK for a week then overheated on 1st. day of return trip.
Got to a dealer in Fl. who diagnosed bad radiator , so after many bucks left with new rad. , hoses and serpentine belt.
Within 100 miles overheated again. Got to another dealer in South Carolina , who diagnosed variable fan not working and belt tensioner not up to spec ,so after many bucks left again.
Went 35 miles and overheated once again. Limped home by filling radiator every 50 - 100 miles.
Dealers pressure tested system and said no leaks. Fluid seems to be blowing out the water bottle. At the last overheat in S.C. as usual the radiator was cool to the touch until I let the steam out and some fluid boiled out then it was too hot to touch. Also when it's getting ready to get hot no heat comes out of the heater in cab.
I'm wandering if the thermostat is bad? What else could it be?
Sorry for long post ,wanted most details posted. Thanks.

 

I hate to say it, but first of all, you had several "bad diagnoses" in a row. Maybe you should pursue some recourse for repairs that didn't help. Having problems on a trip isn't fun at all.

Secondly, when you say fluid is blowing out the water bottle, are you seeing bubbling, such as air coming though the line? I really don't like to mention this, but it's probably your head gasket. With as many times as the engine has been overheated and cooled (thermal cycling) it's also quite possible that you have a warped/cracked head by now, as well.

Unless it's a rare type of failure or oddly designed thermostat, when a thermostat fails, it's designed to default to "open" and you get a very low indication on the temperature gauge. Fairly standard practice, likely not your problem now. Good luck with all this...

 

When I first got my truck it to would overheat. I changed the $7.00 napa thermostat out with the Cummins stat that costs 4x the amount.

Truck hasnt overheated since.

 

I agree and disagree with 96_12

You had a string of bad diagnoses on your trip, amazing what some people can do to get some "quick easy bucks".

On the opposite, thermostats DO get stuck don't open and let your motor overheat.

I don't know if you have any mechanical knowledge, but if this happens again try to get some wrenches and remove the tstat, motor will run cold but will save from damaging the motor completely.

I would get a reputable and known (to you) shop to do a pressure test and leakdown check of your cooling system.

 

I'm thinking head or gasket. Mine had 5 cracks in the head through the valves and would use about a gallon of water every 500 miles. I did notice steam out of the puke tube while at idle but it was not really apparent. Some head gasket, or cracked head issues won't show up until the motor is hot and they open up. Cheap fix do another thermostat and see if it helps, but I think you will need to pull the head to find the culprit. Good luck.

 

The engine did not run long when hot . I have been told from a couple of guys that it could be head gasket. How big a job to fix? I may first try thermostat. Thanks for responses.

 

Forgot to answer 98 12v , yes I did see bubbling in the water bottle when it was hot. At idle at both dealerships it ran for quite a while and fluid seemed to be cycling normally. Running on the Interstates it mostly was OK until I slowed in traffic on pulled off.

 

If you pull the head make sure you check it very carefully for cracks and warpage, also the block to make sure it's true. Trust me check for the cracks carefully, it sucks having to do it twice.

 

It seem obvious to me that no water was circulating from the engine through the radiator. You had a new thermostat so unless it failed closed what else is in the circulation loop?. Did anyone look at the water pump? No circulation.

 

The first Dealer told me they never saw a water pump go bad on a cummins in 30 yrs. so they felt it was the radiator since it was showing uneven temps across it when checking with a digital temp sensor.