My barth has a 235hp 1996 5.9 cummins that starts overheating after about an hour of driving at 65 mph. The exhaust temp starts climbing to 12 and have to slow to 55mph to run the exhaust temp back down to 9 or 10 also brings water temp down on temp gauge. I've been told that running down the road with exhaust temps over 12 will start causing major engine problems. Is this true ? Also how much of a factor is this new low sulphur fuel affect engine temps ? I removed the radiator and heat exchanger and had them cleaned out and pressure checked. Also installed new belt and adjusted valves. Still same. Any thoughts from anyone ? Could it possibly be the fuel pump needs tuned ? I also installed a oil temp gauge thinking the water temp sensor could be it but both gauges show high temps. I also checked the antifreeze with a gauge and its a good 50/50 mix. I've read this alot with the 5.9 235 HP engines and is this a typical problem for these 5.9"s ?

You didn't mention what the water temp got to?? I have a 94 230 HP Cummins and do not have an exhaust gage (will have later)so I can not give you a comparison, I also have a 6 speed which keeps the RPM quite a bit lower. When I go to areas in Nevada (in May) outside temps were 100+ and the engine temps would go to 210 up a grade, and on the flat and level at 70 MPH I will run 180 but if the outdie temp goes above 90 or I am in higher elavations, it will go to 190. I had to down shift manually on the grades to get the engine RPM up so that I had better fan speed which would help.

I changed the muffler because the input pipe broke off and it was pouring exhaust gases into the engine area which would cause the temps to rise very fast, I also installed a second heat shield so that the muffler heat is directed out the back.

On this trip I haven't seen any coolant temperatures over 200, but it has been much cooler and lots of rain.

One other thing that I forgot to mention, make sure that your air cleaner is clean and the intake is not kinked! Reduced airflow will also cause overheating or increase operating temperatures.

Let us know what you find.

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make sure that your air cleaner is clean and the intake is not kinked!

Is there a Filter Minder? In addition to troubleshooting, they can pay for themselves in filter costs, especially with diesels.

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Originally posted by MWrench:
...make sure that your air cleaner is clean and the intake is not kinked!

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Originally posted by bill h:
Is there a Filter Minder? In addition to troubleshooting, they can pay for themselves in filter costs, especially with diesels.

Good advice...

I worked on one coach with a slightly applied exhaust brake. He had it to 5 different shops in as many state. He never figured out that it only happened after he used the exhaust brake because the overheating would happen about 15-20 miles later.

After heading out on the service call I noticed his exhaust brake was partially applied. After tapping on the shaft and lubricating the linkage it worked great. He was hesitant to pay me too for fear that it wouldn't work.

I got a call from him after he ran thru 4 more states in 2 days without another problem. He couldn't believe that a road service tech figured it out before a dealership did.

He reported more power, a better exhaust brake and more cooling even while going into hotter southern climates.

Also found another coach with a variable vane problem on his turbo. Wouldn't be the case with you but thought I would post the link anyway. Rv Service Center Review.