Diesel engine running hot at 58 mph in the mountains

[jtaylor0521]

I have a 2005 Monaco Cayman 37' with a 300 hp cummings engine. Yesterday was the first time we have encountered mountains. I was running in 5th gear at 58 mph up and down the hills on I40. I noticed it was runing hot, over 200 degrees for awhile the it really started to heat up until the check engine light came on. I stopped and checked everything and it all checked out and the engine cooled down, so we started out again, watching the temp gauge. When it started to heat up again I down shifted to 4th and ran at 53 mph. The engine cooled of to 200 and I had no more temp issues.
My question is: How fast can I run in 4th without causing problems. The RPMs are 2200 at 53 mph in 4th gear.
Is it normal to run hot in the mountains. BTW the outside temp was 85 degrees.

[ScottG]

Dump that Chinese made "Cummings" knock-off and get a true CUMMINS!

[hershey]

If its a rear radiator Golden HVAC is on the right track. Cummin's has a slobber tube at the top of the engine. It will let a mist of oil, over time, blow directly into the radiator. That with dust and road grime will slowly plug the radiator to the point your at right now.
Find a large do-it-yourself car wash and back up to the bay if you won't fit and spray liberally with a strong solution of Dawn and/or Simple Green or Awsome. Let it sit and spray it squarely with just plane water from the rear. That will flush the bad stuff back to where it came from. Thats the on the road solution to your problem.
Once your home, continue to saturate with de-greaser and wash from the rear and also from the front. There is a turbo aftercooler there too and unfortunately a lot of the bad stuff will stay caught between the radiator and the aftercooler. Just perseverance can get much more of the radiator clean.
Once you feel good about it, connect a rubber hose to the slobber tube and route that mist down and below the radiator so you don't have the problem again.
My MH was so bad I had to have the radiator pulled and washed and the aftercooler also and replaced.

[JimM68]

does your cayman have the "standard" midprice monaco layout, ISC engine, rear radiator, charge cooler above the radiator, not sandwiched with it, and engine driven mechanical fan?

That is how our 08 knight is layed out. Our engine temp never varies, sits at 180 always. Double check your guage through the alladin system, but if you got a check engine, it was hot, and that's not normal.

For sure clean the radiator as stated above. I do mine once a year. Without the charge cooler sandwich, the cleaning is pretty easy.

RPM and gear should not be something to even think about. Mr. Allison and Mr. Cummins will put the gear and rpm where they need to be. These systems won't let you lug the engine. I try to keep my foot off the floor going up hill, past a certain point all it does is waste fuel.

[Golden_HVAC]

Hi,

Try spraying on some simple green water mixture on the radiator, and let it soak. Rinse with a generous amount of water from the garden hose. You should get out a lot of dirt, and that might solve the problem for another year or so.

Some municipal busses get washed every 3 months, and have a ton of dirt on them from the intercity streets.

Home Depot has a 2 quart chemical sprayer, it works great to get the soap mixture deep into the radiator. Use about 60 - 75% water, and simple green.

[JumboJet]

Cummins engines can run at red line all day long. Not that I would do that.

[1492]

Moved from Forum Technical Support

[Terryallan]

The higher RPM does 2 good things. It circulates the coolant more, Cooling the engine, and transmission.
Somewhere in your manual. there should be a section telling you what your Minimum RPM should be. In the big truck. Our minimum was 1500. We never ran it under that. Lugging is NEVER good for the engine. Can cause it to use oil, and will waste fuel

[the_bear_II]

The one thing you don't want to do when climbing a grade is to let the engine lug. Downshift and maintain the RPMs at an acceptable level and you will be able to climb grades all day.

That being said you need to make sure your temp guage is accurate. The guage on my truck showed a temperature that was 20 degrees higher than the actual temperature measured by a certified accurate aftermarket guage. So when I thought I was hitting 220 I was only at 200.

Also if equipped with a fan clutch make sure the fan clutch is engaging.