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jtaylor0521's avatar
jtaylor0521
Explorer
Jul 30, 2013

Diesel engine running hot at 58 mph in the mountains

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.
Class A
  • Terryallan's avatar
    Terryallan
    Explorer II
    Jul 30, 2013
    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's avatar
    the_bear_II
    Explorer
    Jul 30, 2013
    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.

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