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.

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.

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

Moved from Forum Technical Support

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

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.

Diesel engine running hot at 58 mph in the mountains

ghostrider421
Explorer
Aug 04, 2013
CarlGeo wrote:
a real CUMMINS engine they seldom have over heating problems!

They do if the clutch fan isn't working.
Jarlaxle
Explorer II
Aug 04, 2013
2200 for a C-series is hardly lugging!
CarlGeo
Explorer
Jul 31, 2013
Those "CUMMINGS" engines are known to run hot, but if you can get a real CUMMINS engine they seldom have over heating problems!

Good Luck
rgatijnet1
Explorer III
Jul 31, 2013
DanTheRVMan wrote:
rgatijnet1 wrote:
The ONLY Simple Green product that can be safely used on aluminum surfaces is "Extreme Simple Green", which is specifically made NOT to cause corrosion on aluminum. I agree that your radiator needs to be cleaned, but use the right product and not something that can etch away at your aluminum fins if not thoroughly rinsed off completely. The standard Simple Green concentrate must not be left on any aluminum surface for more than 10 minutes and if not completely rinsed off, which is difficult to determine with a radiator, can accelerate corrosion.

good comment, but where do you buy it?

The Home Depot by my house sells it so it may be available at other Home Depot stores.
DanTheRVMan
Explorer
Jul 31, 2013
rgatijnet1 wrote:
The ONLY Simple Green product that can be safely used on aluminum surfaces is "Extreme Simple Green", which is specifically made NOT to cause corrosion on aluminum. I agree that your radiator needs to be cleaned, but use the right product and not something that can etch away at your aluminum fins if not thoroughly rinsed off completely. The standard Simple Green concentrate must not be left on any aluminum surface for more than 10 minutes and if not completely rinsed off, which is difficult to determine with a radiator, can accelerate corrosion.

good comment, but where do you buy it?
Canadian_Rainbi
Explorer
Jul 31, 2013
hershey wrote:
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.

DON'T use a carwash wand on the radiator unless it had a LOW PRESSURE setting. Full power from a pressure wand can damage the radiator fins!
JamesBr
Explorer
Jul 31, 2013
I concur with the cleaning of the radiator. But you may also be too aggressive int he summer heat climbing the hills. Even with a clean system (I can see a flashlight through all the way through the two sets of fins.) Summer time climbing grades I need to keep an eye on RPM, boost pressure and water temp. I can usually keep the temps around 200 give or take but sometimes I have to run at a slower climb then I thought I would.
rgatijnet1
Explorer III
Jul 31, 2013
The ONLY Simple Green product that can be safely used on aluminum surfaces is "Extreme Simple Green", which is specifically made NOT to cause corrosion on aluminum. I agree that your radiator needs to be cleaned, but use the right product and not something that can etch away at your aluminum fins if not thoroughly rinsed off completely. The standard Simple Green concentrate must not be left on any aluminum surface for more than 10 minutes and if not completely rinsed off, which is difficult to determine with a radiator, can accelerate corrosion.
jtaylor0521
Explorer
Jul 31, 2013
Thank you all for your great advise. I learned alot and will clean my radiator.
Jeff
JackMS
Explorer
Jul 31, 2013
All advice above is great. I will just add that the engines ECU will not let you over rev the engine, except maybe going down a hill.