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Overheating on Cummins 400 ISL

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We too have experienced intermittent overheating with our Cummins 400 in a 2008 Winnebago Ellipse (rear radiator). On three occasions (June, Aug, & Sep) the engine coolant temperature quickly rose from normal (179-189) to 230. Increasing engine speed made no difference, and in all three incidents we had to pull over and shut down the engine.

Once we restarted the engine (the last time within 2-3 minutes of shutting it down) the coolant temperature immediately returned to the normal range, after which it operated normally. The latest incident, just two days ago, the ambient temperature was in the fifties and we were on a relatively level stretch of interstate traveling at 55 mph. With the exception of these three incidents, the engine coolant temperature falls in the 179-189 range except for very hot days and/or significant grades (when it may go to 205 or so).

We spoke with Freightliner Customer Service and the tech suggested a faulty fan clutch. Does this seem possible? Many thanks to all for your insights.

First thing is determine IF you you have a fan clutch. Access the fan from below or from above (bedroom). With engine off and cold, grab the a fan blade and try to turn it. If you can't, you have a direct drive fan (no clutch). If it turns relatively easily, you have a fan clutch.

And if overheating, the best thing to do is to pull over in a safe place, place the transmission in neutral and raise the RPM to 1500 or so. Do NOT shut the engine down hot unless the above procedure produces even higher engine temperatures.

Note: Thermostats DO stick and could give your symptoms-- work fine most of the time, but "hang up" once in a while. They are inexpensive and easy to replace. I would do that as preventive maintenance.

Lastly, with a rear radiator, you need to check for blockage of the after-cooler (what you see when you look inside the fan shroud/between fan blades-- easiest from ABOVE (bedroom or closet depending on layout). With a strong flashlight, verify that the perimeter is as clean as the center (the fan blades "sling" the dirt to the perimeter). This will not cause intermittent overheating, but will reduce effective area of the cooling system, so it is more prone to overheating under heavy throttle conditions.

Brett Wolfe

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I have a 2007 Mandalay 40F with a 400 ISL, with a side radiator.

My temps run from 195-197 up to 205, which I thought where a little high! I have a friend who has a 2007 ALFA with the same chassis and drive train and his runs between 178-185!

So I took mine to Freightliner in Tollison AZ to have it serviced. When I told Kirk that mine was running 195-197 range, he said that’s what it
should be running! When I told him about my friends couch running at 178-185 he said that was to cool! So what’s the real deal?


Rick DeWitt

2007 Mandalay 40F

Sierra Vista AZ


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Rick,

Welcome to the FMCA Forum.

Rather than get opinions, tomorrow give Cummins a call with your engine serial number. THAT is the source of FACTS on your engine: Cummins 800 343-7357.

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We had a similar problem in our 2004 Monaco Dynasty with the 400ISL. It turned out that the radiator fan has a hydraulically operated variable speed motor on it. It was going bad. But, on top of that, the hydraulic system was driven by a similar variable speed motor. This was not the slide out hydraulics, it's a separate system from the slides.  The slide pump is a small pump that is mounted with the tank under the door and behind the steps. That went bad a few years back and I bought a replacement pump from the manufacturer  for $90. Monaco wanted $900 for the whole assembly, when all that I needed was the pump.

Back to the radiator. The way that we discovered it was that the fan would not come on till it reached a higher rpm (in the shop) and then it would stop under a load after running for a while, causing the overheating. 

Problem: both pumps are Italian made, available only in Italy, and not handled by any American manufacture. Someone put me in touch with a Country Coach dealer, in Portland, Oregon, now retired, who knew all about these pumps because Country Coach uses them also. He ordered them for me from Italy and in a matter of a few weeks we were back on the road. They cost about $1900 each delivered to my door. OUCH!!!  ON the other side of things, we just returned to Houston from Colorado Springs, and I noticed that going through Raton Pass that my temp gauge got up to 200 when it usually rests around 180. So, it could be this very hot weather that we're having. Good luck and hope this helps. 

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Max of 200 degrees F is just fine for your ISL. 

You DO want a temperature delta between "thermostat wide open" and fan speed spooling to max.

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