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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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I have a ISL 8.9L 400HP Cummins in a 2008 Forest River Charleston. The Diesel has a rear mounted radiator. I pull a 18' V nose enclosed trailer with auto in it and I started having overheating problems from Flagstaff to Amarillo . I had the water pump and thermostat changed and it was good until I left Texas in December heading to Florida. I had a mechanic to come over to the RV Park here in Port Charlotte FL and he said the Fan Clutch was bad and the Fan just freewheels  and does not engage. His cost (plus 20% mu) is $1200. Is this a reasonable price? 

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On 3/31/2013 at 12:46 PM, wolfe10 said:

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.

Where is the engine serial number located? 

 

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14 minutes ago, qoajim said:

Where is the engine serial number located? 

 

Top side of the gear housing. Look just above where you add oil.

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I had some overheating on my 05 Mandalay  model 40E 400 ISL side draft radiator also and the Cummins dealer discovered that it had a bad ECM ( electronic control module ) which was not telling the hyd pump fan to speed up when needed for extra cooling, they installed a new ECM module and it had to be flashed, it does cool much better now but yes they didn't put a large enough radiator in it so I just downshift to keep the RPMS up for a better flow.  

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30 minutes ago, sunlover19 said:

but yes they didn't put a large enough radiator in it so I just downshift to keep the RPMS up for a better flow.  

Part is you don't drive a big rig like your car. You have to learn to drive it based on conditions.

Bill

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Thats so true, most times we have our toad behind us and drop down to 35 to 45 mph depending on incline and  conditions, can't drive it like my Corvette  !!! 

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Yup, a need for  a whole new concept on driving.  Putting it in "D" , hit cruise control and going is not a good one.  One has to (or at least really should) monitor conditions, coolant temperatures, speed on descents, etc.

In other words as the driver of any heavy vehicle, you must be alert!

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As a former twin engine motoryacht owner there are alot more gauges, vessel traffic, weather and tide conditions etc. to watch out for and your quote makes it sound like I'm not  "alert" at operating a motor coach 

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sunlover19,

No reflection on you personally at all.  We have no idea if you are brand new to diesel pushers or an old hand with a quarter million miles.

As with most threads, there will be people reading this in the future who span the whole range of experiences-- and posts are directed to that same wide range.

BTW, Dianne and I have about 25,000 sailboat miles-- mostly between Galveston Bay and the Bahamas. Indeed a different and more complex set of "how too's".

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IMHO, unless your in heavy water traffic or Blue water racing, there is no comparison to driving a big DP coach...in a coach you have to be on your game all the time.  There are too many variables coming at you and around you, to slack off, is an invitation to disaster! :P

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