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Old 06-30-2009, 05:07 PM   #1
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400 Cat overheating problem

I have a 400 hp cat engine in my 05 motor home. I am having an intermittent overheating problem.
The first time I had it in Kingman Az. 3 months ago. The cat dealer said the t-stat was sticking and replaced both of them. Last week it overheated again (237degrees) I pulled into a flying j and waited 20 min. and took off and it worked fine. Temp would go to 194 then t-stat would open and temp would drop to 183 and start cycle over again. Then on return trip the same thing. It is now at the cat dealer in Indianapolis and they tell me there is no problem, even though the computer shows it has overheated. They canít make it over heat on the dino. I told them It doesnít always over heat. He said it could have been the weather (outside temp). I donít buy it the temp was the same when I left flying j as when I pulled in.
Does anyone have any idea what the problem could be.
By the way the fan is working ok. And I also had the radiator steamed cleaned, and coolant tested

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Old 06-30-2009, 06:04 PM   #2
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I can't help ya, but I can say howdy and welcome to iRV2. MY first thought was thermostat or fan, both of which you already tried. My other thought is a blockage in the water flow somewhere but I have no idea how to test that. I am sure someone will be along soon with some ideas. We have some pretty good mechanics hanging around here.

We do hope you continue to visit with us and share your experiences. Be sure to let us know what the final resolution is.

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Old 06-30-2009, 06:09 PM   #3
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If you have a 190 degree thermostat then the 187 to 194 would be normal. Those thermostats are only accurate to within 15 or 20 degrees at best. Almost every motor uses a 190 thermostat anymore for pollution control.
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Old 07-08-2009, 06:43 AM   #4
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Thumbs up Overheating Cat.....


Do you have "shutters" in front of your radiator?

If you do they are pneumatically operated, check the air line for possible leaks and the connections for tightness. A small leak here will close the shutters and cause an overheating situation. Also check the linkage operating the individual vanes.

I hope this helps,

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Old 07-08-2009, 08:00 AM   #5
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Since you replaced your thermostat, it would be good to look at your radiator fan control. There have been reports of the controls on the fan being controlled poorly although an intermittent problem has not been discussed. A check you can make is to open a window and listen for the fan when you get the overheating problem. The fan should be at maximum speed and be loud.
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Old 07-08-2009, 08:30 AM   #6
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If it is a rear facing radiator you probably have build up on it. Its a common problem with the cat. The breather tube blows oil residue on the radiator and then collects dirt and causes air restriction. Some degreaser and a hose should solve the problem. They should be cleaned at least once a year
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Old 07-08-2009, 06:51 PM   #7
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Zman he already steam cleaned the rad.
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Old 07-09-2009, 07:57 AM   #8
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Originally Posted by J Walker View Post
Since you replaced your thermostat, it would be good to look at your radiator fan control. There have been reports of the controls on the fan being controlled poorly although an intermittent problem has not been discussed. A check you can make is to open a window and listen for the fan when you get the overheating problem. The fan should be at maximum speed and be loud.
You may be on to something. The fan is running but I am not sure if at full speed. I had the t-stats replaced again, then left Indy Tuesday AM. went about 150 miles with temp never over 185 then all 0f a sudden it went to 210. I stopped for 30 min. and then it went back down and ran cool again. The other thing I have noticed is the trans. temp comes up with the rad. temp. I will try to check the fan rpm
thanks for your help,
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Old 07-10-2009, 07:32 AM   #9
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If overheating it should produce steam just like an automobile. If no steam, maybe it is not really overheating and the gauge and or computer sensor are providing false info.
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Old 07-10-2009, 07:43 AM   #10
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My parents had a overheating problem on their last pusher with a Cat. They had to get the radiator power washed. I think it involved taking it all the way out and power washing it off the coach. They went thru all the other causes just as you are doing here too. Just a thought....But if I recall their over-heating started when there was a little extra load being applied such as a small mountain pass or a small uphill grade.

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