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Old 07-25-2010, 03:11 PM   #1
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1992 Foretravel U300 Engine Overheating

This is the first summer season we have been able to use our coach and have discovered an engine overheating issue. 36ft coach, 30,000gvw, 350hp 6V92 detroit, allison 4spd, side mount radiator, hydraulic cooling fan. The radiator was rebuilt about 4,000 mi ago. Coolant level is o.k., Hyd fluid level o.k. and of the proper type, the radiator appears to have clean fins.

On a pull (anything over 2%) in 85+ deg weather the water temp would pass beyond 215deg if I allowed it. I shift down and in a matter of a minute or two the temp heads backup, shift down again and the same problem. When it decides to go up it does so quite rapidly.
When we get on a flat or down grade the temp almost instantly goes back down to it's normal 190-195 deg.

I don't know how the fan system is supposed to work and therefore I don't know how to troubleshoot the system. The fan is working and when I pull over the temp drops so fast that by the time I can get to the engine compartment and shoot the radiator with our IR thermometer, all appears normal.

How can I determine if the fan is working correctly under engine load or if the heating is another problem?

If anyone can describe for me how the hydraulic fan system is supposed to work I would appreciate it and then I might be able figure a plan of attack.

Thanks.
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Old 08-14-2010, 10:14 AM   #2
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The fan is controlled by a thermoswitch. It should keep the water temp around 180 to 190 always. Never exceed 215 for any length of time. I would check the fan thermoswitch (2 most likely) and the engine thermostats. 2 of these as well. The detroit is awesome engine but, DON'T over heat it. Good Luck
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Old 08-14-2010, 10:21 AM   #3
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Detroit engine 92 series where famous for cracking the heads on an over heat. keep close eye on it after you find the overheat problem.
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Old 08-14-2010, 11:55 AM   #4
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If you have a fan over ride switch, turn it on, or manually gear down on the big hills. keep the rpms up and all your fluids will be happy
I have a 6v92 in my coach and thats what I do.
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Old 08-15-2010, 09:02 AM   #5
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Quote:
Originally Posted by jholder View Post
The fan is controlled by a thermoswitch. It should keep the water temp around 180 to 190 always. Never exceed 215 for any length of time. I would check the fan thermoswitch (2 most likely) and the engine thermostats. 2 of these as well. The detroit is awesome engine but, DON'T over heat it. Good Luck

The hydraulic fan system on our coach is pure hydraulic. No electric anything. Maybe thats the problem.............
From the reservoir there are hoses to the pump, from there to the fan hyd motor and back to the reservoir. The only other item is what I think is a high pressure bypass valve that allows the oil to go around the fan motor.
The fan cannot go any faster than the pressure allowed by the bypass to go.
I don't think the bypass is supposed to be the controlling element but rather an emergency device.
What kind of fan motor is used for the electric speed controller and what does the electric device do?
I would really like to get our system fixed correctly. Today we will be traveling South in the Mojave desert, climbing 2500 ft in 100+ deg temps.
Somebody put a water sprayer on the radiator instead of fixing it right I am finding out. Today we will be using a lot of water.
Thanks for the help of all of you.
Gary
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Old 09-04-2010, 09:30 PM   #6
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Hi,
You have the exact same rig we do. Check the pump belt. It should have the same number of groves as the pulley on the engine and hyd. motor. The tensioner should be keeping it tight. With the engine up to temp., check to see if the fans are in the high RPM mode. A lot of owners are operating with an incorrect belt, too narrow or wrong length. The condition you describe is abnormal. A two percent grade should not take the gauge off the thermostat. The DDEC will shut the engine down before you crack a head or do other damage. That is why they put it there. The electronic controls take operator error out of the loop or at least most of them. Next step would to take it to a radiator shop where they can check temps across the radiator with an IR gun and check for products of combustion (leaking head gasket) in the coolant. A faulty thermostat that only opens part way could also be the problem. I do have to drop a gear or two in hot weather on a long grade. I don't let it get above 220 for any length of time. The 6V-92TA is a super engine and should run a million miles in the 350hp configuration. In some boat installations, it is set up to put out 550HP (along with lots of heat).

Best,

Pierce & Gaylie Stewart
93' U300/36
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