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Old 09-29-2012, 04:17 PM   #1
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Angry Continued overheating

After several repairs that included new radiator, new fan controller, new water pump, two new thermostats we are still overheating due to fan not kicking into high speed. Please help winter may be on our horizon. Any comments appreciated! Thanks in advance. 40FDQS. 400 ISL Cummins
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Old 09-30-2012, 12:18 AM   #2
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Coupla quick thoughts:
1) when you unplug controller does fan default to high? If no then controller is defective or fan motor is not responding. If yes
2) have your tech splice into the valve on controller (one side will be ground, the other PWM signal from the controller. then drive it and record what happens on a big hill where your engine heats up; should go from ~20% duty cycle to 100% if it gets hot enough. If no then a) signal is not reaching the controller or b) controller is bad or c) fan is not responding.
3) test for 2c is to affix a an rpm meter to engine where it can read fan revs, then drive & record revs vs engine heat. Test for 2a is to probe the input lines for input signal varying from low to high. If 2a test is OK, and valve is getting signal out of the controller then there is likely a problem w/the fan motor.
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Old 10-01-2012, 07:41 PM   #3
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Thanks for the info. Does anyone know the pressure on the main pump for power steering and fan?
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Old 10-01-2012, 09:32 PM   #4
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power steering ~2500 at bypass, brakes 1000 when you tromp on it and shut off flow. These two are on a single flow-thru circuit that runs on 4gpm uniform flow on coaches prior to 08 m.y. & 5gpm on 08+ rigs.

Fan is on a separate circuit, & I don't know about flow for sure; I seem to recall its like 6gpm flow for the spec but I could be off on that. Then the thermostatic wax valve or electronic controller modulate flow to run the motor revs up.
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Old 10-02-2012, 08:49 AM   #5
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Curious--how do you know the engine is infact overheating? Have they confirmed engine temps separate from the dash guages and the on-engine sensor? Guess I would want an independent measurement before things get really expensive--maybe too late for that. Not clear on how the old wax valve controller varies from the newer electronic controls but if you disconnect and plug the fluid control lines going from the fan motor to the controller, you should get full speed fan [at full fan speed you should get engine cooling]--if not, your fan motor or hydraulic pump maybe the problem. If you get full fan speed but dont get effective engine cooling, the "problem" is elsewhere...If you are already beyond this point in the diagnosis, I missed it....sorry.
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Old 10-22-2012, 07:03 PM   #6
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What fan speed do you need for cooling? Thanks in advance.
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Old 10-23-2012, 06:00 PM   #7
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Per conversations w/WRV re: my 06FDTS36, idle fan speed w/cold engine should be ~850rpm. Just talked w/a service outfit working on somebody's 06, and they are getting 770, that's fine.
Hot engine climbing a hill you should have high 2000's, maybe 3000rpm. The engine produces a lot of heat from combustion & exhaust gas temp when pulling a long hill, and needs to waste that excessive heat.
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