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fan controller vs. thermostat

Yahoo Message Number: 47394
I'm having an intermittent overheating issue. I'll be driving 200+ miles when all of a sudden my engine temps will go above 205 ? sometimes as much as 230 degrees before the system starts to cool down. I'm thinking I have a fan controller issue, but that should be an ongoing issue ? this only happens on occasion. Sometimes I can go three days of driving with no overheats. Has anyone had similar overheat issues? Has anyone had a thermostat go bad ? Cummins tells me that is rare.
This is a situation that has been going on for 3 years ? each time I stop, the engine cools down on it's own, normally without a shutdown ? most of the time I can continue the trip without any additional overheating. I replaced the coolant temp sensor last week, air temp sensor checked out ok, but had another overheat this weekend on a 400 mile round trip. I'm at the point of replacing either the controller or the thermostat, but am thinking the thermostat is the culprit. Anyone have any input??

Thanks

Mark Peterson

03 Allure #30916

Re: fan controller vs. thermostat

Reply #1 –
Yahoo Message Number: 47396
I would go with the thermostat first. It sounds like it would be a whole lot cheaper than a controller.

Larry 03 Allure 30856

Re: fan controller vs. thermostat

Reply #2 –
Yahoo Message Number: 47397
Hi Mark P,

The best way to check the thermostat is with a Laser temp reader. Most auto parts stores has them. Also available at Harbor Freight. Shoot the laser beam on both sides of the thermostat housing and compare the temps.
Most all Cummins shop techs have one. I had a similar cooling problem. It ended up being the fan drive controller assembly.

At Red Bluff RV Park,

Chuck & Mary B

04 Windsor 02 Ford Ranger

Shelby Dog, Miss Kitty, Mr Lucky Cat

Re: fan controller vs. thermostat

Reply #3 –
Yahoo Message Number: 47401
Yes Larry, that is my thought as well. Just seems weird that the fan control would work well for a couple of trips, then stop for a short period of time, then go back to working. I think I should check wire harness to make sure that I don't have bad connections. Was thinking that someone else has had thermostat issues, but I just don't see anything showing up in the database search.

Mark Peterson
03 Allure 30916

Re: fan controller vs. thermostat

Reply #4 –
Yahoo Message Number: 47406
Yes, I had similar issues with my fan controller. Long story short, the controller was intermittent. When it would work and when it would not was totally unpredictable. Cleaning the connector contacts made no difference. I have an electronics lab in my business, so I removed the controller, built a mockup and bench tested it. Got the same results, random periods of normal and abnormal operation. It now rests with my other "trophies" of how not to design an electronic device. Replacing the controller totally cured the temperature swings, and gave me a huge bonus - from 7.5mpg to better than 10mpg. (Keep in mind I have a very light coach which has no slides, it weighs less than 26,000lbs empty and dry.)
Dave

2000 Allure

Cummins ISC 330hp
36' #30444

03 Allure #30916 wrote:

Re: fan controller vs. thermostat

Reply #5 –
Yahoo Message Number: 47407
Ah, the fan controller saga. Mine went intermittent on me this spring so I ordered a new one. My trophy now resides in the bone pile. I did make a modification to the mounting of the valve to facilitate the next replacement of the valve when (not if) it fails again. I had a bracket made to mount the new valve to and that bracket is bolted to the fan shroud box and not the valve. The bolts to remove the valve are totally accessible so valve replacement will be much easier than reaching inside of the box to get a the bolts.
Item to remember...If you are overheating and you think it is the valve unplug the 12v from the valve and that will force it to lock the fan on. Mileage will suck but it is better than burning up.

Regards,

Steve

04 Inspire #51075

Re: fan controller vs. thermostat

Reply #6 –
Yahoo Message Number: 47556
Below is my comments about the problem I experienced that I previously documented in message 27578 & repeated in msg 36336 (which first describes an opposite problem in response to a question, then in the 5th paragraph below may describe your coach's problem which I experienced on several trips and finally attributed it to a bad chassis battery!!!).

It could be the controller for the hydralic fan. Here a test I have used when I suspected that the fan was defaulting to max speed: Take a
8.5x11 inch piece of paper. Hold it up to the radiator grill. If it is
sucked to the grill, the fan is probably running at the "fail safe" full speed. If/when the fan operates at a slower speed, the paper will fall off.

I suspect that it is going into full speed mode and drawing down the temperature, when it should not be doing so. Several factors, as I recall, can affect the fan speed: a/c status, charge air temp, engine electronic thermostat, loose connectors, .... It also draws down your MPG by about 1 MPG!

If the fan is not going to full speed when the temp is going down, I would suspect a bad mechanical thermostat then.
I had the reverse happen -- engine sometimes would overheat, unless I pulled the fuse to the hydralic fan controller in the bay under the driver seat - would force the fan to high speed. The problem proved to be BAD CHASSIS BATTERY which was shorting out internally intermittently over rough US80 heading to Reno. At one point I pulled over at the rest stop, pulled the fuse, and continued home with the engine operating with below normal temperature, but never running hot.
In normal operation, my 2002 Allure temp would climb to 200/202, then drop to 190, and repeat -- always was a good feeling. With continuous full speed fan operation, the temp would drop into the 170's -- not good, but better than overheating.

I had ordered the various sensors to replace, but before I got to their replacement, it was suggested that it might be the chassis battery. Replaced it, and never a problem since.

(I would love to be able to monitor fan speed at the dash).

Herb

2002 Allure #30690 (at that time)
2007 Allure #31466 (now)

Quote from: jaynroark