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blemon56 · 11-18-2011, 09:39 AM

I have a 2008 Class A with a ISC 360HP Cummins. Traveled across the states and to Alaska last summer. Drove from NY to south NJ the other day. I noticed that I kept hearing the engine fan cycling. Here's what was happening... On a basically level road at 60MPH with OAT 55 deg F, the engine temp would slowly climb to 210 F, the fan would engage and drive the temp down to 185 and the fan would shut off. Over the next 3 to 5 minutes, the temp would climb back to 210 and start the cycle over again. If there was a slight incline, the temp climbed faster. During a decline and at slower speeds, temp climbed slower. During this flux, the trans temp remained around 195. For 6000 previous miles, the engine temp and trans temp rose and fell together, and I only notoced the fan running while driving in AZ and NV with 100 deg OAT. I called Cummins and they said that if the temp did not exceed 225, there was nothing to worry about.

Will be driving back to NY tomorrow but the OAT will be in the 40's. I climbed under the rig and looked at the radiator for plastic or paper that might be blocking air flow. I plan to clean the radiator when I get back. Some folks think this is normal... but it didn't do this before. Any suggestions would be appreciated

dons2346 · 11-18-2011, 10:26 AM

Your fan controller is acting as it should.

I would look for the reason that the temp is climbing to 210. Do yo have enough coolant? Could be a bad thermostat. Could be a dirty radiator.

Seeing as how you were in Alaska, I would start with a good radiator cleaning.

blemon56 · 11-18-2011, 10:43 AM

The coolant level appears good. I've been reading the thermostat posts and plan to have Cummins take a look at both the thermostat and the radiator. Alaska is one dusty, dirty place, and I had the unit serviced at the Freightliner facility in WA. I just think that I would have noticed the temp flux driving from WA to NY in August. I bring up digital eng and trans temp on my dash while traveling. The fan sound is noticible. I'm a retired corporate aircraft mechanic and I notice suttle changes in noise and performance. Thanks for your input.

Mike Canter · 11-18-2011, 12:49 PM

My guess is your thermostat is just fine because if it was slammed shut it would be overheating and if it was jammed open then your motor would be running real cool. My guess would be your radiator is dirty.

powerboatr · 11-18-2011, 02:14 PM

your temps are exactly like mine and have been for over 15k miles(2008 MY)
no matter what the temp is outside.....
she will climb to 210 then the fan kicks in and cools down to the 190 ish range and the climb starts back up...yes if its cool out it takes longer.
if its 100 out it cycles pretty fast 2-3 minutes

if i run 67mph it seems to do it quicker
it i run 63-64 it again takes longer
all the while my tranny temps stay right at 100 over ambient
this summer when it was 105 on the road the tranny ran 198-205

i called and asked and was told here and at the Cummings place all is normal
i believe the dpf equipped engines, plus the neat electronics and emissions we must meet have forced engineers to run the engines a bit hotter than we are accustomed based on our age
i used to get nervous if the water went to 180....but that's OLD school
my 2010 F-150 runs 200-210 all the time

i will add, mine never gets above 212, even in the hot 105 days hauling the trailer and truck out back
it also cools down real quick once we stopp, and even faster using the engine brake.
I also try my best at 4k intervals to at least wash off the radiator front and back...
hope it helps

BobGed · 11-18-2011, 02:33 PM

Mine has done the same thing since day one. It is performing exactly as it should. Nothing to worry about.

blemon56 · 11-18-2011, 03:03 PM

Thanks for your replys... I agree that this may be normal... It just didn't work like this before. I understand the thermostat is variable, which I think means that it starts to open at a certain temp and goes fully open at a higher temp. I dont know how they fail... maybe partially open? I didn't pay attention to how fast the engine warmed up, and I didn't notice the fan cycling until a half hour into the trip. If the t-stat only opened... say half way, it might not let enough coolant through to keep the engine at a normal temp. A good question for the Cummins folks. I will update on any progress.

dons2346 · 11-18-2011, 10:10 PM

Quote:

Originally Posted by blemon56

.....................I'm a retired corporate aircraft mechanic and I notice suttle changes in noise and performance. Thanks for your input.

I am a pilot and I REALLY pay attention to changes in noise and performance.

Mr_D · 11-18-2011, 10:35 PM

Quote:

Originally Posted by dons2346

I am a pilot and I REALLY pay attention to changes in noise and performance.

Take offs are optional, landings are mandatory, unlike a car, motorcycle, RV, etc!!

blemon56 · 11-20-2011, 09:30 AM

Update - Traveled from S to N NJ (190 mi) at 60 mph and 50 F. The temp stayed between 185 and 197 for the first 100 mi. During the last 90 mi during hwy climb the temp went up to 215 twice and the fan kicked on and drove the temp down to 185. Sounds like things are fine but I still intend to clean the radiator when I get back.

Dutch Star Don · 11-20-2011, 11:31 AM

blemon56.......Is this a side radiator coach? I'm guessing that you're running a rear radiator model. I may be making too many assumptions because you didn't tell us, but most rear radiator coaches have solid fans that don't clutch or "kick on" as you said. If I'm correct (been wrong many times) it sounds more like a thermostat issue or a really dirty radiator that's causing the coach to get hot and you're seeing the frequent cycling of the thermostat.