Being new to Cummins, not diesels, I have a question. My coach is equipped with a 2008/7 6.7 300HP ISB engine. When I am running down the highway it usually stays right at 190 to 192 degrees. The other day I was easing around very on non interstate roads and I saw the temperature beginning to rise all the way to 212 degrees then it rapidly returned to the 190 degree range. I figure the fan cut speed down when I was easing around and then cut in when it reached 212. Is this normal. Several friends I have talked to say theirs never fluctuate. BTW, I was on flat terrain with no load. Any input? Thanks

Hi Higgins,

I have an 07 Monaco Camelot 40 PDQ with a Cummins ISL400, and it's doing the same thing. Prior to the inital attempt to correct this my coolant temp would rise to 208 and the fan would come on. The temp would continue to rise to about 212 before the effect of the fan kicked in and then drop to 190-192. It did this every 45-50 seconds (flat ground constant load) Monaco had Cummins reprogram the engine fan setting from fixed to variable. Now basically it does the same thing with temps between 204 and 192 every 30 seconds. Monaco is looking into it with Cummins.

My 6.7L 350HP ISB coolant temperatures fluctuates as you described, especially in warmer weather and when heavily loaded (grade pulling). When operating on the flats it doesn't change much. Remember your 2008 engine is an emissions engine which will operate differently than previous model years. Remember back when gas engines went to emission controls the first thing we all noted was the higher coolant/operating temperatures that were required to meet the standards, now we are seeing it in Diesels. I believe what you see is a perfectly normal occurrence for your engine.

Spike

These engines have a modulating thermostat which ranges between 180-200 degrees with a specified maximum top tank coolant temperature of 225 degrees.

I have an ISC,360 hp. with 92oo miles.
At 68 - 70 mph the temp ranges from 174 to 216.
On the high side the fan comes on and cools the engine down.
About every 8 to 10 minutes......all day long.
At 82 mph the temp stays at 186 degrees.
In construction zones I noticed at 50 mph the temp is between 184 to 186.
Go figure..........

Just finished a conversation with Jason at Horton Fan Clutch Company. I'm told they are going into production of a "Stratus Viscous fan clutch.......... [http://www.hortonww.com/products/products.asp ]
Hopefully something like this will result in less noise, distraction and stress on our engines.
FLCC should have used an variable speed fan in first place.