See signature for make and model. Isc 425 cummins.Have overheating issues in stop and go traffic. Fine on the highway even pulling the trailer loaded. So I take it to the local Kenworth dealer and they replace the thermostat. Cost $2200. Damn! I told them I didn't think the fan was running because last time it overheated I was backing in the garage and didn't hear it running. I can't tell driving down the road if it's running or not but can usually hear it in the garage. Seems to me if it was a thermostat it would overheat on the highway. So on the way home get stuck in traffic on the interstate. Stop and go and guess what? Overheated!Took it back to the shop and they are checking it out. Any ideas? Pretty pissed off about right now!Btw, I cleaned the CAC twice so know it's not that.

I have a 6.7 ISB cummins, last year I had a overheat alarm coming out of a campground and getting on the freeway. Later it would hit a overheat alarm whenever I climbed a grade . I took it to Cummins West in Sacto., where they replaced the Theromostat. Then they told me my computer control fan was non op and they sent me to Freightliner (they do not work on Freightliner parts????)Freightliner replaced the fan hub, 1600 bucks and end of problem. Of course that did not count what Cummins charged me for........zip!

Tell us how you cleaned the CAC. Is this a side or rear radiator chassis?

Thank you emorris. I think that could be my issue. I cleaned the cac by getting up under the mh and spraying it with a hose from the inside out. Rear radiator.

If this is a side radiator you can crawl under the radiator and look up on the back end you will see a 4x4 inch box. This is the fdc (fan direct control)electric box. There is a plug with one wire going to it. It is the ground. Disconnect it and the fan should go into high speed. If not then I would suspect a bad control. Mine was doing just the opposite, it was running all the time keeping my temp down to 175 to 181. It now runs 197. My part was $641.

I fail to see how the cleaning of the CAC helps engine cooling? On mine the CAC and radiator are in parallel. Wouldn't you need to be cleaning the radiator?

Overheating | Good Sam Community

Ivylog
Explorer III
May 20, 2015
If stopped in traffic for over a minute, you need to put the tranny in neutral. When stopped the torque converter is slipping creating heat and at idle you are not getting enough air flow.
Since this is a new problem and it does not do it at speed with the trailer, you need to clean your radiator/CAC better. Not sure if you have a crank case vent tube, but if you do you may need a slobber hose added to it to keep oil from getting into the radiator's fins. Do a search on cleaning and slobber tube for more info.
wolfe10
Explorer
May 20, 2015
sch911 wrote:
I fail to see how the cleaning of the CAC helps engine cooling? On mine the CAC and radiator are in parallel. Wouldn't you need to be cleaning the radiator?

With a rear radiator (likely Freightliner chassis) the CAC is in front of the radiator. The two are in SERIES. Dirt is "filtered out" by the CAC. So the front of the CAC is what needs to be cleaned.

Usual way is to clean from above (bedroom/closet access).

Blocked air flow into the front of the CAC also blocks air flow through the radiator.
C20
Explorer
May 20, 2015
I agree it's high. To access it they had to take the bed apart and use the panels in the floor. I know they had a lot of labor hours in it. Plus I didn't know they had to do that and had a bunch of clothes and in between trip stuff on the bed they had to move. Credit to them it was all put back right and even remade the bed. No greasy paw prints inside either!

When they get done if it turns out to be the fan switch we'll. be talking about a refund for the difference in labor hours.
Ivylog
Explorer III
May 20, 2015
hanko wrote:
$2200 to change a thermostat? That aint right

$2200 to put in a $48 thermostat, bend way over. $100 for new antifreeze so you paid for 20 hours of labor? And you took it back there?
You've owned it for over three years so this sounds like a new problem. Just using water from the wrong direction is not going to clean the radiator or the CAC.
hanko
Explorer
May 20, 2015
$2200 to change a thermostat? That aint right
sch911
Explorer
May 20, 2015
I fail to see how the cleaning of the CAC helps engine cooling? On mine the CAC and radiator are in parallel. Wouldn't you need to be cleaning the radiator?
koda55
Explorer
May 20, 2015
If this is a side radiator you can crawl under the radiator and look up on the back end you will see a 4x4 inch box. This is the fdc (fan direct control)electric box. There is a plug with one wire going to it. It is the ground. Disconnect it and the fan should go into high speed. If not then I would suspect a bad control.
Mine was doing just the opposite, it was running all the time keeping my temp down to 175 to 181. It now runs 197. My part was $641.
C20
Explorer
May 20, 2015
Thank you emorris. I think that could be my issue.

I cleaned the cac by getting up under the mh and spraying it with a hose from the inside out. Rear radiator.
wolfe10
Explorer
May 20, 2015
Tell us how you cleaned the CAC. Is this a side or rear radiator chassis?
emorris548
Explorer
May 20, 2015
I have a 6.7 ISB cummins, last year I had a overheat alarm coming out of a campground and getting on the freeway. Later it would hit a overheat alarm whenever I climbed a grade . I took it to Cummins West in Sacto., where they replaced the Theromostat. Then they told me my computer control fan was non op and they sent me to Freightliner (they do not work on Freightliner parts????)

Freightliner replaced the fan hub, 1600 bucks and end of problem. Of course that did not count what Cummins charged me for........zip!

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