Overheating Issues – Freightliner 3126 with a Cat 350 C7

Last May we stayed in Laughlin, Nevada for a few weeks. When we left we took Highway 95 towards towards Searchlight Nevada. This stretch of road has miles of uphill and it was in the high 90’s that day. As we progressed on the route the coach started to overheat. I pulled over several times to allow cooling and just attributed this to the excessive heat.

Since that time we have periodically experienced overheating issues and I did my best to educate myself as to what might be happening. All the indicators led to dirty CAC and Radiator or bad regulators (CAT’s name for thermostats). So, I decided to start simple and periodically clean the rear facing surface of the radiator. Doing this was an excercise in futility.

Fast forward to two weeks ag0. We left our work camping gig in Custer, SD. bound for Des Moines Iowa to visit family. One of our legs of the trip deposited us in Dennision, Iowa. On the trip from Dennison to Des Moines the coach overheated badly in mid 80’s weather and high humidity. The last 150 miles or so were done at a top speed of 40-45 mph and I had to keep the transmission in fourth gear to keep the revs up so that it would take the engine temperature down slightly.

Upon arriving in Des Moines I made an appointment at Harrison Truck Centers and Freighliner Dealer in Des Moines. The next morning I took the coach in for repairs. They diagnosed the heating problems to a severally dirty CAC (Charge Air Cooler) and Radiator and said it would take about 12 hours to remove all of the air cleaner ducts, air cleaner assembly, and the associated cooling plumbing to the radiator and CAC just to get the parts out for cleaning and replacement. At this point we weren’t going anywhere in the condition we were in. I authorized the repair.

Radiator – Engine side – Note the debris and oil/dirt accumulation
CAC (Charge Air Cooler) – Back side facing away from the engine and towards the radiator

Besides the obvious accumulation road trash, note the oil and dirt embedded in the fins of the CAC. This was present on both the CAC and the Radiator.

This condition is inherent on the Freightliner 3126 chassis. What causes this is the engines oil by pass tube (aka: Slobber Tube). Cat engines use this tube to vent a small amount of oil mist to aid in performance (Hey, I didn’t design it). The problem with this is that the tube exits the engine and is aimed directly at the CAC and Radiator. Bad design. Prior to this major repair I re-routed the slobber tube and placed a large plastic bottle over the end of it to collect any of the oil mist that was expelled.

The back of the engine after removal of Radiator and CAC

After the repair I decided that I needed to do preventative maintenance to keep this from reoccurring but still trying to formulate how to get between the CAC and Radiator because the distance between them is only 1/2″. If any of you DIY readers out there have an idea on how to make one or where to purchase one shoot me a message.


  1. No help from me Chuck. Just wanted to share that I sold the Dutch Star this Summer and the new owner took it to Sturgis and the vacationed in Michigan.

    On the return trip the apparently the the windshield gasket has dry rotted and while driving 65 MPH into a stiff headwind the divers side windshield became the new front seat passenger.


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