Overheating, downshifting, and radiator cleaning

The following post was written to document our overheating problems and the excellent service we received at the Warner Truck Freightliner Center in Salt Lake City, Utah. We hope it may help other motorhome owners that may have such troubles.

[From Craig]  Since we started north through Arizona and Utah, our Alfa has been having problems with overheating. On I-17 between Phoenix and Sedona, and again between Sedona and Flagstaff, our engine temperature got high enough that the dashboard started giving us serious warnings. In neither case did it get high enough that the engine went into a reduced-performance protective mode, but it was touch-and-go for a few miles.

We tried to get the problem looked at by Freightliner Flagstaff, but they are quite dedicated to truck service and did nothing for 2 1/2 days out of a 3-day estimated time to repair, so we got out of there. An independent truck service center in Flagstaff changed our air cleaner and helped us try to clean the radiator, but this did not help much. We tried again to clean the radiator ourselves at Red Canyon Park near Panguitch UT and Bryce. We left a nice legacy of black diesel dust on the gravel spot, but even after two cleanings the temperature gauge remained touchy on any uphill grade.

There are experts on the Alfa internet forums who swear by Simple Green as a radiator cleaner, but radiators are made of aluminum and Simple Green slowly attacks aluminum. Simple Green HD is a more aggressive cleaner that is safe for aluminum. It is available at some Home Depot and Lowe's stores. 

Our cleaning helped with overheating, but more important was the fact that we learned to downshift the Allison transmission lower than 4th gear by slowing our road speed until the required engine RPMs were low enough for the computers to allow the downshift. At such lower road speeds, it's a good idea to turn on your 4-way flashers to alert other drivers that you're not able to maintain normal speed.

On our Alfa and most other engines, the speed of the fan that blows through the radiator is proportional to the engine RPMs.  To avoid overheating on uphill grades, the objective is to drive in the highest gear in which the engine can maintain the highest recommended RPM for sustained operation.  In our case that's 2500 RPM. It will be higher for gasoline engines and lower on some diesels.

By careful downshifting on uphill grades, we had an annoying problem under control.  At least until we made a wrong turn near Heber City while driving to Wasatch Mountain State Park.  We turned east on US 40 instead of west, which put us some long uphill grades, though less steep than we'd seen on I-17.  Performance of our CAT C7 engine just kept getting worse until we found ourselves in 2nd gear at about 20 MPH.  This kept the engine cool enough to avoid overheat warnings, until we finally topped a summit, upshifted and cooled back down while realizing that we were going the wrong way.  @&^*%&$%!

This fun ride convinced us that our cooling system needed professional help.  We made an appointment at Freightliner Salt Lake City for the next week, and took the flatter way around the Wasatch Mountains (west and north not east and north) to get there.  This facility is part of Freightliner's Oasis network, whose members are supposed to be nicer to RVers than their regular truck centers like the one in Flagstaff.

They were!  We arrived Tuesday afternoon, and got signed in to have our rig looked at Wednesday.  Their examination confirmed that our cooling system was  in bad shape both externally and internally.  Here is their list of recommendations, which we approved:

• Remove the radiator and CAC, then degrease and steam clean all 4 sides
• Replace fan belt and water pump belt
• Replace air cleaner again (the recently-new one wasn't installed right)
• Remount radiator and CAC
• Replace surge (overflow) tank
• Replace radiator cap + misc hoses and clamps
• Flush cooling system until outflow is clear

Now that doesn't seem like such a big list of things to do, does it?  Work started at 6 AM Thursday and finished at 7:30 PM Friday.  We were charged for 19 man-hours, which works out to a lot of money.  

CAT designed the C7 engine for use in the front end of a tractor cab, in which the top lifts off the engine and both the radiator and the CAC are easily accessible.  Then Alfa installed the engine under the sleeping bed in its diesel pusher RV, and built the rear end so that it just enclosed the radiator.  To quote the service report: "***VERY TIGHT ACCESS***".  If the engine had been designed to go in the back of an RV, it would take much less time to do this work.

The following images are courtesy of Robert Velarde of Freightliner SLC.  He seemed to be the service manager, but he also does all work on RVs.  This is an important reason for RV owners to choose Salt Lake City FL, a division of Warner Truck Centers.

This is the side of the radiator that faced the CAC and the fan:

Here's a closeup of the same side:

Remember, the fan had to try to blow air through this plus 3 more sides, two of which were comparably dirty!  It's amazing that there was any airflow. Robert said it was one of the ten dirtiest cooling systems he had ever seen, and that he was surprised we didn't overheat on the flat lands.

This is the same radiator cleaned up:

I forgot to ask Robert to get a picture of the junk that was between the Radiator and CAC. 

If you want to avoid a big expense like this one, Robert recommends having your radiator steam-cleaned once a year.  Hopefully also the CAC if you have a diesel.

Saturday we drove out of Utah into Idaho. The route included at least one hill that would have caused the Alfa to heat up in the past. We left all the shifting to the Alfa, and the temperature needle never varied at all after initial warmup. 

My tentative conclusion is that folks who carry on about vigilant downshifting are either 1) going through real mountains, or 2) in need of a good radiator cleaning.