We've got a '93 Breakaway with a 230hp Cummins rear-cooled diesel engine. On several recent trips (including our jaunt down to Milford) I noticed the engine coolant temp spiking over 200 degrees. Shifting into neutral and revving the engine helped. On the way home, I downshifted from 5th to 4th gear and that brought the needle down to the 185 degree range, and it was steady for the rest of the trip.

That suggests several things:

1. The extra rpm could be overcoming radiator fins that are becoming obstructed with oil residue being blown off the engine, making it harder for air to pass through,

2. The fan blades themselves might be accumulating oil residue and messing up the design airflow over each blade,

3. The fan belt (which is getting dried out according to MWrench (Ed) when he reached in there to check it for me) might be slipping once in awhile.

Some of the remedies I will try are as follows:

1. Wash out the engine compartment, including the radiator, with a good cleaning agent. (Ed suggested Simply Green using regular garden hose pressure; not a high-pressure sprayer. We talked about being careful not to bend the cooling fins as that can make a huge difference in the air passage).

2. Replace the serpentine belt (which is probably overdue anyhow). This will give me a new start for total time on the belt, and will give me a spare to throw in the basement for backup in remote locations.

3. Ed noticed the coolant hose coming off the radiator actually goes up before it goes back down to the engine (!), and that could cause a vapor lock.



I'll reposition it and then get a shorter hose to continue the flow (good catch, Ed!).

Apparently good cooling isn't just a matter of checking the coolant level from time-to-time. You have to check the entire system for component function on a regular basis.

Results of these remedies to be published when they come in,

Lou

Do you have a tach? If i let the rpms drop too low in any gear, (lugging the engine), my temps go up in my MCI bus. Besides keeping an eye on the tach i also watch the exhaust for black smoke which is another sign of lugging.

Lou, I did notice black smoke more so when we started and less as we traveled as I was behind you the whole way. On the Mercedes listserv, they talked about the Italian tuneup which was to get on an open road and put the pedal to the metal several times running it up as fast as you dare. I could see where low RPMs and lugging could contribute to the overheating but not saying that is the case here.

Rear-radiator pushers' radiators are subject to crud being thrown off the highway into the radiator. Before any long trip, I blowout the radiator with air, then wash it. Patience is needed, as the hose has to be kept in contact with each area long enough for the cleaning solution to go all the way through.

Yep, I stood there this afternoon with soapsuds coming out until I thought they were being manufactured!

I drove the coach 15 miles and worked the gears (5th for cruise and 4th for small hills). Stayed on 160 degrees the whole time with no pegs. On seeing the old serpentine belt which had a myriad of cracks on the inside I figure we must have had some slippage at times on the way to Milford.

Thx,

Lou