Our diesel pusher with a rear-facing radiator kept overheating last summer, especially when climbing small hills. Initially, we rationalized that the two-speed fan wasn’t shifting from low to high, so we changed the fan relay to no avail. We didn’t want to climb the Rockies with this problem, so we queried a local radiator shop and was instructed to spray the radiator at the back with low pressure water from a garden hose. But first we should spray the face of the radiator with a spray cleaner like Spray Nine or Simple Green, let it soak in, but not let it dry before washing off. Then, we were to rinse with the low-pressure hose again. Hoping this solved the over-heating problem, we began our trek from the east coast to the Rockies. The problem of overheating remained as we entered higher elevation.

What does your heart and radiator have in common? They both push fluid to expel heat.

Next, we checked the fan clutch again by climbing under while the engine was running. The fan was turning correctly but the engine was still running hot. We contacted a fleet diesel shop in Pueblo, Colorado and were luckily squeezed in the next morning. Worrying about serious engine issues, fortunately the shop mechanic diagnosed the problem as extremely dirty fan blades. The mechanic used a low pressure setting on a pressure washer, climbed under the RV and scrubbed the blades clean for at least one hour. The culprit…oil from the engine breather pipe had deposited on the fan blades collecting dirt, sand and other road debris as we traveled across the US. Over time, this changed the blades airfoil shape. This is the same problem airplanes experience when moisture meets cold temperatures forming ice on the aircraft’s wings. The ice adheres to the leading edge and coats the top and bottom surfaces of the wing (airfoil), changing its shape and lifting properties. When air no longer passes over and under the wing supplying lift, the airplane stops flying. Vis-à-vis, the airplane becomes a flying brick!

When radiator fan blades become soil-laden, the fan turns but does not push air any longer, or at least not enough to cool the engine. Hence, diesel pusher radiators need to be inspected before long trips, regardless of season. Don’t forget to inspect the input side as well as the exhaust. Inexpensive radiator spray cleaners are available at auto parts stores, Walmart and on-line.

Make this a regular task

Save yourself a lot of angst and time…add this inspection to your pre-drive checklist! Your engine will appreciate breathing better.