Intermittent RV Overheating
August 7, 2012
Filed under Tech Tips
We purchased our 2008 Class A Itasca Sunrise 32H motorhome in 2007. It is on a 2007 Ford chassis using the V-10 engine and has been driven 47,800 miles. On five occasions during the past year the water temperature gauge has risen toward or into the red zone.
The first time it went into the “limp home” mode. This occurs on long hill pulls in cruise control where the transmission has downshifted and the rpm may be 4,500 to 5,000. I have placed a mark on the temperature instrument at “normal” so it is easy to notice any rise. The rise is from normal to hot in about two minutes. Pulling off the road and waiting a few minutes will bring the temperature reading quickly back to normal. There are no leaks or steam overflow.
Recently, we took our motorhome to San Tan Ford in Gilbert, Ariz., to try to resolve the problem. A service technician there found a Ford Technical Service Bulletin (06 21 15), and he installed a new thermostat and crossover tube. On our drive back home, as we reached the long hill climb at an altitude of about 4,000 feet and an outside temperature of 68 to 70 degrees Fahrenheit, the water temperature went from normal to about 9/10 scale (again in less than two minutes) before we disengaged cruise control and pulled over to the side of the road. By then the temperature was a full scale. Within a short time the temperature gauge returned to normal and we proceeded on home.
Several times last summer the air conditioner would stop blowing cold air at a strong volume and would blow reduced volume and warm air. It felt like an air vane had changed position or closed. We took the motorhome to Kayser Ford in Madison, Wis. The mechanic at Kayser evacuated the system and replaced the thermal cycling switch assembly. So far that problem has been solved, but I mention it just in case it has any correlation with the water temperature heat problem.
The main points are that this began in the last 12 months, not before, and the temperature rise is quick and then there is a quick return to normal. I mention all this in the hope that you or some of your readers who have had a similar experience may have found a solution.
– Byron McKean l Payson, Ariz.
Arizona is a challenging place for cooling systems because of the many long, steep grades and the hot climate. The rapidity with which the temperature gauge climbs and then shows a cool down causes me to question how it is functioning. However, the fact that it went into “limp home” mode further indicates there’s a real problem, so let’s look at some other likely culprits. Typically, hot running when climbing grades is due to insufficient airflow through the radiator or restricted water flow, such as internal clogging of the tubes. You didn’t mention if you hear the roar of the mechanical fan, or if the electric fan system is working when the gauge indicates the engine is hot. Since it cools down rapidly when you pull over, the fans are probably working, but they still need to be checked. I strongly suspect that the lower radiator hose may be collapsing shut when the water pump is moving a lot of coolant at high revs, and then when you pull over and idle the hose returns to its normal shape, allowing normal flow. There should be a spring inside it to retain its shape. This can be readily checked (when the engine is off and cool) by squeezing the lower radiator hose.
If a spring is there and the fans are working properly, check for any type of obstructions to airflow through the radiator, such as dirt, bugs, etc. Sometimes paper and debris get in between the air-conditioning condenser and the radiator. Also make sure any shrouds are still in place that direct air through the radiator. If everything checks out, there may be mineral deposits inside the radiator, reducing heat transfer. A radiator shop can help with this, sometimes the radiators can be “rodded out” rather than re-cored or replaced.
— Ken Freund