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RV Tech Savvy: Biodiesel Concern

Originally Published in MotorHome Magazine



I’m a longtime Good Sam member and I have a question to which I can’t seem to find a definitive answer. What is the main drawback to using biodiesel fuel in a Cat 3126? I’ve inadvertently used it in our engine and it clogged the fuel filter after approximately 200 miles. This is obviously a drawback, but I’ve been told by Cat techs that it also will damage the engine internally. Due to the fact that biodiesel is becoming so widespread in the western states, I’m wondering how I’m going to find pure diesel out there.

Don Moffet | Clemmons, North Carolina


There are many formulations, blends and percentages of biodiesel fuel. Some biodiesel fuel is made from soy, while other types are made from fats or oils, etc. Generally, these contain somewhat less energy per volume than distillate diesel fuel made from crude oil. Some of the concerns involve problems with moisture (water) in the fuel, and microbes, along with faster oxidation and deterioration during storage. According to Caterpillar, biodiesel fuel that meets the requirements that are listed in Caterpillar’s specification for biodiesel, ASTM D6751, or DIN 51606, should pose no problems. I also found an older guide online at http://sebd.biz/Technical_Articles/CAT42001.PDF which covers this subject. The 3126 is an older engine and was designed before biodiesel became popular. I would try to stick with regular diesel or use the lowest percentages of biodiesel available at a station. If you follow factory recommendations, you should be OK.


Air Conditioning Quits

We own a 2006 Fleetwood Bounder 34F on a Workhorse chassis powered by an 8.1-liter Vortec engine. The dash air conditioning works great while the RV is in gear, but blows hot air when the RV is idling out of gear. How do I correct the problem?

Jim Boynton | Pasco, Washington


First, you need to narrow down the part of the system that’s causing the problem. I would begin by opening the hood as soon as the motorhome comes to a stop and have an assistant stay at the controls, and while stopped with the brakes on, shift from drive to neutral. Watch the front (center) of the air-conditioning compressor, and note if the clutch assembly is spinning or if it stops. If the electrically controlled compressor clutch is disengaging at idle, you’ll have to troubleshoot that circuit, which includes the relay and wiring. If it continues to spin at idle, look for the problem elsewhere. Another possibility is that the condenser (which transfers the heat to the air in front of the radiator) is either partially blocked with bugs and/or debris that may cause insufficient air to pass through when not driving. If it’s clean, determine if the electric auxiliary fan is coming on and blowing air through the condenser. If the fan is not working, there won’t be sufficient cooling at idle, and it’s even possible that the overpressure protection switch (which can be triggered when insufficient airflow causes refrigerant pressure to rise) may be shutting off the compressor. You can bypass the relay to make the fan run continuously when the ignition is on, for testing. Always stay clear of belts, pullies and fan blades.


Fuel Overflow When Filling

We own a 40-foot 2002 American Eagle with a 150-gallon fuel tank and fuel filler caps on both sides. When I refuel the motorhome, fuel belches back out unless I open the cap on the other side. This happens sometimes even after I’ve stopped pumping. Also, it’s very hard to get the tank to take fuel; the pump keeps cutting off as though the tank was full. When I open the cap on the other side, fuel runs out before the pump cuts off. This happens using pumps at a regular station (not a truck stop), and even when I use the slowest possible flow on the pump. I have to have my wife watch the other side and tell me when it runs over so I can stop pumping. This is annoying and expensive, aside from spilling fuel on the pavement, which has to be cleaned up. Is there a vent that might be clogged? Maybe there’s a fuel cap that will let the tank vent without spilling fuel?

Bobby Watson | Via email


This can be a real nuisance for owners, and those waiting in line behind you. Opening the cap on the other side provides a vent for the tank as it’s filled, and the need to do this indicates that the vent(s) are restricted in some way. Inspect the vent hoses; they should not have low spots where liquid fuel can collect and block off the flow of air. Also, make sure they are not kinked or otherwise pinched in tight-radius bends or where they go through tight spaces. You don’t want a cap that vents like that because if you park on a slope to one side the fuel would run out.


Battery Goes Dead When Disconnected

Have a tech question?I own a 2016 Thor Chateau 22B motorhome. Since I bought it new it has had a problem with the house battery going dead while in storage. I connect to shorepower and get it charged and then switch it to store mode, which is supposed to disconnect the battery. It will be dead and need charging within about a week or two. I had the dealer check it and was told everything was “within spec.” The engine battery does not die, nor do batteries on store shelves, so why would the house battery die if it is disconnected? Should I physically disconnect the cable?

Frank Olson | Colorado Springs, Colorado


Actually, all batteries self-discharge over time, even those sitting on a shelf, but it’s a much slower process that takes months, not days. I’m not sure what your dealer’s definition of “within spec” is, but you definitely have a problem, which should have been handled under warranty. It’s important to get this fixed as soon as possible because deep discharging will damage the batteries. Apparently something is not getting disconnected from the batteries and they are discharging. With the batteries in storage mode and the motorhome not plugged in to shorepower, measure the voltage going into or at the house fuse panel. It should be zero. If it’s not, and I strongly suspect that’s the case, bring this up with the service manager or owner of your dealership, and if you don’t get a proper resolution, contact the manufacturer. In a pinch, as you suggested, disconnecting one battery terminal or installing a mechanical disconnect switch will do the job for certain.


Ken FreundRV DIYRV TechRV Tech SavvyTech topics

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