ALLISON + COOLANT

I have a 2002 Winnebago Ultimate Advantage 40E equipped with a 350 hp Cummings diesel. I recently noticed that the engine coolant level was low. After adding a gallon of antifreeze and a gallon of water, I let it sit an hour. I then discovered the coolant level was down again, which prompted me to check the engine oil and transmission fluid levels. I found that the transmission was way overfull, telling me that the coolant is getting into the transmission.

I’d like to know if the RV (on a Spartan chassis) has a separate transmission cooler or if it is incorporated into the radiator. And, if it is separate, what does it look like? How do I get it out? What is the part number? And, finally, where can I buy it? Thank you.

Bob Venturini Pawtucket, Rhode Island

Bob,

Like most diesel pickups produced since at least the 1980s, the Allison automatic transmission in your coach uses a heat exchanger located within the engine’s radiator to help it stabilize fluid temperatures.

The internal heat exchanger is very efficient in removing heat, and it does double duty by warming the ATF after a cold start. Transmission temperature can vary greatly depending on how the vehicle is being used. Linking engine coolant temperature to transmission fluid temperature helps stabilize the large ATF temperature swings that would occur otherwise.

Whether coolant winds up in the transmission or whether ATF winds up in the engine coolant all depends on whether there is a pressure differential between the two systems and which pressure is greater. For example, if pressure inside the radiator is higher than the pressure inside the ATF cooler, coolant will flow into the ATF system when a leak develops.

I’m told the UA40E chassis is a rear-engine coach. I suggest visiting an RV repair shop that has a suitable lift. Then, raise the coach to allow the side-mounted radiator to come out through the bottom. You can pressure-test the radiator using an air pressure of 15 psi. If you see bubbles in the ATF cooling lines, you know the ATF cooler has a problem. With the radiator already removed, repairing the leak shouldn’t be that big a project, because any radiator shop can disassemble the radiator to remove/ repair the cooler. Flushing the transmission should be a step in the process before returning the coach to service. You want to get all the coolant/water out of it as soon as possible.

Other than rigging a temporary ATF cooler bypass to get the coach back to civilization, do what is necessary to repair and keep using the radiator’s internal ATF cooler. Good luck.