P30 coolant disappearing?
It turns out there is no leak.
I've put about 17k miles on my 1998 Winnebago Brave since buying it-- including one 12k mile trip to AK-- and from time to time the coolant has been low. The previous owner changed the antifreeze some time during his ownership, not too long before selling it to me. The vehicle has never overheated. But with the coolant occasionally appearing to have disappeared, I began to think the system had a leak, and since I could find no evidence of an external leak, I worried the leak was internal; specifically I worried about the intake manifold gasket.
Yesterday, I went to Advance Auto and borrowed a cooling system pressure test kit and ran a pressure test. With this kit I pumped the system to pressure and it held just fine for two full minutes before I released the pressure. I call that passing the test.
So where is the coolant going? Well, not out of the system... I think the answer is that it is replacing air trapped in the system. This motor home has a feature that uses engine coolant circulated to a heat exchanger in the hot water tank so you have hot water when you stop during a drive. This feature works pretty well, but the hot water tank is higher than the engine. That's why I think the air is trapped there. It also explains why additional coolant is not drawn back from the overflow tank in the engine compartment: there is never enough vacuum created to draw coolant back through the hose from the tank. (Yes, I've checked that hose to be sure it isn't plugged or leaking.)
As far as I know, there is no bleeder installed in the coolant lines to the hot water heater tank, so my plan is to position the motor home with the front elevated while the engine cooling system goes through a couple of heat cycles and I'll bet the trapped air will come out. Luckily, there's a perfect spot to do that right here on my property.
First, though, I have to replace the t-stat. It has failed and is stuck open. That alone *might* be part of the reason the air never purged itself.
I'm posting this just as a resource for others that might search for information. Bottom line, stop worrying and test your system. Hope this helps someone.
I've put about 17k miles on my 1998 Winnebago Brave since buying it-- including one 12k mile trip to AK-- and from time to time the coolant has been low. The previous owner changed the antifreeze some time during his ownership, not too long before selling it to me. The vehicle has never overheated. But with the coolant occasionally appearing to have disappeared, I began to think the system had a leak, and since I could find no evidence of an external leak, I worried the leak was internal; specifically I worried about the intake manifold gasket.
Yesterday, I went to Advance Auto and borrowed a cooling system pressure test kit and ran a pressure test. With this kit I pumped the system to pressure and it held just fine for two full minutes before I released the pressure. I call that passing the test.
So where is the coolant going? Well, not out of the system... I think the answer is that it is replacing air trapped in the system. This motor home has a feature that uses engine coolant circulated to a heat exchanger in the hot water tank so you have hot water when you stop during a drive. This feature works pretty well, but the hot water tank is higher than the engine. That's why I think the air is trapped there. It also explains why additional coolant is not drawn back from the overflow tank in the engine compartment: there is never enough vacuum created to draw coolant back through the hose from the tank. (Yes, I've checked that hose to be sure it isn't plugged or leaking.)
As far as I know, there is no bleeder installed in the coolant lines to the hot water heater tank, so my plan is to position the motor home with the front elevated while the engine cooling system goes through a couple of heat cycles and I'll bet the trapped air will come out. Luckily, there's a perfect spot to do that right here on my property.
First, though, I have to replace the t-stat. It has failed and is stuck open. That alone *might* be part of the reason the air never purged itself.
I'm posting this just as a resource for others that might search for information. Bottom line, stop worrying and test your system. Hope this helps someone.
