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Marathon Hot Water Webasto Engine Loop
This is a new to me coach, and I am trying to figure out the intricacies of the coolant circulation loops. My ultimate questions is, should the Detroit coolant pump force engine coolant through the hot water loop to the Atwoods WITHOUT the Webasto coolant circulation pump running?
I have read all the posts I can find using Giggle search engine. First learning was every converter did it differently. I have found posts where folks were discussing Marathon conversions specifically, and said that the Webasto must be enabled and coolant pump on. The logic was that once the coolant reached the cut in point of the Webasto, the burner would not fire but the pump would continue to run. That seems jacked to me
Here are my facts.
All coolant valves are open.
The system has been burped and high volume transfer pumps used to circulate coolant in both the hot water and coach heat loops.
The Webasto definitely heats the water in the Atwood’s when it’s activated.
BUT just running down the road does not circulate coolant to the Atwood’s.
I do not understand why. There is a coolant loop that leaves the discharge side of the Series 60 coolant pump that feeds directly to the intake of the Webasto loop going to the water heaters. I do not understand why that is not enough to circulate coolant through the water heaters. It was enough on two previous series 60 coaches.
Any insight is appreciated
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2 Replies
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You need to press the 12v water heater button or 12v heat button which is in your closet probably above the toilet.
That opens the flow to run in cold weather to engage your heat registers and allow the hot water into the loop.
Press the 12v button.
Did you receive a Marathon book with your bus?
On my 07 I ran with the 120v water heater engaged constantly and always had hot water while under way and when parked that is what you want. I was probably not exercising my Webasto enough.
Later
bv
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Thanks Bernie. I have the book, and I have stared at the schematics.
The issue is I don’t want to do that. I know from prior ownership that it is possible for the engine water pump to provide enough flow to the hot water heaters to have hot water when you get there.
So why don’t I want to do that. One I might forget to engage the button at the start of a drive. Even if I do, the Webasto will burn fuel until the engine coolant gets hot enough to open the Webasto tstats. Two, and the biggest factor, is that I may forget to turn it off once we get to the destination.
After staring more, I now understand that is NOT how this system is piped. I will attempt to attach a marked up schematic which shows the issue. The supply for the Webasto and the return are deadheaded against one another in the area in red. There is no motivating force to circulate the coolant. I am going to have to replumb to get what I want.
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