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Generator Coolant System on a Marathon
10-26-2017, 00:51 (This post was last modified: 10-26-2017 00:54 by cmillsap.)
Post: #1
Generator Coolant System on a Marathon
I wanted to change the generator’s coolant in my bus. So, I spent some time trying to figure out how best to drain the coolant system on the Kohler Marathon 20KW generator.

My Marathon XLII has a remote generator radiator. It is located behind the front bumper and is horizontally mounted on the floor and equipped with 2 fans that blow downward through a loosely woven screen to the ground below. There are two 1.25” steel pipes solidly attached to the radiator which drop through the floor and run back to and up through the floor of the generator bay. Those are the coolant delivery and return lines. The hoses you see in the photo are attached to those steel lines behind the generator.

Now, because the radiator is located at the lowest point in the coolant system, one would think that would be the best place to drain the whole coolant system. But “alas” Marathon did not provide a petcock on the radiator! Why they omitted a petcock drain on the radiator, I just don’t understand.

So, being somewhat baffled on how to remove the coolant, I gave up and called Marathon. Their instructions were to attach a pump to the hose nipple at the Engine Drain hose and pump the 5/6 gallons of coolant out of the entire system through the engine drain valve.

Now being somewhat familiar with how engine cooling systems work and forgetting to ask Marathon about it while I had them on the line, I’m wondering how that’s going to work with the thermostat closed on a cold engine. I’m guessing that the pump will pull the coolant from the thermostat housing backward through the radiator and through the engine and out the drain hose?
What do you think?


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İmage
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10-26-2017, 08:12
Post: #2
RE: Generator Coolant System on a Marathon
hope you don't have to remove the thermostat
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10-27-2017, 17:20
Post: #3
RE: Generator Coolant System on a Marathon
Most thermostats do have at least a small bypass port in them, so you should be able to pull the coolant out thru the engine drain hose. That being said, I would not be surprised to find you leave a gallon or so of old coolant in the system. You'll have to measure the removed portion to see how much is left. It may take a couple of flushings to truly get a clean system to then refill. The last couple of flushes I'd do with what ever fluid (distilled water, etc) you're going to mix the antifreeze with so then when you refill, you aren't contaminated with something else.
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10-31-2017, 12:40 (This post was last modified: 10-31-2017 18:27 by Hisham Amaral.)
Post: #4
RE: Generator Coolant System on a Marathon
With an 1/8 in bypass you will be draining the system by next week. It is much simpler to remove the stat and replace the goose neck with the gasket and then drain the system. Removing two bolts that hold the goose neck will take a few minutes that will give you the time to install a new stat when the new coolant goes in with everything up to date.
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11-03-2017, 00:28
Post: #5
RE: Generator Coolant System on a Marathon
So, being unable to drain the coolant system unless I disassembled it, I decided to follow Marathons’ instructions to connect a pump to the engine drain line in hopes that it would pump out the entire system. It would not. It would however pump about a gallon of coolant from the engine block and then quit pumping. I surmised that the closed thermostat would not allow the coolant to be pumped from the rest of the cooling system.

So, being uninterested in disassembling any of the cooling system, I took the easy way out. I pumped out the gallon or so of coolant in the engine block, refilled the system with the same type NAPA regular green anti-freeze 50/50 mix and ran the engine long enough to open the thermostat and thoroughly re circulate and mix the new coolant with the old coolant in the system.

I repeated the process until I had clean bright green coolant showing up in the expansion bottle. Using this method cost me a few extra gallons of new anti-freeze but saved me the work of having to disassemble the cooling system. Removing the thermostat on the engine was not a simple process and probably wouldn’t have helped in removing the old coolant in the remote radiator and lines anyway.

Marathon really should have installed a petcock drain on the remote radiator when they designed the coolant system. That would have made refreshing the generators’ coolant system much easier.


Chuck & Tela Millsap
Arizona
2003 Marathon XLII S/S
2000 Wanderlodge LXi S/S
2004 Wanderlodge M380 D/S
2000 Wanderlodge LXi N
/S
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11-03-2017, 22:19
Post: #6
RE: Generator Coolant System on a Marathon
Chuck,

That's the same process I used when changing the coolant on my DD S60. Assuming you can empty half with the generator engine petcock, after 3 flushes you'd be at 88% pure at 4 flushes you'd be at 94% pure. I did around 3 flushes on my S60 with a drain percentage of around 65% for a final purity of around 96%.

david brady,
'02 Wanderlodge LXi 'Smokey' (Sold),
'04 Prevost H3 Vantare 'SpongeBob'

"there is no perfect forum there are only perfect forums"
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