[Richard]

Thanks for the clarifying info.

Then the heater core is likely your culprit. Open your generator bay and inspect the ceiling. White paper towels are your friend in this case for finding coolant leaks. The core is directly above the gen bay, and since water/coolant generally obeys the laws of gravity then what you reported makes sense. Yours would not be the first core to fail.

Here comes the good news/bad news. You can keep those valves shut and still use the coach. Obviously you will lose dash heat AND the engine coolant circulation through the AH. If you can figure out which loop is for the AH you could open those. If I knew which valve was which I would say. The bad news is I think replacing the heater core is going to be a CHORE. I would try to get some advice from Newell.

[RussWhite]

My coach is being cared for by another guru. So, I cannot take a pic for you and I just looked through my hundreds of images and did not find one of those valves. But I am sure mine were labeled so I knew which to turn off to isolate the dash heat. When you get back to your coach and have settled down from the stress of the coolant loss event, get a good light and a rag and see if you can't uncover a label. Russ

[pairodice]

Thanks guys! I will go to the coach this afternoon (work keeps getting in the way!) and check the valves and as per Richard, I will check the genset bay because that is where all the juice was flowing from.
Quick question - since I lost most of the fluid - should I just fill the system up with water to test leaks and then once I figure it out go back and refill the antifreeze?

[Richard]

My input, sample size of one, is that it depends.

When was the last time the coolant was changed? Are you running conventional or ELC?

You say you lost most, but the remaining coolant is indeterminate. Did you add coolant or water to limp home? If water, was it distilled water or creek water?

My thinking is that you can keep the valves closed, remove the hoses from the valves, and do all your testing without involving the total 17/18 gallons of coolant in the system. When you get the hose to front/heater core water tight, only then do you decide to flush and refill OR top off what you have.

[pairodice]

I finally (had to work longer today again) got the coach up on the wooden platforms that raise the front end up about 3” by the tires. So now I have to figure out where to put my jack stands under the front of the coach… I will go revive my ongoing ‘Where do these jackstands go?’ Thread…
Thank you Richard for your Sage advice as always. I doubt this fluid has ever been changed before, certainly not since I’ve owned it… I have no idea what type of fluid is in it - I generally buy the Prestone Green stuff 50/50 mix…
Are you saying I should leave the coolant as is, turn on the valves one at a time until I see some juice flowing and then I know where my leak is? Then turn the valves on/off one at a time until I find the culprit?

[pairodice]

Looking at the valves from the back of the coach towards the front): the engine is NOT leaking coolant currently and the front heater core is not leaking with valves 1,3,4 in the closed (counter-clockwise CCW position) 
Valve 1: when I turn it ON (counter clockwise) I can hear coolant draining from the engine coolant reservoir. Runs from the engine water pump???
Valve 2: already open - must go to the engine… not sure… runs from a coolant filter to???
Valve 3: closed CW - this runs from the exhaust header afaik
Valve 4: closed CW - runs from the exhaust header

[Richard]

Ok, first you don't put Prestone 50/50 in that diesel engine. Do some research on proper coolant packages to prevent cavitation on the cylinder liners.

No on opening the valves to check for leaks. Keep the valves closed. Disconnect the hoses from the valves. Rig up some fittings for the hoses so you can circulate water and check for leaks. When you find the leak and get it repaired. Reconnect the hoses and decide what to do with coolant.

Coolant is nasty to work with and TOXIC if ingested. That's why I would prefer to work just with water until you find the leak.

[pairodice]

Rats, the last guy that looked at the engine suggested the Prestone 50/50 for it afai recall…
I’ll plan to change out everything - the good news is that we have only put several 1000 miles in the past 5 years or so :-( …

[pairodice]

Found some threads about using both SCA and OAT coolants… not sure which is best - I like the idea of not having to change fluids ($$$) very often but is there a downside to using either? I talked to Newell this morning and they said it doesn’t matter as long as it’s green… ???

[HoosierDaddy]

There are SCAs available to minimize cavitation. I have used test strips to measure for sufficient cavitation protection and ph .