Hot Water Engine Heat Exchanger

[xpjet96]

I have a water heater that uses an engine heat exchanger to heat the water while driving down the road. Access to the water heater is not insulated inside the cabin due to access requirements. Problem is that while driving in warmer temperatures (near 100 degrees in Iowa and South Dakota last week) heat is emitted making it difficult to get the air cool in the cabin. I like the feature, but would like to know if there is a bypass in the engine compartment or at least a way to add one. Can't find any reference in the manuals.

[Harvey51]

Perhaps off topic.
A few years ago we were camping in Banff national park when we smelled antifreeze inside our van and not long after it was squirting out of the heater area under the dash. With jugs of water we made it to a good sized town out of the park (Rocky Mountain House), stopped at Canadian Tire, which didn’t have a heater core or time to install one in the next couple of weeks. We were directed to Dick’s Fleet repair and found out that it would take at least a full day of work and they couldn’t start for a week. But they could short circuit the heater hoses to bypass the leaking heater core - in an hour! Wow, if I lived near Rocky I would be getting all my mechanic work done at Dick’s. Yes, I did contribute doughnuts. The only part needed was a short plastic pipe larger on one end because the outgoing and return hoses have different diameters. So one more part for Jaxdad’s suggestion.

We got home in comfort as it was summer time. Eventually I tackled the job myself and the 1992 GM van is still running well, including heater and air conditioner.

[Old-Biscuit]

JohnyWalter wrote:
Hey
My old hot water heater is AC and heat exchanger. I run AC when it's available, which makes it easier for the engine to maintain temp rather than heating cold water.
Jon

RV Water heater with 'motoraid' heats the water WHENEVER engine is running........coolant flows thru heat exchanger when engine is ON

[JohnyWalter]

Hey
My old hot water heater is AC and heat exchanger. I run AC when it's available, which makes it easier for the engine to maintain temp rather than heating cold water.
Jon

[maillemaker]

More than likely your motor aid (and also your coach heater driven by the engine) are teed off the main heater core circuit for the cab. If so, you don't need a bypass circuit for the 2 lines going back to the house.

Steve

[xpjet96]

Thanks! I think that would be doable even for me. Only other option is to try and insulate the compartment. May end up doing both.

[JaxDad]

Don’t forget to add a bypass not just shut off valves. If you merely deadhead the supply line you can create problems. The coolant system is designed to have a certain amount of circulation even when the heaters are in the ‘cold’ position. Bypass ALL of the remote heat, especially the dash heater.

You need 2 T-fittings, 2 ball valves and a bit of hose. Put a T fitting in the supply line with a ball valve just downstream of the T fitting. Then connect the 2 T fittings with some hose with a ball valve in the middle.

Summer time the ball valve in the bypass line is opened and the one in the supply line is closed. In cool weather the positions are reversed.

A bypass setup will also keep the dash A/C working FAR better.

[garyemunson]

Winnebago has been using that "Motor-Aid" water heater system for quite a while. Haven't seen any with valves but would be a good idea in your case.

[Old-Biscuit]

Coolant lines to water heater heat exchange tubes do not have shutoff valves.
You always have to pinch coolant lines closed when disconnecting from the water heater.

Logic and RVs do not coincide.

[xpjet96]

Sorry, finally took the time to update my profile to reflect equipment. I posted earlier rather quickly and didn't think to put down rig type, but made a bad assumption that posting under Class C said enough. Thanks for the responses so far.

I have to run up to the truck service center where I get the chassis taken care of and I'll have them look at it as well to see if a bypass could be added if there isn't one. I looked around where it appeared the lines are being routed and couldn't find any type of valves associated.

[Jim]

No idea what engine or even the year of your RV since it's not in your sig or profile so just throwing this out there...with diesel pushers, they always put gate valves on the engine to shut off the coolant that goes to the dash heater. Develop a leak in that heater system and it's a simple matter of shutting off two gate valves, top and bottom of the engine. That way you're not dead on the road. Makes sense, doesn't it? It's happened to me, puked antifreeze for 3 miles until I could pull off the freeway and shut them off.

OK, so now with your system, it seems logical to me that they'd put a couple gate valves on that system too, near the engine. So maybe climb under there and follow the hoses back to the engine and check that.

[Old-Biscuit]

No valves on the coolant lines to/from water heater.

You could add one on coolant line to water heater and shut the flow off.

Just valve it in when you want to take advantage of that free heat

AND remember that both lines would still have coolant in them IF you did any work on water heater that required disconnecting them at the heat exchanger tube.