Automotive-type heater (bus heater) on sea water cooled engine

[esarratt]

I figure this has already been figured out. I have a Volvo MD7A. It is sea water cooled.



Is there a way to make an automotive-type heater/fan work with this system or is it just too much hassle?


Thanks!

[Lepke]

Yes. Supply comes from the exhaust manifold and returns somewhere the suction side of the pump. The pump should be enough to circulate water thru the heater. You'll need a zinc or a wire bonding the heater to the engine. You should have valves so in the event of a leak, you can isolate the engine and keep running.

[esarratt]

Thank you for the answer. I was thinking of installing 2-4 of the radiator/fan combinations in series. 1-2 in the cockpit and 1-2 in the cabin. Do you foresee any problems?

[sailingabe41ds]

Just a thought....if you have a water heater that uses the engine to heat water why not tap into the water heater thus running a lesser risk of corrosion? Only thing is that is going to be more hoses and things that can break in addition to more fans. Your system will also only work when the engine is running.
Personally I think installing a diesel heater is the best way to go.

Abe

[esarratt]

I don't have a water heater. Hot water comes from a pot on the stove.


I follow your logic on corrosion though. Something to think about.



I actually have a small Taylors bulkhead mounted kerosene heater for the cabin.


I am just looking for an additional source of heat. I figured when I was running the engine, why not use a few car heater cores + fans to take advantage of the heat the engine generates.

[Dsanduril]

The big problem I could foresee is running hot saltwater through items not designed for that. We clearly do it all the time with heat exchangers on “fresh water cooled” engines, but those heat exchangers are usually very specific materials. Things like cupronickel and related families of materials. Because of costs, a straight off-the-shelf car/bus unit these days frequently has an aluminum core, and that might not be as suitable with hot salt water. If you can find a unit made of suitable materials… but most of the counter guys at the car shop aren’t going to know.

[sailingabe41ds]

My bad...I can see when you meant salt water cooled it also mean no heat exchanger.

abe

[Scubaseas]

Originally Posted by Lepke

Yes. Supply comes from the exhaust manifold and returns somewhere the suction side of the pump. The pump should be enough to circulate water thru the heater. You'll need a zinc or a wire bonding the heater to the engine. You should have valves so in the event of a leak, you can isolate the engine and keep running.

Careful with this as the flow of water changes direction when the thermostat opens. Volvo used a restrictor in the return hose (the one under the exhaust manifoldl ) that if left out or not included will ceate a hot spot on the head. I know several people with MD engines that ran into this problem.
Better might be to just run the coolant hose right before it enters the exhaust elbow and use that with a bypass valve to shut the heater off. Yes a bus type heater core will work fine. Not as lot of heat generated with that small of an engine though.

[Scorpius]

Running hot salt water through an automotive type heater? I expect it will last about a month before the pin holes develop in the thin aluminum tubes and hot salt water starts spraying all over the place.

However, it works well with fresh-water cooled engines with lots of anti-freeze, etc. (I have exactly that with an old bus heater on my Isuzu 240 and it's worked great for years). Maybe this is your opportunity and motive to switch to fresh-water cooling? - which is much healthier for your engine anyhow.

[Scubaseas]

Originally Posted by Scorpius

Running hot salt water through an automotive type heater? I expect it will last about a month before the pin holes develop in the thin aluminum tubes and hot salt water starts spraying all over the place.

However, it works well with fresh-water cooled engines with lots of anti-freeze, etc. (I have exactly that with an old bus heater on my Isuzu 240 and it's worked great for years). Maybe this is your opportunity and motive to switch to fresh-water cooling? - which is much healthier for your engine anyhow.

Exactly so. Sendure off engine heat exchanger and an electric circulation water pump (like Benz, Audi, VW and GM use these days) and Bob's you uncle.

[CarinaPDX]

I have my doubts that this is worth the effort. The water temps are fairy low on a raw water cooled engine (no steam pressure as in a closed system) and with a small engine there isn't a lot of heat to work with. I share the other concerns with corrosion - automotive grade heat exchangers are not likely to last very long. I suppose you could use cupro-nickel tubing and a 12V computer case fan to make your own heat exchanger to take a bit of chill out of the boat but I doubt it could heat even a 24' boat on a cold day.

Greg

[Jesse]

I did exactly what you are proposing with a Buhk Pilot 20. The heat realized was much less than had hoped for because raw water cooling has to be 20degrees cooler than fresh water cooling or you'll get salt deposits in the system and plug it up, and the the aluminum heater core only lasted 8months and 9days before corrosion destroyed it. After converting to freshwater cooling it worked perfectly but that required considerable jiggery pokery with the plumbing.

[Dooglas]

Originally Posted by Jesse

I did exactly what you are proposing with a Buhk Pilot 20. The heat realized was much less than had hoped for because raw water cooling has to be 20degrees cooler than fresh water cooling or you'll get salt deposits in the system and plug it up, and the the aluminum heater core only lasted 8months and 9days before corrosion destroyed it. After converting to freshwater cooling it worked perfectly but that required considerable jiggery pokery with the plumbing.

The voice of experience.

[capn_billl]

The automotive heat exchangers I'm familiar with are copper.

They should still be available in a junk yard somewhere.

[Lepke]

I'd be surprised if you can get enough heat for 4 heaters. It may be a struggle for 2.