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12-06-2013 12:09 PM
Re: Yanmar 4JH-2E using coolant

Simple, cheap and effective way to check - put dishwashing soap in the coolant tank.

If you blow bubbles you have a leak in the exhanger.

Same thing works to make sure your impeller is working (if you have an under water exhaust) - soap the impeller - crank the engine and look for bubbles.
12-06-2013 12:06 PM
Re: Yanmar 4JH-2E using coolant

Possibly a small leak from the coolant piping inside the heater into the fresh water supply? Generally, after the engine warms up there is pressure in the coolant system, assuming you have the filler cap secured. If you taste the hot water and is sweet, it has coolant in it. As the anti freeze is toxic, don't taste too much of it, maybe a drop on the end of your finger? or, as mentioned earlier, use a fluorescent dye in the coolant, safer that way.

Paul T
12-06-2013 10:52 AM
Re: Yanmar 4JH-2E using coolant

This post is old, but relevant to me maybe. Could you elaborate? How can the hot water heater be related to the fast use of coolant by the yanmar engine? Thanks in advance,

07-14-2011 11:28 AM
Beersmith I have the same engine and had the same problem. Turned out to be the hot water heater.
07-12-2011 08:07 PM
jrd22 I think I would try to isolate where the leak is by disconnecting the lines to the hot water heater. If you are still using coolant then it's got to be engine. You said that there was no pressure in the overflow with the cap off while running but wouldn't it be more apparent if you left the cap on so the pressure built up? There is a way to check if exhaust gases are present in the coolant, an automotive parts store should have it.
07-12-2011 06:47 PM
Originally Posted by dabnis View Post
Assuming there is water in the bilge, I have read that dogs will drink it because it is sweet? If you don't want to taste bilge water there may be some sort of dye that will show up under an ultra violet light?

Ultra violet leak detector: Black Light World - Fluorescent Tracer Dyes

07-12-2011 06:07 PM
dabnis Assuming there is water in the bilge, I have read that dogs will drink it because it is sweet? If you don't want to taste bilge water there may be some sort of dye that will show up under an ultra violet light?

07-12-2011 03:43 PM
Tim R.
Yanmar 4JH-2E using coolant

Here is what I know:

- Engine runs very well with ample power at all rpms
- I have to top off the overflow tank after every 4 hours of motoring
- No overheating(yet)
- No coolant in oil(crack in block)
- No pressure in heat exchanger when running the engine with the cap removed(bad head gasket)
- No apparent leaks under the engine

What is left are the following:
- Hot water heater leak
- Heat Exchanger leak
- Exhaust riser leak
- hidden leak into bilge
- Something I am missing?

Any of these should have coolant in the bilge, hot water system or the exhaust. Does anyone know of a way to test for coolant(trace amounts) in water?

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