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Old 16-07-2021, 08:20   #31
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Re: How much coolant loss is normal/acceptable?

Originally Posted by JPA Cate View Post
We did have coolant loss, about 3 yrs. ago, now. Normally there is none.

It was from the heat exchanger. Jim saw it right away, upon starting the engine, and looking astern. Our coolant is green, and it was quite obvious on the water.

We had to replace the whole exchanger, rather than repair the inner bits, because of marketing issues, and wanting to get the engine functioning quickly (living on the hook).

Yeppers~ Iíve got the same engine. On the J4ís, the coolant manifold cover is aluminum - it wears out and need replacement after a few years. Part cost is $1200 US!
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Old 16-07-2021, 10:51   #32
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Re: How much coolant loss is normal/acceptable?

Zero coolant loss is the norm, anything else and you need to track & fix.

There should be a set of isolation valves between the engine & your hot water tank. If there isn't, then install them - and close them. If the leak stops, then it's likely the hot water coil - if not, you know it's within the engine circuit.
- Should always have isolation vales on auxiliary loops like hot water tank, or cabin heaters so you can close them and keep engine running despite hose/coil failures.

If there's no obvious coolant in the bilge, then I'd put money on your heat exchanger. Pull it and take it to a radiator shop to get pressure tested. looking for bad gaskets as you remove.
Next most likely is a head gasket - at least you'll have the heat exchanger out of the way.....
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Old 16-07-2021, 23:14   #33
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Re: How much coolant loss is normal/acceptable?

I had a coolant loss problem once - turned out the heat exchanger cap valve was opening under pressure to let coolant out into the expansion tank but not allowing it to draw back when things cooled down. It became obvious when the expansion tank overflowed on a very long wind-free trip. So for a potentially easy win, check or change the cap.
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Old 17-07-2021, 08:16   #34
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Re: How much coolant loss is normal/acceptable?

Originally Posted by Cadence View Post
I hope it doesn't happen. I wonder how many PPM is detectable by taste or lethal over a prolonged period?

I wonder if there is something a kin to a litmus test that would be more definitive than taste?
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Old 19-07-2021, 05:54   #35
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Re: How much coolant loss is normal/acceptable?

our yanmar 3JH4E had the same issue: level in 'overflow tank' was lowering, couldn't figure out where the leak was. the easiest way to check for a leak without running the engine is to buy a STANT tester at an auto shop. the stant is a hand pressurizer whose cap fits the cap on the yanmar 'freshwater' tank aka radiator. with engine cool, install the stant. put paper towels under every conceivable joint (hoses into heat exchanger, hot water heater, thermostat body etc. pressurise the stant. at about 7 psi i saw delco colored antifreeze shooting out of an area on the underside of a hose off the engine block that was part of the heating loop into the hot water heater. when the engine was runiing, this hose was hidden behind a bulkhead between engine compartment and hot water heater on my nauticat 321. Rx had to replace both water heater hoses; at the sme time i decided to do a coolant flush and clean the heat exchanger. (be sure to order the specially formed ht ex gaskets from yan mar before you do this, as the old ones tear when you take them off. )
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