Vanishing coolant

[Mickeyrouse]

Coolant is disappearing from my engine. It is a Westerbeke 55B,which is a marinized Isuzu 4LE2. I have replaced the pressure cap. I have gone over all hose connections and heat exchanger end cap repeatedly, yet find no evidence of drips. The drip pan under the engine is dry. The engine oil is clear, with no sludge or other sign of coolant getting in to the lube system. Coolant doesn't appear oily either. Since the engine only has about 150 hours since a new head gasket was installed, this lack of sign doesn't (at least to me) point to gasket issues. I've tried to run a pressure test with pressure test kits available at auto parts stores, but the 30-odd adapters don't include the type that fits my header tank.
I'm out of ideas. The only I can think of left is to pull the heat exchanger and have it tested, but that won't reveal any hidden leaks elsewhere in the system. Anybody have any new ones?

[Tupaia]

It would suggest the head gasket has failed. After only 150 hours, maybe the head was not re-torqued after initial run in or the mating surfaces were not in good condition. It is probably too late to re-torque the head now. If you are happy with the heat exchanger and the coolant isn't coming out and there is none in the oil there is only one place it can go, into the cylinders.

[Tillikum]

Who did the rebuild?

Did they provide run-in instructions and if so, were those followed?

If done by a shop, is there a warranty?

Was an OEM head gasket used or after-market?

Is the cooling installation the same as before the rebuild?

Try a compression test.

[Shrew]

It could be leaking out the raw water side of the heat exchanger.

[FPNC]

Try an automotive type combustion gas test kit at the coolant filler neck. These are cheap and easy and will tell you if there is any exhaust gas making its way past the head gasket and into the coolant side.

[Iron E]

It may be helpful to know how much coolant you're losing and when you're noticing it.
You will want to find a way to do a pressure test.

[Mickeyrouse]

I seem to be losing about a quart of coolant in 8 running hours.

[Cpt Mark]

Do you have a hot water heater connected to th engine for making how water while under power?

1 of my engines does this and I've come to conclude that the heater is much higher on a shelf than the engine. The engines coolant expansion tank was mounted just above the engine which is fin if there is not a hot water tank much higher,

[jkishel]

Rule out head gasket with combustion gas test at filler neck as mentioned above. If negative, check heat exchanger and exhaust manifold for cracks. Pressure test is best, but a cracked manifold may be visible with the heat exchanger stack removed. You may have to pull the manifold to thoroughly inspect it.

[srv express]

Originally Posted by Mickeyrouse

I seem to be losing about a quart of coolant in 8 running hours.

Care must be taken to preserve your new head gasket.
Running the engine a quart low on water is not recommended.
Running the engine on straight water without a mixture of 50/50 water /coolant is not recommended either.
IF you can't touch the cooling water with a finger then it is too low to run
for any length of time.

To diagnose this problem some running history needs to be figured out:

The engine was overheating and now with a replaced head gasket it isn't, Right?!! I'll venture to say overheating is the reason why the Head gasket was replaced in the first place. Replaced for the reason; the Heat exchanger is still leaking coolant into the raw water side.

Note:
The coolant side water is under pressure but, the Raw water side is not.

As a test I believe one could take the heat exchanger cap (Radiator cap on a Car) off, idle engine in neutral, watch for bubbles, idle engine in gear, watch for bubbles (if you see bubbles leaky head gasket or crack somewhere) and finally the hard part is watch for an hour or so to see if the water level changes (Most likely the water level will not change and likely overflow, indicating a leak in the heat exchanger).

One more hard to diagnose possibility is the Engine circulation pump needs to be replaced. Engine circulation pump has a hole in it called a weep hole inside the water pump pulley at the bottom of the shaft casing but, most would never be able to see it and when it leaks the water gets spun all over very hard to see. I would just replace it first regardless and then see if...

[Lepke]

Another way to pressure test if your coolant cap seats tight is to remove the temp sensor and install a tee with a gauge and an air connection. You may need a bushing from 1/2 to 3/8 and a valve stem. Using a compressor or bicycle pump add air until you're over the cap pressure and you hear it lift. It should purge down to the cap pressure and hold that pressure for 24 hours.

[srv express]

Originally Posted by Mickeyrouse

Coolant is disappearing from my engine. It is a Westerbeke 55B,which is a marinized Isuzu 4LE2. I have replaced the pressure cap. I have gone over all hose connections and heat exchanger end cap repeatedly, yet find no evidence of drips. The drip pan under the engine is dry. The engine oil is clear, with no sludge or other sign of coolant getting in to the lube system. Coolant doesn't appear oily either. Since the engine only has about 150 hours since a new head gasket was installed, this lack of sign doesn't (at least to me) point to gasket issues. I've tried to run a pressure test with pressure test kits available at auto parts stores, but the 30-odd adapters don't include the type that fits my header tank.
I'm out of ideas. The only I can think of left is to pull the heat exchanger and have it tested, but that won't reveal any hidden leaks elsewhere in the system. Anybody have any new ones?

Assuming you have a good exhaust elbow, right?