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Old 08-31-2012, 12:57 AM
Jon K Jon K is offline
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More data points

Thanks to all of you for following up on this thread.

I finally got some time to continue gathering information, including what a Schraeder valve is, and why not to buy a bicycle pump at Walmart.

Here is what I know:

1. Engine loses coolant during regular use.

2. Engine stalls after 45 minutes to an hour of full speed, will not restart until it cools again.

3. Exhaust manifold cooling jacket holds 20 pounds of air pressure for 20 minutes.

4. Block cooling circuit from Obendorfer freshwater pump output hose to thermostat output coupling, with no thermostat, holds 22 pounds of air pressure for 20 minutes.

5. With the heat exchanger cap off, there are visible bubbles in the freshwater coolant, frothing when the engine revs to 2000 - 3000 rpm.

6. Freshwater pump looks good -- newish impeller and I sealed the gasket and tightened the screws.

7. Thermostat housing looks good -- cleaned and sealed the gasket, tightened the nuts.

8. Oil looks good -- no froth or other indication on the dipstick.

9. Cold compression test looks good -- no liquid, 90 - 105 compression.

10. Coolant hoses look good, and circuits test with good pressure.

11. Plugs are carboned, but mixture is rich.

So where is the steam coming from, and why does it lose coolant? At the beginning of this testing cycle there was no water or coolant in the bilge. Now of course there's lots because of changing the hoses and so on.

Where do I go from here? I could pressure test the heat exchanger, take her on a test run, or do the head gasket.

Is the head gasket a lot of work? I have access to the engine top and a few tools. The head bolts or nuts are rusty but I think they would come off.

If so, do I have the head machined or just add silicone to the gasket, or put new gaskets?

If I pressure test the heat exchanger freshwater circuit I might find air coming in. I could also replace all the hoses, although they and the heat exchanger look very new and clean.

I did hope that Neil was right about the exhaust cooling sleeve, but it holds tons of air. I got a tire valve stem, put it in a hose and clamp, and clamped it on. The other end I got a garden hose nipple, clamped it into a coolant hose, and added a garden hose close cap off my sprinkler to close it up. It took two tries tightening up until it held air, but the block cooling circuit and the exhaust manifold cooling circuit are tested without leaks. So I think it's not a cracked block, at least when cold.

Thanks in advance for your advice,

- Jon K.
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