Hi everyone,
I'm a new A4 owner (late model, 1977), definitely not a mechanic, and have been trying to find the source of water in my oil for a couple of weeks. I recently found that cylinder #4 has a tiny bit of water and isn't firing. I've read through all of the threads I could find but still stumped. Here's a summary:
* When I launched the boat this year (this boat, and any boat, is new to me this year) and checked oil, it was milky
* I have pressure tested the water jacket in the block, to 20 psi for an hour, pressure in through the water pump outlet and capped at the thermostat outlet to the manifold. Also pressure tested the manifold water jacket to 20 psi for an hour. No leaks.
* I changed the water pump to an MMI one, since the old one was leaking through the weep hole
* I also cleaned up and changed the gasket on the reversing gear cover, there was a lot of milk whipped up in there, and the old "gasket" looked like it would have let water leak in through the cover.
* I checked all of the exhaust, thinking that may be it. It's all in good shape with no blockage anywhere. Maybe a bit of a non-standard installation since there isn't a lot of room for vertical runs near the exhaust manifold. I made up a diagram, attached here, but I don't think this is the source of the problem. Have also tried iterations of closing the water through hull right after shutdown, but no change to water in the oil.
* I have changed the oil 8+ times, every time after making a change to some part of the engine, and it is still milky
* There isn't a lot of water, I can't notice any increase in the level at the dipstick after idling for 30 minutes or so, but there is enough to change the oil to milk
* There is a bit of water (a drop or two on the plug, and a few drops if I crank it out with the cylinder open) in cylinder #4, and that cylinder isn't firing. I *think* there is spark getting to that plug, but I have yet to confirm that directly. When I pull the spark plug wire while the engine is running, there's no change to idle, but there is a bit of discharge between the wire and plug when I pull it off. The plug has been dried/cylinder blown dry several times attempting to get cylinder#4 firing. I did have to clean up the inside of the distributor cap, which was corroded, and it looks like #4 had not been making contact (but it is now)
* Measured compression, around 100 +/5 psi on cylinders 1,2,3, and 65 psi on cylinder 4 (that goes to 75 with MMO in there)
That's about the extent of what I can test on my own. I spoke with a local mechanic who's an expert on A4's and he thought it was almost certainly a blown head gasket, although I don't know how that can be consistent with my block pressure test. I was thinking maybe a stuck valve could lead to low compression/not firing, and that could then lead to a bit of backstreaming water from the exhaust. I'm not sure how I can test that.
Mechanic also suggested that I could keep using the motor for the season, keeping an eye on the oil, and then change the head gasket once the boat is out.
What do the experts think? Is there something else I can (easily) check or do, short of opening up the engine?
I can also add that the engine temp was around 140F at idle, now it's around 120F or below with the MMI water pump.
Thanks in advance for any advice!
I'm a new A4 owner (late model, 1977), definitely not a mechanic, and have been trying to find the source of water in my oil for a couple of weeks. I recently found that cylinder #4 has a tiny bit of water and isn't firing. I've read through all of the threads I could find but still stumped. Here's a summary:
* When I launched the boat this year (this boat, and any boat, is new to me this year) and checked oil, it was milky
* I have pressure tested the water jacket in the block, to 20 psi for an hour, pressure in through the water pump outlet and capped at the thermostat outlet to the manifold. Also pressure tested the manifold water jacket to 20 psi for an hour. No leaks.
* I changed the water pump to an MMI one, since the old one was leaking through the weep hole
* I also cleaned up and changed the gasket on the reversing gear cover, there was a lot of milk whipped up in there, and the old "gasket" looked like it would have let water leak in through the cover.
* I checked all of the exhaust, thinking that may be it. It's all in good shape with no blockage anywhere. Maybe a bit of a non-standard installation since there isn't a lot of room for vertical runs near the exhaust manifold. I made up a diagram, attached here, but I don't think this is the source of the problem. Have also tried iterations of closing the water through hull right after shutdown, but no change to water in the oil.
* I have changed the oil 8+ times, every time after making a change to some part of the engine, and it is still milky
* There isn't a lot of water, I can't notice any increase in the level at the dipstick after idling for 30 minutes or so, but there is enough to change the oil to milk
* There is a bit of water (a drop or two on the plug, and a few drops if I crank it out with the cylinder open) in cylinder #4, and that cylinder isn't firing. I *think* there is spark getting to that plug, but I have yet to confirm that directly. When I pull the spark plug wire while the engine is running, there's no change to idle, but there is a bit of discharge between the wire and plug when I pull it off. The plug has been dried/cylinder blown dry several times attempting to get cylinder#4 firing. I did have to clean up the inside of the distributor cap, which was corroded, and it looks like #4 had not been making contact (but it is now)
* Measured compression, around 100 +/5 psi on cylinders 1,2,3, and 65 psi on cylinder 4 (that goes to 75 with MMO in there)
That's about the extent of what I can test on my own. I spoke with a local mechanic who's an expert on A4's and he thought it was almost certainly a blown head gasket, although I don't know how that can be consistent with my block pressure test. I was thinking maybe a stuck valve could lead to low compression/not firing, and that could then lead to a bit of backstreaming water from the exhaust. I'm not sure how I can test that.
Mechanic also suggested that I could keep using the motor for the season, keeping an eye on the oil, and then change the head gasket once the boat is out.
What do the experts think? Is there something else I can (easily) check or do, short of opening up the engine?
I can also add that the engine temp was around 140F at idle, now it's around 120F or below with the MMI water pump.
Thanks in advance for any advice!
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