Do I have a blown head gasket?

[MikeB]

I just finished with the manifold and block pressure tests, both held 20psi for about an hour.

The reason for the sketch’s

I was thinking maybe the exhaust hose from the muffler to the transom is too high above the riser causing what water is left in the the hose to flow backwards towards the riser once the engine is turned off.

The y valve idea was a theory to save the water pump from running dry for the last 15 or 20 seconds of the engine run to blow any remaining water out of the exhaust hose. But Neil is right and I didn’t think of it but that could harm the muffler running it dry.

I checked the water injection port and it is about a 4 inch nipple that looks to reach just below the 90.

I ran the engine for a combined few hours yesterday while I did more oil changes and again today for about an hour. Everything seems to be working fine but I was shutting off the seawater intake before shutting the engine down.

[ndutton]

I was thinking maybe the exhaust hose from the muffler to the transom is too high above the riser causing what water is left in the the hose to flow backwards towards the riser once the engine is turned off.

If that were the case wouldn't it happen every time the engine was used? Since the boat came from the factory?

No, your cooling system pressure tests and compression test confirm everything is intact, your exhaust system drawing tells us it is properly done and your assertion the raw water thru-hull was closed during prolonged cranking eliminated backflooding through the exhaust as the cause of your watered down oil. So what's left? How did water get into the oil?

Post #1:
. . . . while doing the dishes after dinner the fitting under the sink burst spraying fresh water all over the engine compartment and all over the A4.

You have enjoyed 200 hours of trouble free motoring until this episode (save slightly elevated temperature) and now all of a sudden there is water in the oil. Cause and effect. You should probably check the anti-siphon valve for proper operation too.

About the elevated temperature, I suggest it is probably time for a heat exchanger disassembly and cleanout. While you're at it you might consider MMI's new thermostat too.

[zellerj]

Water in the oil

The only time I got water in my oil was when I was anchored next to a busy channel and boat wake smacked the stern, forcing water through the exhaust system and into the engine.

When you were anchored, could that have happened?

[Sam]

Similarly, I was in heavy following seas for about 20 miles and water intruded into the engine. I don't recommend this for everyone but I put a large lever ball valve inline of the exhaust hose easily reached through a rear lazereette. I have only activated it a few times in the couple of decades, problem never returned. [You MUST remember to open it before you start the engine]

[joe_db]

If that were the case wouldn't it happen every time the engine was used? Since the boat came from the factory?

No, your cooling system pressure tests and compression test confirm everything is intact, your exhaust system drawing tells us it is properly done and your assertion the raw water thru-hull was closed during prolonged cranking eliminated backflooding through the exhaust as the cause of your watered down oil. So what's left? How did water get into the oil?


You have enjoyed 200 hours of trouble free motoring until this episode (save slightly elevated temperature) and now all of a sudden there is water in the oil. Cause and effect. You should probably check the anti-siphon valve for proper operation too.

About the elevated temperature, I suggest it is probably time for a heat exchanger disassembly and cleanout. While you're at it you might consider MMI's new thermostat too.

I am going to agree with you about 98%. I doubt the boat has been flooding the engine since new as well. One thing I have found out the hard way is some hose runs are critical to the inch and it doesn't take a lot to put a new hose "almost in the same place" and cause a problem you did not have before.
That long exhaust hose run to the stern would be one such run. The high section running aft will do fine with a slight slope going down as it goes aft and if rearranged to have the aft end slightly higher will send a lot of water running back to the water lock. This could make a hard-to-start engine much more prone to flood. I would check this run and make sure it has not gotten loose or moved in such a way that would encourage flooding. IMHO

[ndutton]

The volume of the waterlift should be able to contain all of the normal exhaust hose backwash. The Pearson exhaust system is configured exactly like the Catalina 30 with a couple of significant differences:

1. The Pearson has its engine under the cockpit, the Catalina under the dinette meaning the exhaust hose is nearly twice as long and therefore risks a much greater backwash volume.
2. The Catalina has far less hot section rise than the Pearson or just about any other boat model on this forum, like maybe 4 inches.

If the Catalina exhaust system can work reliably (I've never had a water incursion) then the observations of the Pearson exhaust should not raise concerns. As for the reports of wakes/following seas finding their way up the exhaust and overwhelming the waterlift, my Catalina has an exhaust thru-hull external flopper and a stainless check valve at the high point of the exhaust hose. Never a problem.

I think we might be getting distracted from the issue in this thread. The engine ran fine as configured for 200 hours then all of a sudden it gets water in the oil without anything changing. Remember, testing has confirmed the water jacket is intact as is the manifold and the original topic of this thread, the head gasket. The exhaust has not been altered - - - YET.

[joe_db]

The other issue - running temps.
My FWC setup would routinely hit 200-210 degrees at high power settings in warm water. That is well under the boiling point of glycol mix with even a 3 or 5 PSI cap, but that much heat in the boat was annoying and it could cause vapor lock on long trips on a hot day.
I went back to RWC that easily holds under 140 to consider my next move, either a better FWC system, a vapor purge line, or both. I don't think your temps are too far out of line running max power in warm water.

[ndutton]

Joe, I went through that too. Prior to converting to FWC I gave her a good acid flush so my internal passages were as clear as they were going to get. I did not have a thermostat and closed the bypass (full cooling), replaced my raw water pump with a new MMI 502 flange pump which helped a little but what really made the difference was replacing the HX with a new one as big as I could fit in the space (SeaKamp from Mr. Cool). With it and the new MMI thermostat I can run hard at a controlled 170°~175° all day.