Big block losing oil into water jacket?

[John B]

This is a tough one! One of two Gen 5 crate motors 1994's is losing one quart of oil ever two running hours. It is not in the bilge and not apparently burning oil. The oil cooler was just leak tested on both sides, no leakage.

Is there any way oil can get into the cooling water and dumped overboard? Has anyone got any ideas? The problem has been getting worse over time.

Thanks for any suggestions. John B

[mmwalters]

John I would bet it is burning oil and you just can't tell. Remember 99% of the time it is just the basics!


One another idea, I am working on some transom water pickups on the lines of the NACCA scoops. I will let you know how my progress goes. Have you tested you modified water pickups yet?

[Doug]

He nailed it right on the head, do a leak down test. How many hours are on the motors? If your rings are starting to go away you will start to get some fuel contamination in your oil, thinning it out and burning more. May be time for a rebuild.

[John B]

The motors have over 400 hours. One is normal consumption, the other is using 10 times as much. I have watched and followed this boat while running and have not seen any oil smoke. Usually this much oil burning would require a pollution permit!

The owner and his shop are going to do a comp, and leakdown test. But you should see an oil cloud burning this much!

Michael, It is in the 40's up here. If I did test the 30 degree temp difference from the last test would not give us good data. Thirty degrees is about a 3% horsepower increase. I may wait until next spring. The latest changes will help, the question is how much. My guess is .5 mph, 10-15 lbs less water pressure and 100-200 less rpm at the same speed.

Thanks for the responses, John B

[Cord]

I once had a cracked cylinder head that let oil into the coolant. That was a holy mess to purge.

[John B]

Where was it cracked? I did not think there was oil under pressure in the head.

[Vinny P]

There is no pressurized oil in the heads. I can see water getting into the oil from the cylinder heads, but not the other way around.

[Cord]

Your right. I was just thinking of the situation and forgot about the application. That cracked head wasn't on a big block chevy. That engine did have pressurized oil feeding the valvetrain.

I guess the only thing we can get from my comment is the fact that the fluids are going to transfer from a high pressure to a lower pressure. If there is a crack passing through a oil galley and a coolant passage, then the oil will transfer from the high pressure galley into the low pressure coolant passage. I guess what I was really trying to say that it is possible for a crack to cause the oil to transfer to the coolant. It's a long shot, but it is possible.

[Steet]

The lifter galley is not under pressure if the engine has a pvc system. Otherwise, it is under some pressure.

[John B]

Well, it looks like the valves are flopping around in the guides!

There was no smoke at slow speeds!

Leakdown test = less than 10% with 400 hours.

Cam lift is around .560 with stock (crate motor) valve guides. The other duplicate motor is not having a problem yet?

Anybody know what would cause the guides to (go away)?