Oil leak

[gerritm]

I need some help from the experts. Maybe someone has had the same problem or can give me an idea what to look for.

I have staggered 525's in my '05 -- 42 Fountain Ex. When we bought the boat both engines had bad #8 cylinders from detonation and the tops of the pistons were cooked. We had both engines rebuilt. After a short period of time we noticed a fine mist of oil on the starboard saddle tank and some oil floating on the water in the bilge. It seems to come and go and is worst when we run the boat hard at full rpms. If we run easy it doesn't seem to show up. It is directly across from the forward port engine. The mist isfrom the bilge to the bottom of the hatch and all over the saddle tank. My mechanic has gone over every connection, oil plug, distributor seal etc trying to find the leak. It has to be dropping on the driveshaft and getting slung or misting out of something. There are no obvious leaks. Any ideas what it could be?.

[Ted]

Is it even with the front or the rear of the engine?

[gerritm]

Is it even with the front or the rear of the engine?

It seems more towards the rear. The mist is concentrated at the back of the saddle tank. We have pulled off all the rear covers and even put dye in the oil but it is so dispersed the black light picks it up all over.

[Ted]

There are known issues with the rear main seal on 502 blocks misting oil under a load, I think some of it has to do with the loose clearances they run for better oiling and the crank deflecting slightly.

[gerritm]

There are known issues with the rear main seal on 502 blocks misting oil under a load, I think some of it has to do with the loose clearances they run for better oiling and the crank deflecting slightly.

Kind of had a feeling that was what the problem is. We eliminated most everything else. Hoping it was a little simpler. Any issues with it blowing out the seal and losing all oil pressure? Do you think it is something I can live with until I can pull the motor in the future? It has been going on for about a year and does not seem to be getting much worse.

[Chris]

The BBC design doesn't ventilate the crankcase very well. Bottom-end windage can cause excessive lower crankcase pressures that don't help these problems. I can't remember who makes it, but I've seen vent plates that bolt to the block in place of the fuel pump- they have an AN fitting in them that you can plumb to a tank.

[Ted]

I know several people that have run better than 100 hours like that, it doesn't seem to get worse and does not effect the seal as far as anyione can tell.

[Offshoredrillin]

when the motors were rebuilt, some time the seal will wear a small groove in the crank, there are 2 different seals if I remember correctly as well, you may have one that is a c.h. too big. if the crank was scored from running lean and heat you may find the problem there.

[gerritm]

The BBC design doesn't ventilate the crankcase very well. Bottom-end windage can cause excessive lower crankcase pressures that don't help these problems. I can't remember who makes it, but I've seen vent plates that bolt to the block in place of the fuel pump- they have an AN fitting in them that you can plumb to a tank.

Chris, I am not sure what you mean. Are these vents plates run to the cooling system or water intake? Do you think it is excessive crankcase pressure due to heat? It does semm to be worse now that the temp is up in the 90's.

[Tony]

Degrease and scrub the motor and bilge. Go to napa and buy a small bottle of engine oil dye and dump in, run the boat then check the bilge with a UV light in a dark room.

Ive used this method more than once to locate the source of leaks.

[Chris]

Chris, I am not sure what you mean. Are these vents plates run to the cooling system or water intake? Do you think it is excessive crankcase pressure due to heat? It does semm to be worse now that the temp is up in the 90's.

You get crankcase pressure due to windage and blowby. The vents allow this to vent out to the atmosphere. You can run them to a catch tank. Outside temp shopuldn't have anything to do with it. Typically not a problem until you get into big inches, blowers and high RPM. You may want to look at your existing ventilation to see if there are any issues or obstructions.

[ROGUE]

Degrease and scrub the motor and bilge. Go to napa and buy a small bottle of engine oil dye and dump in, run the boat then check the bilge with a UV light in a dark room.

Ive used this method more than once to locate the source of leaks.

Or, if you are using a synthetic oil, Fantastic cleaner will turn a bright purple when it hits any synthetic oil I have seen. T

[OldSchool]

I can run all day @ 4000 rpm's and the bilge will be spotless. A few good minutes above 5800 and it's a mess. Big cubic inch engines will spray a little oil out of the rear main seal when they get the snot run out of 'em.. at least mine do! They're coming up on 100 hours and they've both done it from the get go. I change the oil every 25 hours and I've never seen either engine be even 1/4 of a quart low.


It's amazing how much of a mess just a an ounce or two of oil can make!!!

[gerritm]

Degrease and scrub the motor and bilge. Go to napa and buy a small bottle of engine oil dye and dump in, run the boat then check the bilge with a UV light in a dark room.

Ive used this method more than once to locate the source of leaks.

We have done this a couple of times. The leak is a mist and it goes everywhere. There is no way to pinpoint one spot or leak. It looks like a light show in the engine compartment with the black light.

[gerritm]

I can run all day @ 4000 rpm's and the bilge will be spotless. A few good minutes above 5800 and it's a mess. Big cubic inch engines will spray a little oil out of the rear main seal when they get the snot run out of 'em.. at least mine do! They're coming up on 100 hours and they've both done it from the get go. I change the oil every 25 hours and I've never seen either engine be even 1/4 of a quart low.


It's amazing how much of a mess just a an ounce or two of oil can make!!!

This sounds just like my engine. Run it at 4K rpm and almost nothing. Run it hard like we did this weekend in our Topps poker run and the couple of ounces of oil make a big mess. I squirt down the bilge and engine compartment with Purple Power and spray it off to keep it clean. I feel better that only 1 engine does it. I put a quart in every couple of times out and change the oil every 25 hours or so.

[Blue Thunder]

Plug up all the crankcase openings and figure out a way to put compressed air in the crankcase. 15psi is good. Then listen for the leak and/or use soapy water solution to spray the soapy water around the area and look for bubbles. I found a pesky leak just today after having the engine out twice looking for this leak and everything looked perfect. It turns out it was a valve cover gasket that visually I have no idea why it would no seal. This was an elevated rpm thing too.

BT

[Geronimo36]

I can run all day @ 4000 rpm's and the bilge will be spotless. A few good minutes above 5800 and it's a mess. Big cubic inch engines will spray a little oil out of the rear main seal when they get the snot run out of 'em.. at least mine do! They're coming up on 100 hours and they've both done it from the get go. I change the oil every 25 hours and I've never seen either engine be even 1/4 of a quart low.


It's amazing how much of a mess just a an ounce or two of oil can make!!!

Mine do the same thing under boost.... My other buddie has the same issue.

Was thinking it was a JC thing but then realized you had yours re-done by MGD.

[OldSchool]

Was thinking it was a JC thing but then realized you had yours re-done by MGD.

One redone..One complete new engine.

[Ratickle]

Do you have a picture of your engines for the ventilation review? My 540's on the Scorpion are terrible at it, if I run with the breathers only, I have to wipe it up a lot.

[gerritm]

Plug up all the crankcase openings and figure out a way to put compressed air in the crankcase. 15psi is good. Then listen for the leak and/or use soapy water solution to spray the soapy water around the area and look for bubbles. I found a pesky leak just today after having the engine out twice looking for this leak and everything looked perfect. It turns out it was a valve cover gasket that visually I have no idea why it would no seal. This was an elevated rpm thing too.

BT

The leak is getting worse. When you say plug up the crankcase openings and put compressed air in, other than making sure the oil fill caps are on tight, what else do you plug? I can make a fitting to screw on to the dipstick/oil drain hose connection to add air. Is this going to work?