GM 4.3 Water in Oil Question - Boat Content: Grassroots Motorsports forum: Grassroots Motorsports Magazine

Subscribe get a full year for only $23.95 Sample Free Test Drive—no strings attached

April 26, 2010 11:38 a.m. VWguyBruce HalfDork

Bought a used boat from a coworker at the end of last season and finally got it running right and running well. As a result, I started replacing all the fluids in preparation of this years boating season. Prior to buying the boat the dipstick only showed black oil, nothing creamy and milky like water contamination. So, as I'm pumping the oil out the other day the first few pumps are water. Naturally, I assume the worst and consider my options. Just to make sure the water IS seeping in from a head gasket I change the oil and filter then let it run for nearly an hour with the water pumping through the entire time. I figured this was a cheap, easy way to verify something was or wasn't wrong.

Results were promising. Clean oil samples at 30 minute intervals with no evidence of oil contamination. I'm going to let it sit a couple days and take another sample to verify that the head gasket isn't at fault. After that I'll change the oil again to get any remaining water out of the system from before.

Boat history. PO was not a boat person. Boat has been sitting in his driveway covered for the last two years. Previous to that it was in the water for an entire season. Before that I don't know. PO doesn't remember anything about service on the boat except for me to ask the marina where he took it when it didn't start.

Would you guys call the motor good with what I'm doing or would you guys change head gaskets to make sure they aren't to blame? Anything else you'd recommend I do?
April 26, 2010 11:53 a.m. Woody SuperDork

Boat engines tend to have few hours on them, but deplorable maintenance histories. Especially V-8's. Especially x2 when they have twin V-8's.

If the oil comes up clean, I'd do a compression test and if the numbers are good, you're probably good to go.

Get a membership with Sea Tow or a similar service (AAA for boats) before going out too far in any boat, though. If you need them once, the savings will pay for several years in membership fees.
April 26, 2010 11:57 a.m. devina New Reader

I think you are on the right track. If you are in a northern climate, not getting all the water out of the block before winter could have cracked the block somewhere but that usually cracks the water jacket to the outside of the block, if memory serves.
April 26, 2010 12:15 p.m. tuna55 HalfDork

I wonder if it's possible that water got in from the outside via weather and never mixed with the oil, just sat on the bottom?
April 26, 2010 12:32 p.m. John Brown SuperDork

I think fishydoublenickels may have it.
April 26, 2010 12:45 p.m. hamburglar New Reader

How cold do winters get for you? Frost plugs should be on the bottom of the block, both sides and under the exhaust manifolds. For a 4.3 GM there are 6 plugs if memory serves. What year is it? and mercruiser or volvo?

If you are really suspicious of a cracking, the likely place on your block would be right underneath the head, which may explain your oil in water... It's not too bad though, you can get a reconditioned engine for about 1750$

Personally, I would check compression first, then run it for half hour, check for oil in water (you may need to let the oil settle...). If you don't have any water then I wouldn't worry to much...
April 26, 2010 5:19 p.m. VWguyBruce HalfDork

Thanks guys.

It's a Mercruiser 4.3LX. It's only got 235 hours since new in 1997 which of course can be a problem with boats, lack of use. I'll do a compression check tomorrow after I check for water again.

I'd say it only gets to mid to high 20's during the winter. Winter did get nasty here this year before I could get the fuel pump changed and winterize it.

No cracks visible in the exhaust manifolds or risers. I do intend to pull the riser on the right hand head as it runs a bit hotter than the left head and flows a bit less water. Temps still never get over 160 running it around 2500 rpm, I can still put my hand on the riser.

When I finally put insurance on it with Boat US they have a tow service add-on that cost next to nothing when it comes to a $250 tow. I'll never go another season without it.
April 26, 2010 9:11 p.m. Toyman01 Dork

MerCruiser manifolds are notoriously thin castings. When they fail it drizzles water back in the cylinders and if lucky past the rings and into the crankcase. I would pull them and have them pressure tested. They won't drain water in to the crankcase until you shut it off. If you are running salt water I would change them unless they are fairly new. On raw (salt) water cooled engines I would change them every three years, bad or not. On fresh water engines I think they recommend pressure testing every five. I would suspect the manifolds before I suspected the engine unless it froze. Frozen engines usually piss water outside the block though.

If it is the manifolds, be careful with the starter next time you crank it. Water doesn't compress and bent rods suck .
April 26, 2010 9:12 p.m. Toyman01 Dork

If you end up replacing the manifolds, get the GLM ones. They are galvanized and use a better casting than MerCruiser.