Logo
FULL SITE MENU

Mercruiser 4.3lx issue

J

Jonny_little

New member
I have a 93 18' northwood with a Mercruiser 4.3lx, alpha 1 outdrive open cooling system. I bought this boat cheap knowing it had issues. It gets water in the oil, but only when its in the lake. I can run it in my backyard all day with the hose and I can't find any water in it. I've heard cracked block/intake, head gasket/intake gasket, or cracked exhaust manifolds. The exhaust manifolds and risers are new, so I don't think that's the problem. Being that it only happens in the lake, could it be the exhaust flapper is going bad? I don't hear any clanking or anything, just that the gimbal bearing is bad. Any input is appreciated.
 
could it be the exhaust flapper is going bad?
Click to expand...
It would hydro lock if water rushed in thru them. They are easy to check. Is there water in the cylinders? Pull the thermostat out and poke around the bottom area of the intake manifold w/a pointed screwdriver or awl...you are looking for rust thru.
 
Your intake is probably bad. When in the water the pump in the lower can deliver full pressure and flow to the engine. The hose cannot supply enough. Remove your thermostat housing and look for a hole in the cross over tube in the intake.
 
Docksidemarineservices said:
Your intake is probably bad. When in the water the pump in the lower can deliver full pressure and flow to the engine. The hose cannot supply enough. Remove your thermostat housing and look for a hole in the cross over tube in the intake.
Click to expand...
Thanks for the input. I checked the flappers and they both looked good. I'm off to college now so it'll be a while before I get back to poke around some more. Thanks again.
 
I hope you have drained the water/oil out and refilled w/fresh oil. Also pull the spark plugs and give each cylinder a dose of oil and crank the engine a few turns. If you don't it may be rusted and seized when you return to it.
 
Yeah I drained it twice, ran fresh oil and a new filter both times. I work at Napa so I get stuff cheap. ;) I'm just new to the boat world. But, there's no more water in the oil as far as I can see. I'll have my dad run it a few times while I'm gone just to be sure.
 
Well I checked the intake manifold at the thermostat housing and it was rusty, but definitely not rusted through. There was still plenty of manifold there. I checked the heat riser bolts and they seemed a little under-torqued on the left side. One bolt was around 15 ft.lbs and the rest were about 25. The right side bolts were all around 40ft.lbs. I'm thinking that could have been the problem, but I'm not certain. Does anyone else have other ideas? Thanks, Jonny
 
I did a pressure test on the block(bypassed the manifolds and risers) and saw that I would loose about 1psi a minute. So I was sure that there is a crack somewhere. Until I checked my plugs in the hoses and saw that there was air coming through the grain of the wood.(go figure) I didn't have time to make new plugs before I had to leave for college again. My question is that if there was a crack in the block or a blown gasket, would the leak be more substantial than that? I know I don't really have an accurate reading. I'll have to use better plugs when I go home next weekend to know for sure.
 
External cracks from freezing can be big. Hairline cracks in the block sometimes can only be seen by magnafluxing w/powdered iron. However, if the water is leaking from the water jacket there should be a rust trail. What did the exhaust shutters look like? If they are not working that could be why you only get water in the oil when on the water...backwash runs into the exhaust valves. But, that tends to cause hydro lock. Open the oil fill cap and listen for hissing when pressurized.
 
I check the exhaust shutters and they both looked good. As for cracks on the outside, I couldn't find any. I sprayed the whole block with soapy water. There is a rust spot on the top of the intake manifold but I didn't see any bubbles with the soapy water. I'll make better plugs this weekend and give the pressure test another shot. I'll pull all the spark plugs and see if I can hear anything hissing there along with the oil fill cap. Thanks, Jonny
 
Back
Top