4.3 leaking manifolds

So i just cant catch a break... I got another boat with a 89 4.3 merc in it and i noticed the manifolds leaking. I was told it didn't idle that good(sat for 2 years before this summer). I got it to idle nice, but when it warms up and idles for more then 20sec or so it starts to idle low and eventually die unless i give it a quick rev. im thinking its water from the manifolds being bad causing it to eventually leak down. if it was a head gasket it should idle rough all the time from all my experiences with blown head gaskets. also the oil got slighty milky after i ran it for prob 20mins(didnt noticed milky oil before and it was run at a local lake with the oil in it). The motor fires right up and runs awesome.

is it possible the manifolds internally cracked can cause these symtoms or am i looking at some more serious motor tear down?

another question i have is the starter wont engage. it free spins 9 out of 10 times before it grabs and turns over. Is this just the solenoid?

Re: 4.3 leaking manifolds

is it possible the manifolds internally cracked can cause these symtoms or am i looking at some more serious motor tear down?

Click to expand...

Ayuh,... Pull the manifolds, 'n Look....

Re: 4.3 leaking manifolds

I think you have multiple problems. The exhaust manifolds are not going to let water into the oil pan directly. The water that gets into the pan will come from water in the cylinders or water in the water jacket which leaks through a crack or blown gasket. If the manifolds are leaking back into the exhaust the water can get leak through open exhaust valves and down though the rings, but this is a slow process.

The idle problem will likely be a vacuum leak that doesn't become apparent until the engine heats up. You say you got it idling nice, but really it isn't idling nice until it's idling nice with the choke completely open. A partially closed choke will mask a vacuum leak. Once it heats up and choke opens all the way. spray carb cleaner around the carb to see if the engine revs. Just spray "gently" so that the carb cleaner does get sucked into the carb though the venturis. This will help you pinpoint where the vacuum leak is.

The starter problem could certainly be the solenoid, depending on your starter. The majority of Chevy starters have the solenoid on the starter, and it is responsible for kicking the starter drive out to the flywheel as well as transferring the high amperage current to the starter motor. If you do not have to turn the engine over by hand to get the starter to engage (sign of a bad ring gear), then the possibilities are 1. Battery voltage low, starter solenoid bad, or starter drive bad (sometimes they will bind internally and not kick out even though the solenoid is trying to push it out). You'll probably have to pull it to bench test it.

Chris

Re: 4.3 leaking manifolds

The manifolds were definitely leaking into the exhaust. There were rust puddles at the bottom of the ports of the manifolds. Hopefully installing new manifolds fixes it and I dont have cracked head or blown gasket.

Can water get into combution chamber at idle if the manifold leak is bad enough amd cause the motor to start stumblimg? Choke is wide open and it still idles grear for 20 sec or so. Runs fine off idle

Re: 4.3 leaking manifolds

It couldn't leak that badly, not to get into the cylinders while the engine is running. If you got enough water in there eventually it could cut the idling engine off because it can't push the exhaust through the water, but now we are talking about a load of water, much more than a leak. Besides, as hot as it is in those cylinders when the engine is running, if water got in there you'd have cracked rings as soon as the water hit them. Once the engine is no longer running, the cylinders are fair game for the water. The only caveat here is that if you have a cam in that engine that has a high enough valve overlap, it could suck water back into the exhaust. This is high performance stuff though, not stock.

I'd chase the idle issue as a separate problem for now.

Chris

Re: 4.3 leaking manifolds

Except that this is not a stock engine -- this is a marine engine.

Marine engines do run some overlap and can pull water into the exhaust -- causing all sorts of trouble. This is why we have have risers on our exhaust systems in the first place -- we do not want to pull the water we are sitting on into our engines....

It is very possible for enough water to leak in through the exhaust at idle to kill the idle -- higher rpm's produce enough exhaust to blow the water back up the riser -- lower rpms do not.

Remember that even though the manifold is on the drain end of the system, the water is still pressurized (at least to some extent) until it dumps into the drive end of the riser...

Running it like this long enough will allow enough water to leak past the rings to pollute the oil...

That said, it is entirely possible that you have another leak somewhere else, but I'd replace the manifolds and risers (don't cheap out here -- if replacing the manifolds, do the risers too) and go from there...

Hope this helps

Re: 4.3 leaking manifolds

That milky oil leads me to think you may have a cracked block. You say the engine was sitting for two years. Are you in a region with freezing temps or are you in a hot area, such as down south? If you're in the north, where things freeze, and that engine wasn't prepped for freezing temps, you're looking at an engine replacement. Think about that before you buy manifolds. If your engine needs replacement, you might luck out on finding a good used engine complete with manifolds. If not, you're looking at a long block and manifolds. Is the boat worth the cost? You decide. Hy

Re: 4.3 leaking manifolds

I got the entire kit from sierra. Manifolds and risers. I got a starter on order so whem it comes ill bolt up eberything.

I live in so cal so no freezing. thats where it sat.

Only other thing it could be is intake manifold. Well that I can think of. Ill update when I get it running .