major white smoke from rebuilt 5.7 merc magnum

arriva2450

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I bought a "rebuilt" 5.7 merc magnum recently for my boat. The engine came with the intake manifold off, so I was not able to run or test it from the seller.

My mechanic put on the manifold and accessories (ie. starter, alt, risers, etc) and we fired it up for the first time the other day. Seems to idle smooth and accelerate nice, but it is spewing out a you-know-what load of white smoke. Read that some rebuilt engines can do this to burn off greases and other oils used during rebuild, but when is it supposed to stop? Also read that it could be rings, head gasket, or simply the intake manifold gasket (ie. mechanic may not have put it on right, or maybe the rebuilt engine was done bad).

I ran it maybe 30 minutes the first time and it did seem to eventually slow down. Let it sit one day and upon firing seemed to smoke alot again. After maybe 5 minutes seemed to slow down, but then again started smokking real bad.

Is there any way to pin-point what the issue might be? How about if I look at the plugs - will that tell me anything? BTW - seems to have OK power (similar to the engine I replaced which was the same type). Being that this was one rebuilt I was hoping for more, but again it is on par with my previous one (which I cracked the block on from bad winterization).

Oh, one more question. On top of the carb I have a filter housing with two hoses - each hose attaches to one side of the the valve covers. What are these hoses for?? I ask because the hose attachment (that connects it to the valve cover) is broken on one side so basically the hose is free (not connect into the valve cover). There is tons of exhaust (white smoke) coming from this hose, especially when I hit the gas hard. Is this normal?

Any advice would be greatly appreciated.

Thanks
 

RogersJetboat454

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Re: major white smoke from rebuilt 5.7 merc magnum

Bad rings, valve guides, or valve seals = Blue lingering oil smoke. Kinda like 2 stroke smoke.

You say you have white smoke...
Is this white smoke coming from the outside of the engine, or the exhaust its self? Is the smoke kinda puffy and moist (like a hot steamy shower), or is it kinda stinky and lingering, almost like blue smoke?

If you pull the plugs, are they oily looking, tanish colored, black, or do they look like they were just pulled out of the package?

The two hoses coming from the valve cover to the flame arrestor are part of the PCV system that allows the engine to burn off the nasty crankcase gases. A little bit of white smoke out of these hoses (vaporized condensation), especially after a cold soak, or extended period of lay-up is normal. If it's constant (doesn't reduce, or go away), you may be getting water in the oil. How does your oil look? Milky? Level been rising, or staying the same? If you let the engine sit a long time, then crack the drain plug on the oil pan open a little, does any water drip out of the pan?

Pictures/video of offending smoke, plugs, and anything else related may help us help you. ;)
 

Bondo

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Re: major white smoke from rebuilt 5.7 merc magnum

Ayuh,.... Is the oil level stable,..?? Any Smells,..??
 

arriva2450

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Re: major white smoke from rebuilt 5.7 merc magnum

The smoke is coming from the exhaust (not the block or anything). Except for the smoke coming from the PCV system, but that is due to the hose not being connected yet to the valve. It did not look fluffy, but rather just white smoke kind of like a camp fire after all wood is burnt but it is still burning away. The smell is very 'exhausty' smelling (normal exhaust) - it is not sweet or anything odd, and it is white not black.

Ok, did some of the tests.

Checked the oil, and although it looks like fresh oil (which it should since it is new except for maybe 30 minutes of running), it is about twice past the 'full' marker?? Not sure if my mechanic overfilled it, or if it is a sign of trouble with water getting in. But again it is not milky or watery??

Next I pulled one of the plugs. It is very black on the conductor / top, and the sides (threads and bottom of threads) has fresh black oil (wet) on them.

So what does that mean??

BTW - the engine stopped running yesterday. We were testing it at full throttle for a minute but the smoke in the engine compartment got too much (due to the PCV hose thing) so we turned it off. Since then it just would not fire up. Turns over but just not firing at all. Being that it is the first run of the year and that the gas is last years, I tested the fuel filter and it was fine (all gas, no water). Fiddled with the shifter and shift kill switch which made no difference. I think I have no spark. Mechanic will be returning this weekend to check into it, but I don't think this is related to the white smoke. But your thoughts? FYI - we just put in a new coil and new wires - maybe the coil is defective and somehow failed after 20 minutes of running???

Thanks

BTW - yesterday when we were testing, we shut it off as tons of smoke was in the engine compartment due to the
 

Bondo

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Re: major white smoke from rebuilt 5.7 merc magnum

The smoke is coming from the exhaust (not the block or anything). Except for the smoke coming from the PCV system, but that is due to the hose not being connected yet to the valve. It did not look fluffy, but rather just white smoke kind of like a camp fire after all wood is burnt but it is still burning away. The smell is very 'exhausty' smelling (normal exhaust) - it is not sweet or anything odd, and it is white not black.

Ok, did some of the tests.

Checked the oil, and although it looks like fresh oil (which it should since it is new except for maybe 30 minutes of running), it is about twice past the 'full' marker?? Not sure if my mechanic overfilled it, or if it is a sign of trouble with water getting in. But again it is not milky or watery??

Next I pulled one of the plugs. It is very black on the conductor / top, and the sides (threads and bottom of threads) has fresh black oil (wet) on them.

So what does that mean??

BTW - the engine stopped running yesterday. We were testing it at full throttle for a minute but the smoke in the engine compartment got too much (due to the PCV hose thing) so we turned it off. Since then it just would not fire up. Turns over but just not firing at all. Being that it is the first run of the year and that the gas is last years, I tested the fuel filter and it was fine (all gas, no water). Fiddled with the shifter and shift kill switch which made no difference. I think I have no spark. Mechanic will be returning this weekend to check into it, but I don't think this is related to the white smoke. But your thoughts? FYI - we just put in a new coil and new wires - maybe the coil is defective and somehow failed after 20 minutes of running???

Thanks

BTW - yesterday when we were testing, we shut it off as tons of smoke was in the engine compartment due to the

Ayuh,... Don't run it,... drain the oil,.... That is Water.....

Something, is very, Very Wrong with that motor,...

Drain it, 'n do some pressure testin',.... start with the water jacket test...
 

arriva2450

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Re: major white smoke from rebuilt 5.7 merc magnum

My dilemma now is trying to figure out who messed up (other than me). Another words, is this definately due to a poor rebuild (from the guy I bought the engine from), or could it be due to my mechanic not putting the intake manifold, riser, and exhaust right? I bought the engine for $1100 and I owe my mechanic about the same for the engine swap and assembly. Not sure what to do? Any advice.

FYI - the guy I bought the engine from seemed very mechanically inclined, and quite financially well off. He had a 50k$ boat in the driveway, a 500k$ home, nice cars, and a bunch of project motorbikes - I had no reason to doubt him. He said the engine had 40 hours after the rebuild which was in his boat but he swapped it with a 454. I guess it is weird why the intake though was removed if it was rebuilt and running in his boat.

Any advice would be appreciated.

Thanks
 

Bondo

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Re: major white smoke from rebuilt 5.7 merc magnum

My dilemma now is trying to figure out who messed up (other than me). Another words, is this definately due to a poor rebuild (from the guy I bought the engine from), or could it be due to my mechanic not putting the intake manifold, riser, and exhaust right? I bought the engine for $1100 and I owe my mechanic about the same for the engine swap and assembly. Not sure what to do? Any advice.

FYI - the guy I bought the engine from seemed very mechanically inclined, and quite financially well off. He had a 50k$ boat in the driveway, a 500k$ home, nice cars, and a bunch of project motorbikes - I had no reason to doubt him. He said the engine had 40 hours after the rebuild which was in his boat but he swapped it with a 454. I guess it is weird why the intake though was removed if it was rebuilt and running in his boat.

Any advice would be appreciated.

Thanks

Ayuh,... It was probably a trick intake, 'n carb that he wanted to keep... Who knows,...

Ya figure out who screwed the pooch by Diagnosin' it,...

Drain the oil,....
Drain the water,...
Pressure test the coolin' jacket,....

Dependin' on what ya Hear,....
refill the oil, 'n do a compression, 'n leak down test...
 

arriva2450

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Messages
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Re: major white smoke from rebuilt 5.7 merc magnum

Actually, it came with the manifold, just that it was off. Though no carb, starter, risers (but did have the exhaust manifolds).

Another question. My mechanic told me that the manifold was different from my old one, in that the manifold that 2 sets of 4 bolts for attaching the carb (almost like it was designed to allow different makes/models of carbs). To make my carb fit, he was able to use one of the sets of 4 threaded holes, but he had to fabricate a gasket.

Could that have any impact if the gasket connecting the carb to the intake not be good?

So just curious, could the problems I have be possibly due to my mechanic doing a bad job with the intake, carb, or exhaust manifolds, or is it definately internal (meaning I got screwed from the guy I bought the engine from)?

Just want to know if I should hold back payment to my mechanic until this is all tested, if there is a chance he messed up?????

Thanks
 
Last edited:

Bondo

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Re: major white smoke from rebuilt 5.7 merc magnum

Actually, it came with the manifold, just that it was off. Though no carb, starter, risers (but did have the exhaust manifolds).

Another question. My mechanic told me that the manifold was different from my old one, in that the manifold that 2 sets of 4 bolts for attaching the carb (almost like it was designed to allow different makes/models of carbs). To make my carb fit, he was able to use one of the sets of 4 threaded holes, but he had to fabricate a gasket.

Could that have any impact if the gasket connecting the carb to the intake not be good?

So just curious, could the problems I have be possibly due to my mechanic doing a bad job with the intake, carb, or exhaust manifolds, or is it definately internal (meaning I got screwed from the guy I bought the engine from)?

Just want to know if I should hold back payment to my mechanic until this is all tested, if there is a chance he messed up?????

Thanks

Ayuh,... This is a Diy site,.... I don't care who's Fault it is,.... We'll just tell ya how to fix it.....
 

RogersJetboat454

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Jul 9, 2010
Messages
2,964
Re: major white smoke from rebuilt 5.7 merc magnum

Actually, it came with the manifold, just that it was off. Though no carb, starter, risers (but did have the exhaust manifolds).

Another question. My mechanic told me that the manifold was different from my old one, in that the manifold that 2 sets of 4 bolts for attaching the carb (almost like it was designed to allow different makes/models of carbs). To make my carb fit, he was able to use one of the sets of 4 threaded holes, but he had to fabricate a gasket.

Could that have any impact if the gasket connecting the carb to the intake not be good?

So just curious, could the problems I have be possibly due to my mechanic doing a bad job with the intake, carb, or exhaust manifolds, or is it definately internal (meaning I got screwed from the guy I bought the engine from)?

Just want to know if I should hold back payment to my mechanic until this is all tested, if there is a chance he messed up?????

Thanks

How the carb is attached isn't gunna make one lick of difference to getting water in the oil.

Do the testing Bondo suggested, and you can make up your mind who you want to do the finger pointing at.

BTW, revving an unloaded engine to WOT NEVER helped anybody diagnose anything. Stop doing that before you send a rod through the side of the block...
 
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