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Blow By? 1980 350

We have a 1980 carver mariner 33 with twin 350 crusaders. The starboard motor we cannot figure out what is happening. The motor starts perfectly, idles and has a ton of power. Problem is at about 2200 rpm the valve cover feeder tubes shoot out a thick white steam or smoke. This kills the motor at any high speed.

We had a compression check done and all is good. We had a leak down test done and no major issues found. all were within acceptable parameters according to the mechanic. So nobody can answer what is happening with the motor.

We thought head gasket but that was ruled out since there are no signs of water in the fuel....

I AM STUMPED! We have been through 4 mechanics and thousands of dollars and still cannot run our boat more that 7-8 knots.

Anybody every seen anything like this?

Thanks

Dan
 
Re: Blow By?

You need to determine if the 'stuff' you are seeing is smoke or steam.

What do you spark plugs look like?

FWC'ed? if yes, pressure tested?
 
Re: Blow By?

You may have a crack in the intake manifold, the exhaust crossover. Shoots exhaust into the lifter valley area, and then out the tubes.
 
Re: Blow By?

It is a freshwater cooled. We do seem to lose coolant regularly Spark plugs looked healthy. I think it is steam Since there is no exhaust or smoke out of the actual exhaust.

How to distinguish between the two?
 
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Re: Blow By?

Steam should condense on a piece of glass or mirror. Then, the water will evaporate. Smoke may condense oil mist or other particulates, and not evap later.
 
Re: Blow By?

Actually, the steam will condense on anything if its temp is below the prevailing dewpoint. Also, if you have antifreeze in the fresh side and you suspect it is leaking, the 'steam' should have that 'sweet scent'.

smoke is usually 'dirty' - like Dave noted; full of particulates - some would describe the residue as gritty. Depends upon what caused it.
 
Re: Blow By?

What's the oil look like on the stick? If chocolate milkshake like, you hae a cracked block or head(s). Hope not.

Jeff
 
Re: Blow By?

Okay, Sorry for the delay... Rainy weather....

I went and extended the tube from the valve cover to a glass. Revved to about 3000 rpms and it shooting out steam The steam condensed a overr the sides of the glass, but no sweet smell like antifreeze. I let it run about 15 minutes and noticed a white greasy substance was also left in the bottom of the glass. It smelled like exhaust. Just a very small amount.

Definitely steam or combination of steam and exhaust.

Thanks for any ideas!!!

Dan
 
Re: Blow By?

I suppose we forgot to mention that exhaust also contains a fair amount of water/steam as well. So, this test is not so easy! If you were not using coolant, it would most likely be exhaust leaking into the crank. Like from that crack, I mentioned earlier. If you are also loosing coolant pretty quickly, then obviously heads/gasket or even block crack rises to the top of the suspect list. That tube also contains "normal" blowby, further complicating this. Even a good engine will have some hydrocarbon content there. So, it goes like this:
normal engine: a little water, a little "exhaust". intake crack: lots of exhaust. big coolant leak: a little exhaust, lots of steam. Was the engine exposed to subzero weather last season?
 
Re: Blow By?

No, we are in Fla.

Basically, oil looks good, No film in the valve covers. Leakdown and compression fine. Some coolant loss,not huge though, plugs look normal, Ton of steam shooting out valve covers and small milky deposit with water that settled. Water tasted salty and carbonish but was clear except for the milky creamy oily residue at the bottom of the glass. Does this help at all?

I was googling and saw a guy with very similar problem and he said it was a fuel pump leaking internally? Does that make any sense?
 
Re: Blow By?

Basically, oil looks good, ...Ton of steam shooting out valve covers

That is hard to understand. Rather sounds like the steam was somehow injected into the crankcase, rather than having liquid water boil off. THe oil level is not INCREASING? Are these 454's? How old is the oil cooler?

I was googling and saw a guy with very similar problem and he said it was a fuel pump leaking internally? Does that make any sense?

NOt to me. Gas in the oil doesn't make water. Plus this "steam" would smell like gas and the site tube should be full of gas. Is there a site tube?
 
Re: Blow By?

The fuel thing did not make sense to me either? I have not checked to see if oil is increasing. I will check that tomorrow.

350 5.7 motors
 
Re: Blow By?

The "sight tube" is the flexible tube connecting the fuel pump to carb. connects on either end via hose barbs. Its purpose is to route any fuel from a leaking fuel pump diaphragm to the carb to minimize any fuel leak. An auto fuel pump has a differnet design and will 'leak' into the crankcase - a bad situation!

What do you use for "coolant"?

have access to a radiator pressure tester?
 
Re: Blow By?

Go back to the autozone - they will loan/rent you a "radiator pressure tester". No adapter required. That will let you check the coolant side of your system - the heat exchanger/block/manifolds. If it doesn't have directions, those can be emailed.
 
Re: Blow By?

The fuel thing did not make sense to me either? I have not checked to see if oil is increasing. I will check that tomorrow.

350 5.7 motors
I Have To Wonder if You Could Have A Crack On The Top Of Your Block... 350 Chevy's Have Been Known To Around Number 5 Or 7 Cylinder........I Would Be Looking Around There If And When You Take The Head Off
 
Re: Blow By?

It is also possible that the exhaust cross over in the intake manifold has begun to leak into the crank case either from the intake gasket or the tube itself. If the engine is dying as a result, I would check this first. Steam will not choke the engine. Exhaust gasses will. Also a fuel pump leaking gas into the crank case will choke your engine, the gasoline vapors coming from the hot oil/gas mix will choke the carb through the breather tubes.
 
Re: Blow By?

you can also get a "block test kit" (NAPA sells them). That will "sniff" the coolant for exhaust gas and change color if it's there.

It's basically a rubber stopper with a glass vile that gets held into the radiator (heat exchanger) in place of the cap.

Bob
 
Re: Blow By?

PLEASE try the above test 'cause I'm dying to hear the result. I agree that it HAS to be a massive exhaust leak.

Jeff
 
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