Blow-by on 1988 Mercruiser makes engine stall

JohnCiccarelli · Jan 23, 2010

I am noticing a lot of blow-by going up the hoses to the carb. The blow-by looks like steam or water vapor and when I allow it to go into the carb the engine stalls. The motor is a 1988 Mercruiser 260. Both sides seem to have this blow-by. Any idea on what might be causing this. If I raise the RPM the blow-by is reduced significantly. The engine runs great at anything above an idle.

Any help would be greatly appreciated.

John

Bondo · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Any idea on what might be causing this.

Ayuh,... Do a Compression Test,...

Blow-by is usually caused by Bad rings allowing combustion pressures into the crankcase...

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

I had a marine mechanic look at it and he did not think that it was normal oil/gas blow-by. He thought that it was steam/water vapor. Will a compression test identify this?

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

It does happen when the engine is up to temp. I have only run it once due to the fact that the blow-by being sucked into to carb makes it stall. It is a 24' boat and is hard to dock when it stalls. I really do not dare take it out again until I can get it to idle. Should blow-by cause the engine to stall?

I will check the compression as soon as it warms up a little.

Bondo · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Should blow-by cause the engine to stall?

Ayuh,... If it's because the Rings are Shot,... It'll be a Major contributing factor...

Ill motors Stall....

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Well I checked two of the cylinders and they are low. #1 is 60 and #3 is 105. Does this mean that the rings are bad or could it be valve problems?

I bought this boat with this problem, but changing the oil has seemed to make it worse. I used 10w40 Mobile One. I went to the Mercruiser site and they now recommend 25w40. Might this be of some help?

The boat runs great other then idle problems. I would really like to use it for a season before I do a major overhaul. Is there a way to vent this blow-by instead of feeding it to the carb?

Any ideas would help

John

Bondo · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

I would really like to use it for a season before I do a major overhaul.

Ayuh,... with compression #s like those,... That barge ain't goin' Nowhere without repairs...

100psi is Barely acceptable...

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

If it is really wore out, why does it run so good above an idle? It powered my 24 foot Cruisers to 38 MPH at 4500 RPM without a sputter or any hesitation.

I am also having a problem with the manifold controlled choke. It does not seem to open up all of the way. I first thought that it was the cold weather, but I now think that there is a problem. Are there any adjustments on these?

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Thanks for all of the responses. If I can't run it without a major overhaul, I guess I will not be boating this year. I had a free slip lined up until May. The only catch was that I would need to have the boat in it by February.

Thanks again, John

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

I guess I did not understand. I thought that you were saying bad rings. That would mean pulling the motor. I guess I will test the other cylinders and go from there. If it is a head gasket or valve problems, I may have time to fix it.

solar7647 · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

JohnCiccarelli said:
I had a marine mechanic look at it and he did not think that it was normal oil/gas blow-by. He thought that it was steam/water vapor. Will a compression test identify this?

I would get a new mechanic.... as bond-o said it is prob is a bad piston ring...its looks like steam because it is allowing the exhaust to blow through the engine into the valve cover via the crank case and oil ports that feed your head with oil and then into to carb. If you feel the valve cover it will probly be hot as He**

, I mean a lot hotter then normal.

I had the same issue....and after an oil change it got really bad...if you pull the head see if you can move the piston heads side to side in the cylinder that will be a dead give away.....I was able to fix mine without pulling the motor but I have a lot of space in the engine area just had to do it upside down

Good luck

Bt Doctur · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

I have a V6 doing the same thing, turned out to be a broken exaust valve spring ,was sucking water back into the cylinder. that can be changed without removing the head.

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Here is the bottom line on compression. They are all over the place

#1 60 #2 152
#3 90 #4 0?
#5 105 #6 60
#7 105 #8 152

Where do I go from here? I hope that this means more to you then me.

John

mkast · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Time for an overhaul.

ziggy · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

seems to me that if ya wanna try and find out where the issue is prior to taking it apart, a cylinder leakdown test may be in order.
or
http://www.boatfix.com/merc/Bullet/97/97_25.pdf
maybe the last part of this link. the air test.

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

At this point is pulling the heads off going to tell me anything? Or do I need to pull it out and tear it down?

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Bubba1235 said:
Yes, by inspecting the heads/valves/springs/gaskets you can determine where the problem is and what sort of repairs are in order. However, with that said and looking at your numbers, I am guessing that 30+ year old engine is just plain tired and needs an overhaul/replacement.

If it were me, I'd get on the horn to Rapido Marine and order up a $1,200 - $1,400 marine long block with a full warranty.

30 Years is a little high More like 22. Is 1,200 - 1,400 really the price or is there shipping and core shipping involved. I Rebuild a lot of Jet Ski's and Short Blocks are never a good idea. I know that jet ski's are much simpler (2 Strokes), but when you deal with the freight and returning cores, the final cost is more like $2000. Parts are usually less then $500. That said I will look into Rapido Marine. Thanks for the heads up.

John

JohnCiccarelli · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Thanks again for all of the responses. I really did not think that I was going to dig in this deep, but I guess I will start tearing it down tomorrow morning.

I still have to ask this. How can this thing run this good if it is this broke? 4500 RPM and 38 MPH. What should expect when it is perfect? I still do not not get how it can run this good. I never even expected this boat to run 38 MPH.

John

captmello · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

You should have done a wet compression check on the bad cylinders to see if the compression jumps up. The cylinders at 152 are ok, the rest are not. If the wet test doesn't raise the compression then you could look at just having the heads done. If the compression does jump by adding oil than the rings are worn, but you'd need to check all of them. Rings don't wear to 0psi. It's more than a tired engine.

Maybe someone did a bad valve adjustment on the motor.

Bondo · Jan 23, 2010

Re: Blow-by on 1988 Mercruiser makes engine stall

Rings don't wear to 0psi. It's more than a tired engine.

Ayuh,... It probably is tired,...
But with the 0 compression, I'd pull the heads, before buyin' a new motor...

Blow-by on 1988 Mercruiser makes engine stall

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