Low compression one cylinder 5.7 GSi

[buddha98]

I have a 1998 Seaswirl with a Volvo Penta 5.7 GSi Model #57FCPBYC that used to go up to 65mph. It over-heated due to a bad pump impeller. Water got sucked into the engine as it cooled down. The dealer replaced the head gaskets and impeller within a day or two. The boat now only runs up to about 49 mph. There is no water in the oil and no smoke coming out of the exhaust. I checked all the plugs and they look clean. I did a compression check and found all cylinders at 196 to 199 lbs. of compression except for cylinder #2. This cylinder went up to 191 lbs., then dropped to about 170 lbs. after a few more revolutions. I put a little 30W oil into the cylinder and the pressure very briefly went to 191 lbs. and then jumped around between 170 to maybe 189 lbs. I also noticed a little water spritzing off the engine near cylinder 2 when I was warming the engine up. I am not sure if the water is squirting out of the water pump or at the head gasket, its hard to see.
Do you think I have a leaking head gasket, a sticking exhaust valve, or maybe both? I winterized the boat now, but I was wondering if it would be OK to put a little Marvel Mystery Oil in the engine to free a possibly sticky valve in the spring time.

 

[Don S]

Re: Low compression one cylinder 5.7 GSi

5.7 GSi Model #57FCPBYC

That's an OMC model number, not Volvo.

I would be pulling the risers off the manifold and checking the gasket surfaces. They tend to leak after an overheat.
I would also be checking my compression gauge. You shouldn't be seeing that high of compression .

 

[Bondo]

Re: Low compression one cylinder 5.7 GSi

Ayuh,.... Welcome Aboard,... If it went from 65 mph, to 50 mph,... How low is yer Wot rpms,..??

Ya lost 15 mph, Marvels ain't gonna cure that,... Something is Seriously Wrong...

'n I agree, yer compression gauge is wacked,.. 150/ 175 across the board is more likely...

 

[buddha98]

Re: Low compression one cylinder 5.7 GSi

Ayuh,.... Welcome Aboard,... If it went from 65 mph, to 50 mph,... How low is yer Wot rpms,..??

Ya lost 15 mph, Marvels ain't gonna cure that,... Something is Seriously Wrong...

'n I agree, yer compression gauge is wacked,.. 150/ 175 across the board is more likely...

Yeah, those sound like some good ideas. I will investigate it as thoroughly as my skills will allow in the spring. My

compression gauge looks like new and was only used a few times, but it is 25 to 30 years old ( I thought those readings

were really high too ). As for the part number, I bought the boat new in Sept. 1997 and the boat model year is a 1998,

but maybe the engine is considered a 1997? I think there was a transition around then from OMC Cobra to Volvo Penta.

The label on the valve cover had the part number with the OMC Cobra name, but everywhere else on the engine and

outdrive it says Volvo Penta.

I don't remember the exact RPM at WOT, but it is definitely lower than normal ( I think around 3400 RPM ) due to a lack

of power. I can barely get the boat on plane now. Everything else is in excellent shape ( prop, hull, etc. ). I also have

one other theory that I'm hoping is not so. It's possible that my compression is WAY lower than my faulty gauge is

showing due to cooked piston rings and/or scored cylinder walls.

 

[Don S]

Re: Low compression one cylinder 5.7 GSi

You can go to this link http://epc.brp.com/Index.aspx?lang=E&s1=1857e413-b669-4f83-a0a4-0a15197763f2&brands=ej you will find your model number in the 98 sterndrive section.
98 was also the last year for OMC Sterndrives. Volvo bought them out. Between 94 and 98, Volvo and OMC were in a joint venture, and they both sold basically the same thing.

For sure get another compression gauge and recheck the compression test, but with your WOT rpm so low, it could be a lot of things.
I made a list a long time ago, go through the list and verify (don't just assume) that everything is as it should be, and you will find the problem.
http://forums.iboats.com/showthread.php?t=295070

 

[Bondo]

Re: Low compression one cylinder 5.7 GSi

I don't remember the exact RPM at WOT, but it is definitely lower than normal ( I think around 3400 RPM ) due to a lack

of power. I can barely get the boat on plane now. Everything else is in excellent shape ( prop, hull, etc. ).

Ayuh,... Drop the fuel filter, 'n inspect it's contents for stuff other than gasoline,...
(ya, it's on Don's list)