Volvo 570a low compression in 3 cylinders

[Mariah1993]

Hi all,

I bought a used boat recently that has been nothing but trouble. It’s a 1993 Mariah 2200zc with a Volvo Penta 570 engine. It’s been running poorly since I’ve owned it so I finally did a compression test. Cylinders 1, 2, 4, 6, and 8 were all around 200 psi but cylinders 3, 5, and 7 were WAY too low; between 10 and 30 psi each. These 3 cylinders are side by side by side so I’m thinking that it’s either a blown head gasket or *gulp* a cracked engine block. Supposedly the block was replaced a year or two ago. I don’t know if that bodes well or if that is a red flag seeing that they may have been in a used engine block. Any other problems you think it could be that would cause near zero compression in 3 cylinders? Open to any suggestions!

Many thanks

 

[Scott Danforth]

first, welcome aboard

second, any cylinder over 150 means you have a bad gauge or there is either water or oil in the cylinders. at 200 psi, there would be enough water in the cylinders to squirt out as you cranked it, so I will assume bad gauge.

Third, is this a fresh water boat or a salt water boat? if salt water, you could have a leaking manifold to elbow gasket due to rust that is rusting your exhaust valves.

first thing you need to do is a leak-down test after your compression test.

then if you suspect a cracked block, do a pressure test of the cooling water jacket.

 

[QBhoy]

I’d ask if you have had water taken in through the valves at any point after a failed and worn manifold or riser. Making the valves stick open. Or worse, blowing the head gasket and causing this.
I’d also suggest your gauge is reading far too high. As far as I’m aware, these engines would never read more than about 160 psi give or take. Or you have more serious valve sticking issues.