1996 5.7 Mercruiser Compression Test Help

Looking at buying a boat that is having troubles with a Startboard side motors. Both motors were replaced 3-4 years ago for long blocks and have less than 10 hours on them

The Starboard motor doesn't good so I decide to take a compression test. I found the numbers to be way off from my race car days some 25 years ago..but after reading here I'm not quite sure.

2 and three show quite a bit different than the rest but after reading here seem to be in tolerance. They are on opposite side of the motor so it doesn't
seem like it could be a riser issue...or a head gasket getting reading to check out.

Whatcha think?

1996 5.7 Carbureted

1. 190
2. 166 (checked x3)
3. 168 (checked x 3)
4. 190
5, 188
6. 188
7. 190
8. 188

Ayuh,..... Either yer gauge tends to read high, or there's water/ oil in the cylinders,......

'bout 150 psi is a brand new motor,.....
100 psi is rebuild time,.....

bondo said:

Ayuh,..... Either yer gauge tends to read high, or there's water/ oil in the cylinders,......

'bout 150 psi is a brand new motor,.....
100 psi is rebuild time,.....

Click to expand...

I guess it's possible the gauged was bad. I bought it today for testing so it was new. Plugs didn't look wet or oil foiled. In fact they look pretty good

out of the four plugs shown, the two in the middle appear to be running lean compared to the outer pair....assuming they all have the same run time accumulation...