View Full Version : Normal Compression?

06-26-2007, 06:39 PM
just ran a compression test on my '87 prostar and just wanted to know what the normal range is? I did it mainly to see if they were all approx. the same...anyways heres what i got

#1 - 135
2 - 135
3 - 140
4 - 131
5 - 125
6 - 130
7 - 130
8 - 120

Any input would help, thanks


ps, it has a 351W in it

06-26-2007, 07:50 PM
The numbers aren't great but they aren't the worst I have seen. If you did the compression test with the motor cold, that may not be bad. Warm it up, remove all spark plugs and then re-check it. If this was done with it at normal operating temperature, I would recommend doing a cylinder leakdown test. Could just be a bunch of carbon deposits on the valves, too.

06-26-2007, 10:46 PM
I did it cold, whats normal when I do the test after warming up the engine?

06-26-2007, 11:59 PM
It should be about 150.

06-27-2007, 09:07 AM
If my boat is running 'good as far as I know' should I bother with a compression test? Will it give me information I can use to keep the boat running or repair something before catastrophic failure occurs?

06-28-2007, 02:03 PM
my engine is running fine too, i just wanted to see if everything was up to par, becuase its 20 years old. I'd recommend doing a compression test, takes about 15 minutes and the hardest part is just getting the plugs out. at the least it will reassure you that the boats still good!