85 johnson 25 compression how much psi

[RWKellenberger]

I have around 100 psi in both cylinders. is it possible to have combustion gasses escaping into the area around piston sleeves under the head gasket and still have good compression? reason for question is i am having water circ. issues beyond the water pump and clogs in the system. mechanic told me that if i have an exhaust leak somewhere esp. from the head gasket, exhaust pressure can overcome water pressure and it will not pee. also what is the correct way to check psi? do you just bump it over or crank it a few revolutions?

 

[wilde1j]

Re: 85 johnson 25 compression how much psi

100 psig is fine. I crank for a few seconds with all plugs out. Head gasket is likely OK.

What exactly have you done to make sure nothing is blocked up? When was the water pump done? Are you positive about the pump housing/liner and wear plate condition? Sure the outlet grommet isn't crushed or folded over? Etc., etc.

 

[HighTrim]

Re: 85 johnson 25 compression how much psi

We are also assuming that you flushed AND back flushed the cooling circuit while the lu was down to ensure free flow? Is the flow affected at all speeds/rpms? Is there any flow at all or just weak?

 

[RWKellenberger]

Re: 85 johnson 25 compression how much psi

I have replaced the water pump assembly last year, took it apart recently and the wear plate and steel cup is fine, housin looked to be melted some but the cup was still in place with the opening in position. impeller was is fair consition i guess. it had no wear on it but there was some mild cracking on the midsection of the fins. I have a new assembly on order because of the melting and impeller issue. i am not positive that is the problem. the boat will pump at idle and full throttle against a piling but not underway at all above idle. maybe weak impeller cant suck enough water underway? everything worked fine last year. nothing under boat to make pump cavitate. new water intake screen, water jacket gasket thermostat and head gasket. did this all a couple of days ago and cleaned out about a spoonful of seashells under the water jacket. no other obstructions. crossing fingers new waterpump will be the fix.