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Oil Pressure Issues 37 Mercruiser

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rick0795

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"I have a 1988 3.7 I/O Mercrui

"I have a 1988 3.7 I/O Mercruiser. I just had the engine tuned and all fluids and filters changed. Ran the boat a few times (ran great). The other day I noticed the top end getting noisy. A good deal of knocking from the valve cover. I also noticed at very low RPM's my Oil pressure was between 5-10 PSI. When I throttled up, the oil pressure started to riser to approximately 40 PSI (Which is Mid-Range on the Gauge). When I push it to higher RPM's, the pressure starts to enter the 60-80 PSI Range. It doesn't seem to matter what the PSI is, there is still a lot of noise coming from the valve cover. (Rocker Arms) are ticking. Any ideas as to what could be causing this problem?

Thanks Rick."
 
""I also noticed at very l

""I also noticed at very low RPM's my Oil pressure was between 5-10 PSI."

The gauge or pressure sender may be off. Low end of oil pressure is 15 PSI at idle; your low end is borderline. As long as oil pressure is 30-60 PSI @ 2,000 RPMs it should be OK.

What weight oil did they put in the engine?"
 
I purchased the oil and filter

I purchased the oil and filter for the mechanic and took the information right out of the manual and double checked with the oil cover information. I also checked the oil level and it is perfect. The engine has been well maintained and has had frequent oil changes. The engine is 21 years old and the oil looks as if you took it straight from the can.
 
Rick R.
Put a mechanical gau

Rick R.
Put a mechanical gauge on the engine and get your true readings from it. Can you adjust your valves?
Bert
 
"Bert,
I am not sure if I c

"Bert,
I am not sure if I can adjust the valves or not. I am going to have to do a little investigative work in the O&M. I beleive the lifts are hydraulic which will make for easy adjustment.

Thanks, Rick."
 
"Use straight 30 wt under 75 F

"Use straight 30 wt under 75 F., 40 wt over 75 F. or stick w/Merc. 25W40 wt oil."
 
"I appreciate your help. Afte

"I appreciate your help. After I check the valve cover/ lifts etc..., I'll do another oil change and use your advice.

Thanks again, Rick."
 
"hey rick, I have a 488 mercru

"hey rick, I have a 488 mercruiser which is the same engine just mine is a 1984 but still a 3.7. anyway, I use like they said here straight 40wt in mine all year on the water. My gauge acts exactly like yours, little to none on the gauge at 6-700 rpms idling, as soon as it hits 1000rpms it is around 10 to 15 psi, then 40 to 60 lbs above 2000rpms, of course more so when the engine and oil are cold. It makes a little tick at low idle but no noise as soon as the rpms increase. I doubt the valves can be adjusted I would guess they use hydraulic lifters but might be wrong.

Something may have come loose, i have noticed my boat needs ample warm up time or it will backfire if you hammer the throttle when cold which is hard on upper valve train. Bends valves, pushrods, etc.......

I never goose my boat until it is good and warmed up. I am sure there is a cure for it but I hate to mess with it and screw up something else."
 
"Valves are not adjustable. Th

"Valves are not adjustable. The only way to adjust is to change push rod length. They are torqued into place.

If you have a bad ticking then maybe a bad push rod, bad rocker arm or lifter or worn cam shaft.

Pull valve cover and watch while running carefully and compare to others. any noticable difference should be visable."
 
Also make sure the knocking is

Also make sure the knocking is from the valve cover area.

These motors are notorious for #1 and #4 piston/rod issues!!!!
 
"oh dear, i hope i dont have p

"oh dear, i hope i dont have piston/rod issues with mine - what causes that to happen? Poor Design or something else?"
 
"Usually water intrusion due t

"Usually water intrusion due to manifold leakage into exhaust and back into cylinder.

This motor was on a extended warrenty by merc that lasted into the mid '90's due to this problem, just so you know."
 
"from sitting in the water or

"from sitting in the water or what, exhaust manifold or intake manifold

from the boat sitting in the water and the engine not running?

are there any things you can do for preventitive medicine?"
 
"There is nothing to be done..

"There is nothing to be done.......

It is normally the intake/exhaust manifold as they are all the same part. there is a incoming "fresh" water it could be salt water if in the ocean, that runs thru the regulator and then up into the exh/intake manifold and flows thru to the exhaust elbow to cool the exhaust.

That water causes corrosion and eventually eroads away the thin wall that seperates the engine exhaust cavity and the fresh water cavity.

Bad design and they new about it thus the extended warrenty several years after they stopped making that engine.

If you have no water in the oil then you should be OK.

If you use in salt water........get manifold pressure checked!!!"
 
"gotcha, thanks for the info,

"gotcha, thanks for the info, sounds like I should be okay my boat only spends about 5 to 10 days in the water per year. The rest of the time it's on the trailer in my shop.

I will definately watch for water instrusion."
 
"The first thing I would do is

"The first thing I would do is replace that oil filter, pronto. There was another thread on here about an oil filter that desintigrated and left pieces of paper filter lodged in his oil galleries. If all this started right after the oil change then I would suspect something in that area. Who knows how long the new oil filter has been sitting around in a damp warehouse before you bought it. They usually aren't wrapped in plastic like the fuel/water seperator filters are. Just a thought."
 
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