Oil pressure on 1986 OMC cobra 5.7

[ImSwim]

The impeller wasn't working the other day when I launched it, I didn't notice right away and the engine got extremely hot. I've since replaced the impeller/housing and some gaskets that were brittle because of overheating. I had the engine running on muffs today, just idling. The oil pressure/engine RPM values were as follows;

750 RPM - 15 PSI - 71°C/160°F
1000 RPM - 21 PSI - 71°C/160°F
2000 RPM - 32 PSI - 77°C/170°F
2500 RPM - 33.5 PSI - 76°C/168.8°F
3000 RPM - 40.5 PSI - 78°C/172.4°F

I'm worried that the engine overheating caused some damage. These oil pressures are a little low, no?

 

[itsathepete]

OIl pressure is a little low compared to a new engine but acceptable especially if the engine is original. 10 psi per 1000rpms for a small block is typically fine. Keep an eye on your oil. If it gets milky/cloudy you have water intrusion, likely due to a head gasket or exhaust gasket leak.

 

[kenny nunez]

The engine temperature even on the flushout should not go over 160*. You may have some water pump impeller parts blocking the cooling system.
Just be sure that the temperature stays @ 160 when you put the boat back in the water.

 

[Lou C]

Make sure you don't have impeller bits in your P/S cooler, thermostat housing and the hoses leading to the manifolds.
If your old impeller was not 100% intact I would:
Remove the impeller housing, disconnect the raw water intake hose at the thermostat housing, stick a garden hose in the raw water intake hose and back flush the hose check to see you have good flow out of one of the ports on the impeller mount
Remove the stat housing to check for any bits in there, remove manifold feed hoses to check for same.
Reinstall the impeller housing, when you run it on the water hose, leave the plastic cover off and look for leaks around the housing, this means the o ring gasket may have shifted out of place. Also make sure the little bleed fitting is open and water flows out.

Oil pressure?
well my old 4.3 suffered a bad overheat 9 years ago and and 3 years after that both head gaskets started leaking. Even with those 2 adverse events my oil pressure did not change from what it was before...
Cold idle pressure 40, running at speed 40-60
hot oil pressure after coming off plane @ 600 rpm lowest it ever gets is 20, bumping up the idle it jumps right back up to 40.
This is running Merc 25/40 conventional oil.
I would not use 5w- or 10W- anything in these engines, only straight 30, 40, 20/50 or the Merc 25/40. Auto spec multi vis oils will thin out under marine engine duty cycles.