Low Oil Pressure when surfing...

[blackout00]

Hope everyone is doing well. Just wanted to ask a couple of questions in regards to oil pressure for anyone that is surfing on the older Supras. Here is what I have noticed...

1. When I start the boat up I have normal oil pressure.
2. The oil pressure when cruising stays normal.
3. Once we begin to ski, surf, or skate, the oil pressure gets very low.
4. The boat has plenty of oil on the dipstick when cold and when I check it on the water after being run
5. Water temp is always perfect. Never gets to hot.
6. Engine has no signs of oil starvation or not is making any sounds.
7. Boat has the 351 PCM engine

Overall I am curious if this is normal, if not what may need replaced, I do not know if this has been going on long. Thanks for all your help!

[cadunkle]

Quantify low... What RPM and what oil PSI? Good rule of thumb is at least 10 psi per 1000 RPM.

[blackout00]

I would say about 10 PSI when surfing at about 2200-2500 RPMS. The gauge did at one point go to just above 0 but again, no other change in behavior from the boat and it was at normal pressure when the day started...Not sure what is up...Thanks!

[blackout00]

What all could I check? Do I have a sensor that I can check? Wires? Could it be the gauge? Any help is appreciated...Thanks!

[wotan2525]

I think an auto parts store should have a handheld mechanical gauge that you could rent or buy. I'd try to hook one up to see if the oil pressure is actually low, or if the sender is just indicating low. The sender is based on resistance so it is possible that it could go bad (though I've not seen that happen before on this board.) Once you figure out if the oil pressure is actually low or only indicating low, you can go from there. I'd replace the sender before the gauge.

[cadunkle]

Yep, check with a mechanical gauge first just to be sure pressure is actually low 10 PSI is way low to be surfing at. What pressure at that same 2200-2500 RPM in neutral? What about at 3000 RPM or whatever running on plane?

Sounds to me like you're probably due for a rebuild. How many hours on the engine? How was the oil when you changed it? Clean? Dark/thick? Any metal in it?

One easy thing it could be is lack of oil in the pan which could be caused by plugged drainback holes in the heads. If pressure starts higher but quickly drops, pull the valve covers and ensure your drainback holes aren't plugged with gunk or parts of deterorated valve seals. There will be one hole at the front and back of each head.

Likely though, you have worn main and rod bearings with excessive clearance and it's just time for a freshening up. Other things could be a clogged pickup screen, cracked pickup tube, damaged oil pump, etc. If it's any of those things though you'll have to pull the engine and at that point you may as well at least pull it apart, check clearances, taper, etc. and either do a cheap freshening up with new rings and bearings or if there is too much taper in the bores just rebuild it.

[blackout00]

Thank you for all the responses. The motor only has about 775 hours on it. The engine shows no signs of need of rebuild as the oil is clean, motor is not burning any oil. I will def check the drainback holes as well as I did have the valve seals were just replaced in the spring. Stay tuned, and any other input is surely welcomed...

[beast 496]

What weight of oil are you using? I remember a few years ago a guy brought his boat in for service quoting the same thing. Just after he changed his own oil. He had put in 5W30 rather than 15W40 or 20W50 or even straight 30w. We changed the oil cut open the old filter, no problems after inspection. The engine is still running strong. I have a customer with a PCM GT 40 with over 1800 hrs no problems at all

[rludtke]

What weight of oil are you using? I remember a few years ago a guy brought his boat in for service quoting the same thing. Just after he changed his own oil. He had put in 5W30 rather than 15W40 or 20W50 or even straight 30w. We changed the oil cut open the old filter, no problems after inspection. The engine is still running strong. I have a customer with a PCM GT 40 with over 1800 hrs no problems at all

I have always been a little mistrustful of these modern multi-grade oils. It's hard for me to fathom how a 5 weight oil will actually behave and protect like a 30 weight oil.

Blackout, I'm with Al, try changing your oil to something of greater viscosity and see how it works.

[blackout00]

Hey Everyone -

I did some testing this weekend and I think the sensor is bad in the block. The sender is working and the gauge is working. Again, ran it this weekend with no problems. I will also change the oil weight. Thanks again for everyone's help! How much will a new sensor cost?