6-71N Oil Pressure

[Freestyle]

My starboard engine (2,750 hours) is showing over 75 lbs of pressure when I run at 1500 rpm's. If I speed up to 1750 or slow down under 1200 it drops to the 40-60 range and holds with a little periodic upward creep.

It just started doing this after an oil change last week.

Any thoughts appreciated.

Bruce
Freestyle
1976 43 DCMY

 

[Genesis]

That's not good if its real. Is this on a mechanical gauge? Electrical ones are notorious for doing this sort of wierd stuff.

If its mechanical, the oil pressure relief valve in the oil pump may be sticking closed.

 

[Freestyle]

That's not good if its real. Is this on a mechanical gauge? Electrical ones are notorious for doing this sort of wierd stuff.

If its mechanical, the oil pressure relief valve in the oil pump may be sticking closed.

Original guages at both helm stations which I assume are electrical but tell me if I am wrong.

What would make a relief valve stick at just a small (albeit heavily used) range of rpm's?

 

[Genesis]

Well, with what you're describing the senders are electrical and its PROBABLY the sender - not the actual pressure.

I'd pull the sender and stick a mechanical gauge in the hole, then see what you've REALLY got.

As for what could make the valve stick, problems with it are very uncommon - but not unheard of. My bet, however, is that there's a range on the sender that is "open" in the wiper part of the sender's element, which is causing the gauge to read false high. A quite-common fault. Confirm with a mechanical gauge before doing anything more drastic.

 

[Freestyle]

It's probably not the best way to diagnose the problem. But Dad drove the boat for 2.5 hours apparently with the guage in question pegged. He thinks you can never have too much oil pressure.

If I really had that kind of pressure and the guage wasn't just acting up, wouldn't my engine be dead now?

Bruce

 

[spartonboat1]

The pressure relief valve is spec'd to lift off at 50 #'s, or so I understand. If running/reading at 75 #'s, its either an abnormal reading or a sticking valve. I am not aware of any need to exceed 50 #'s to any degree at speed. I have one 6-71 that will creep near 60, but both tend to stay at or near 50.

Certainly worth analyzing to validate the source of high reading, esp, to avoid blowing out a weak hose and suffering loss of lube...(that can't be good, he said).

 

[MikeP]

Yes, you can have too much oil pressure and it will blow oil filters apart. Short of that, excessive pressure contributes to oil burning and wastes HP turning the pump. If the relief valve is stuck, the pressure will go up with RPM and keep going up as long as the RPM rises. There is no value in engine oil pressure being any higher than it needs to be to ensure adequate oil flow. DD reduced the pressure relief for 8V71s to around 50PSI some years ago. The logbook on our boat (1980 53MY) from the early 1990's show Oil Pressures in both engines of a around 75-80 PSI. After the engines were rebuilt (new oil pumps) the pressure dropped to 50PSI per current specs.

But I'll bet the problem is the guage, as Karl suggested. It's really a good idea to put mechanical gauges in the engine area. I'd suggest at least having mechanical oil P and water temp gauges. A tranny pressure gauge is useful as well. Of course, you can go nuts and put all sorts of useful gauges there.

I installed a panel with those three gauges and an engine start button in each engine room. On the first start of the day I start the engines from there so I can see the Oil P come up on the mech gauge.