6/71 Oil Pressure

[Freestyle]

Can someone explain why I get a higher oil pressure reading (electrical guages) when at the dock out of gear versus underway at the same rpm's?

Bruce
Freestyle
1976 43 DCMY
Tampa

 

[LENZ]

Can someone explain why I get a higher oil pressure reading (electrical guages) when at the dock out of gear versus underway at the same rpm's?

Bruce
Freestyle
1976 43 DCMY
Tampa

Usually after the motor really warms up, the oil will get a little thinner which will cause the oil pressure to drop a bit. I installed a mechanical oil pressure gauge down in the engine room for ea motor just to be on the safe side.

Lenz

 

[yachtsmanbill]

A slight fluctuation can be attributed to thrust bearing load as well.This may be negligable or as much as 5 lbs. DDs really only need 1 to 1.5 lbs oil pressure per 100 rpm. 1000rpm= 10-15 psi as a worst case scenario.Those numbers are usually at the overhaul stage! ws

 

[Will]

Electric gauges are notorious for inaccuracies and variations which may result from changes in DC electrical loads, state of battery charge and alternator output. Their value is that they usually read close to the same under under the same conditions. As an example, if your O.P normally reads around 40 psi after running for 1/2 hour at 1800 RPM then suddenly drops to 20 psi, you had better check into things. Mechanical gauges are the most accurate.
Will

 

[spartonboat1]

My 6-71N's with approx 2,200 hours runs indicate 60psi port, 45-60psi stbd. The port is original, while the stbd is rebuilt (mostly- I don't think it was 100% everything, esp. oil pump and press relief valve).

When started, both go to 60psi, idling at 1,100rpm for warm up- rpm recommended by earlier post. When warm at dock, will show 60psi port, 50psi stbd. Then go for a run and at cruise, anything from 1,400 to 2,200rpm will show usually 60psi port, 50psi stbd (may vary +/-5psi but on a steady basis).

The relief valve on 6-71N' are set for 50psi, so you should be able to achieve that at rpm's in teens and up. When hot after a run at 600rpm or so, I will show 15-20psi.

Now my trannies (MG-506), that's another story. Getting weak at 270 to under 300psi, but hold real steady. Supposed to be 300+ I believe.

So that's the story of my 1972 DD's, plus the official relief pressure.