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1989 OMC 351w Oil Pressure

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phillipjf16

New member
Hello all,

I just put a replacement engine in my 1989 Seaswirl. The used 351w long block came out of a 1992 Ford Truck. All Marine gaskets and parts were then added to the block from the previous motor.

The truck engine had about 100k miles on it but it looked very fresh.

Presently, my electrical dash gauge is saying the oil pressure is around 40 psi at cold idle, and 15-20 psi at hot idle. When the engine is up to temp, the gauge reads around 35-40 psi at WOT, 4500 rpm.

I wanted to confirm the readings with a mechanical gauge and when I did that, the readings were 35 psi at hot idle, and 45-48 psi at WOT.

I'm currently using 6 quarts of Castrol 10w-40 oil and a Fram Oil filter.

There is also no noise from the valve train and no knocking at any engine speeds.

Are these pressure readings in the normal range? I'm just trying to make sure my engine is operating correctly.

Thanks!
 
phillipjf16 said:
35 psi at hot idle, and 45-48 psi at WOT.
Click to expand...

I'd say that's typical for a 100,000 miler, but 10W-40 has no business being in a boat. (except Volvo Pentas with engine oil coolers)

You want straight 30, 20W-50, or 25W40 in there or you'll hurt her.

nothing that starts with 10 in a boat unless you are in the Arctic ocean

Some run 15W-40 and get away with it, but with those miles, I'd go a bit thicker.
 
Last edited:
Thanks hystat,

I'm leaving for a crabbing trip tomorrow and I dont particularly feel like changing the oil out since I've done it about 1000 times since the previous engine had a cracked block. :)

My plan is to swap the fram filter with a motorcraft and put in a quart of Lucas.

Do you think that will tide me over for a while?

- Phil
 
lucas is useless, straight 30 weight and your good to go. I use fram, but please lets not get into oil filter brands and oil brand debate.
 
multi vis is not bad for boats.

the 20W50 and 25W40 I recommended are both multi-vis oils

the issue with 10W40 is that it is simply too thin and with the high oil temp of a marine engine, it will thin out enough to cause oil pressure to drop below a level that can maintain bearing clearances
 
went through the same thing with a omc webcraft 24 fter i ended up putting a new crank kit in it it was worth the 150.00 for crank and bearings my boat has probly 200,000 on motor hard to beleive still running great with good oil preasure 351 wind motor
 
Remember, boats are always running uphill. They need a heavy duty oil to keep them happy. Use good old 30w and your engine will thank you.
 
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