5.7 mercruiser has no oil pressure

[Si Rey]

My 1989 Sea Ray has a 5.7 merc with remote oil filter, fresh water cooling system.
Changed oil and installed a NAPA gold oil filter and Castrol 15/50 motor oil a couple of months ago. Went to the lake, engine started fine and ran fine. Next morning zero oil pressure - but no low oil pressure buzzer.
Checked oil level - good.
After running 3-5 min oil pressure comes alive. All was good the rest of the rest of the day. Next trip same thing. Replaced oil and filter with Sierra marine oil filter and Quicksilver marine oil, no problems good oil pressure.
Next couple of outings were uneventful.

This weekend engine started good oil pressure, next morning zero oil pressure for the first 3-5 minutes. I replaced oil sender when this problem first started but to no avail.
Surely an oil pump could not act like this? or could it..............?
It acts as if it is loosing its prime, but only in the morning after the engine sits overnight.
Oil pressure when it comes alive is 50 psi at idle, 65-70 @ w.o.t.
Is there a bypass valve for the remote oil filter assy? that could be faulty
Thank you in advance to those with input.

 

[Apollo75]

Re: 5.7 mercruiser has no oil pressure

Well, if the engine did not have oil pressure for 3-to-5 minutes it would clatter like hell --- I would imagine this is not the case ---> there may be a problem with the sending unit, gauge, or wiring.


OFM

 

[QC]

Re: 5.7 mercruiser has no oil pressure

but no low oil pressure buzzer.

There's your clue . . .

 

[jtybt]

Re: 5.7 mercruiser has no oil pressure

Put in a mechanical oil pressure gauge.

 

[JustJason]

Re: 5.7 mercruiser has no oil pressure

Put in a mechanical oil pressure gauge.

Ditto... double check it with a real gauge.

Either your oil pressure sender, or your gauge, or the wiring is lying to you... because the oil pressure switch hasn't been fooled yet.

 

[Si Rey]

Re: 5.7 mercruiser has no oil pressure

Thank you all for your response,
makes good sense on the mechanical gauge issue, will do that and see what happens. I did replace the sender when this first rear its ugly head (doesn't mean that that one is good also).
So, a hunting we will go - a hunting we will go - off to the Auto Zone a hunting we will go..............