I changed the oil in my starboard 502/415 engine yesterday and lost oil pressure and increased oil temperature. I was expecting just the opposite. I had been using Mercury 25W40 and a Mercury filter. I changed to Mobil 1 V-Twin 20W50 and a Mobil 1-111 filter. My oil pressure at idle went from 45 lbs. to 39 lbs.. My oil temperature, with the mercury oil, never left the peg until I got on plane. When I started the starboard engine and ran it for maybe 5 minutes, the oil temp needle started to move up. My question is, has anyone else experienced the same result as I did? I am going out for a run today and I will be watching the gauges. I am not changing the oil in the port motor until I am sure everything is OK.

I have tried the mobil 1 filter and I had a oil pressure drop in the boat and the truck. I have never tried v-twin oil. I would try your stock merc filter or a high flow filter like a K&N and see if the pressure comes back. The valvoline synthetic oil additive that was talked about on another thread will give you more oil pressure. I tried it twice and it worked both times.

Oil pressure is created when the positive displacement oil pump sucks up oil from the pan and pushes it through the filter into the engine’s main oil gallery. The oil is then routed to where it is needed: the main bearings, rod bearings, cam bearings, upper valvetrain and timing chain or tensioner. The oil’s viscosity makes it thick and slows the flow as it passes through the passages and bearings despite same output. The amount of pressure created thus depends on the oil’s viscosity. Heavier viscosity equals more pressure.

This wouldn't be the first time I've heard of an M1 filter gone bad. Change the filter to something other than an M1.

Sorry Hydro, but I am begining the think the M1 filters just don't live up to their spec sheets.

How many hours on on the engines? He went from conventional to synthetic...that is important to know!

I just switched. Pressure is the same at idle but does not increase much with rpms. I have an oversized cooler and my temp does not go over 140. I also use the Fram HP4 filter.

The HP4 flows good but is a near 20 micron filter.

Bob's Site on oil filters:

"NAPA Gold is a fine filter, seems to be well constructed and few complaints are registered here. Mobil 1 is possibly the best spin on filter you can get but you have to pay for it".

The additive also increases viscosity and that increases oil pressure.

Less than 10, they were just built. He didn't switch oils, just the filter