I'm running twin Mercruiser 496 Mag engines in my 302. What kind of oil and filters are people using in their big blocks? I am currently running AMS 10W-40, but am noticing lower oil pressure.
On my old 2008 496 Mag I ran 4-cycle 25W-40 as Merc recommended and didn't have any issues. I have the PDF manual for the 496... drop me note at rob@boatingsuite.com if you want me to email you a copy.
Volvo also recommends 25W40. My 8.1L runs about 45lbs of pressure at 3000 RPM. I use factory Volvo filters, and have had no issues.
Years ago - when we had 9 planets - we had a 165hp Mercruiser - straight 6. That engine was bullet proof. We had approximately 500 hours on it and I was driving it WOT for quite a while and it was very hot outside - 100F+. All of a sudden the oil light went on and I immediately shut the engine down - we let the engine cool - oil was full - restarted the engine and the oil light was still on. I took it to the marina thinking I blew the engine - come to find out the oil that we used since day 1 straight 30W Rotella had broken down - I was religious in changing the oil and filter - so it wasn't the lack of maintenance. The marina said that Mercury changed the viscosity to 25W-40 and this is what we should be running - We changed oil and the it ran without issue. We sold this boat when we purchased our Cobalt- I've been using the 25W-40 as specified within the owners manual - I figure the engineers know a heck a lot more than I what is best for the engine. We have 7.4MPI and per the owners manual - the engine - if run hard will use a little oil. Well this summer was the first time that we were able to really open this bad boy up for an extended period - and sure enough at the end of the day - at least 7 hours running it hard (it was on lake Michigan - which was like glass) - it used about 1/2 quart. We have a little north of 550 hours on the engine -
