Yet another oil question

[GT40]

I'll start by saying that I bought my boat used from a Malibu dealer & they originally told me to use 10-30w oil in it. Okay, so when it was time to change the oil I read the manual that came with it & it says that PCM recommends 40w in the GT40 engine, so that's what I used. I have noticed both before & after the oil change that after the boat is really good & warmed up, when you bring the boat back to idle, the oil pressure drops to around 20. Is this normal? Is it just the analog gauges? Should I check it with a manual oil pressure gauge & if so, how do I do that? I called the dealer to talk with them about it & the service tech said that he actually recommends 15-40w Pennzoil (the same that Indmar recommends for the Malibus). I don't want to take it to my local Nautique dealer - I don't trust them as far as I could throw them. The boat is a '99 with 370 hours on it.

[skinautique]

Keep using the 40w. The guage will fluctuate from 20-60 given the circumstances. I have also seen some of them up at 80 for a little bit and then come back down. You should be just fine. Go enjoy it!!

[wburg64]

Go to this site and read , it should shed some light from experts..
http://www.vtr.org/maintain/oil-overview.html

[NCH2oSki]

After reading most of that article and checking out the posted numbers I think I will continue to use Mobil 1 15w50. I change it every 50 hours or so anyway.

[tryan]

most roller setups don't like synthetics unless you have 250# of seat pressure at the valve. go with a regular dino oil.

[Searay]

I noticed in the manual that the 40W oil should be SG rated. Is this easy to find and/or necessary for the GT-40 engine?