Pennzoil 80-90 or Mercury 90
 

The title says it all what and why oil do you use on your Mercury?

The cheapest one that says API GL-5....Marine hypoid 90 or 80w90.
West Marine brand or Sierra tend to be the cheapest. Don't find hypoid 90 in auto stores anymore.

Skunkboat,did you ever use pennzoil 80-90 ? That's what I'm using but when I drain it it looks like the color of antifreeze, that light green, so I think I'm going back to quick silver 90 weight. What do you think?

gear lube? I've been using the sierra synthetic blend hi-performance with good results, I go thru about 150 gallons of it a year. Bel Ray is no more so I bought a years supply of it discounted, its what I'm using now.Its a little darker green than the Sierra and feels thicker. Bel ray used to make Mercruiser hi performance gear lube. I use Sierra GL-5 full synthetic for the Volvo drives, it holds up better than Volvo OEM gear lube

I've never seen gear oil come out light green like antifreeze.


usually its almost as blue as when it went in....maybe slightly grey-greener

Skunkboat I know,it goes in like a brownish color and comes out a greenish color, it's not milky it just doesn't look right to me. Somethings not right. I did a water pump and base change this weekend maybe the base was letting water in? It's not been changed since 1988 the base I'm talking about

You can still find Valvoline Hypoid 80-90w in most auto stores. I usually buy it from Walmart.

all the synthetic and semi synthetic gear lube is tinted green, Automotive and regular gear lube is brown tint. Add water to the green stuff and it comes out mint green

Spareparts it is like a mint green, I changed the base of the water impeller , and I don't think it's ever been changed since 1988 it looked a little funky to me and since I think I am getting water intrusion from the base is only because when I ran the motor I never put the prop below the water line only ran it with ear muffs, also did you ever clean your thermostats? I was thinking I could clean them by putting them in white viniger, what do you think?