[moondance100]

I put a new (not rebuilt) GM 502 in my boat this spring. Thinking I'd use the heaviest most expensive oil I could find, I started off using 20w50 Mobil 1 and a K&N filter. The dang thing used oil from the git go. After about 30 hours of use, I had added about 6-8 quarts of oil (I lost count!) I was pretty worried. The engine ran great but my old 350 mercruiser, 21 years old and NEVER used oil! So what was the deal!??

After talking on this site and hearing that Mobil 1 was so friggin slick the rings in a new engine wouldn't seat. So at 30 hours, I changed the oil and put in good ol 30W Valvoline.

Low and behold, 10 hours of use and it hasn't came off the full mark on the dipstick. I'm thinking of going back to Mobil 1 when I change for the spring, but....I"m pretty dang confused!!

Any ideas?? WTF???

[mikeyt]

I'd stick with the Valvoline.....we've discussed the use of synthetic oils elsewhere and i still dont think they're worth it unless you have a high performance engine.

[ShabahZ280]

My friend had a 502 Mag in his Baja, and it drank oil. When he asked the local marina's service department, they said "Oh yeah, the 502's got a reputation of being an oil hog" Maybe it's normal?

[Z 202]

Yes. Any rebuilt motor should always use conventional oil for the break in, for exactly the reason you've stated.

I'm with Mike, synthetics are really not necessary. I spoke with the guy who was winterizing my boat, and he stated pretty much the same thing. He uses a straight weight (non-detergent) conventional oil in all the boats they service. He also recommended changing it at 50 hour intervals, if you boat more than that in a season.

They will use synth only if the owner absolutely wants it.

[moondance100]

hmmm...well, it doesn't use oil with regular dino oil, but I always thought the synthetic was better. As far as it being "worth the money",compared to what I spend boating, the cost of the oil is a drop in the bucket! I used Valvoline back in the 70's, 80's and part of the 90's. But, I've used mobil 1 in my trucks and cars for quite a while and I've always had good luck. Had a few of them run over 200,000 with no issues. Was this because of the mobil 1?? Who knows??

I think I'll try mobil 1 in the spring and see what it does. And if it uses oil again with the synthetic, then I"m back on dino for good!

[gjackson78]

Moondance 100
I don't work for any oil company but based on the extensice research of myself & other boaters it may be worth your time to at least review the research on Amsoil's website www.amsoil.com It's very informative. Not all synthethics are created equal.

[Tom]

I have used Mobil 1 20-50 synthetic in our '94 Talari with the 4.3 for the past two years. We've never lost a drop of oil nor had any problems with it. Our hour meter reads about 230.

[jgreen]

Here's an interesting write-up on breaking in engines and syn oil.
http://www.mototuneusa.com/break_in_secrets.htm
Pretty interesting insight.

[JohnZ202]

My two cents ... I had been chasing oil pressure issues from the beginning, (bought my boat new). After coming back to idle after a run, the oil pressure would fall quite low but not low enough to set the alarm off. Halfway through my second season I ran into a guy on the lake with a go-fast boat. His take on my problem was using multi weight oil and suggested going to a straight 40w racing oil. I've been a lifelong Valvoline user by the way.

Anyway, changed to the 40w and low oil pressure disappeared. Still not 100% convinced, I contacted Mercury and got to talk to a very helpful tech. He fully agreed with the go-fast guy and said that Merc will often suggest the racing oil.

Bottom line is marine engines operate at constant speeds under constant load. Auto engines don't, varying speeds, loads, up and down hills etc, and require the multi weight oil to serve the wider range of service.

[jgreen]

I agree 100% John. I was also taught that (for example) 10W40 oil is ten weight oil with additives in it to make it act like 40 weight when hot. Our boats run cooler than cars so the oil would never get up to it's full viscosity potential.
My only concern with the straight 40 weight would be at cold start up. Extra warm up time would be prudent IMHO.