hi all, been lurking for sometime, and have a question. i have a 1994 four winns boat, with an efi 5.8L motor. have been using castrol hd30 oil for sometime now. thinking about switching to delo 30 wt. any thoughts? OMC recommends against using multi grade per the manual, and doesn't comment on synthetic use. what is the difference on oils labeled "marine"? please help! thanks, todd.

 

Thanks for joining us at FTE!

DELO 400 is used for all types of marine engines, diesel and gas. When I worked offshore oil, DELO was used almost exclusivly in the crew boats, work boats and escape craft as well as the cranes and all the diesel driven equipment on the platform.

I'm don't know of any special requirement for marine engines that aren't met by oils like DELO, Rotella T, or Delvac. So I don't know what's different on oils labled "marine." Perhaps it's just consumer marketing information. Like if you buy a quart of oil at a parts store or gas station and the label says "for cars and trucks."

Other oils for marine use, like gear lube or hydraulic oil, may have demulsifier's to minimize mixing and contamination with water.

 

thanks for the info. are any of the oils you mentioned better than a straight hd30 wt? i was also thinking about using chevron supreme 30 wt. i have been using mobil 1 1030 in all my vehicles since 1984, and have been very pleased, but am miffed by the fact that no marine mechanic can tell my why no one uses synthetics in boats. perhaps because the thermostat is 140 degrees, and boats arent subjected to wide temp extremes like cars or trucks? another thing concerns me, is the shear strength of the oil ( is that the right term?) the motor redlines at 4600 rpm, and usually i run at least 4000 to 4400 all the time. thanks again, todd.

 

All the brands I mentioned make a 15w40 oil, which is probably the most commonly recommended viscosity for four cycle diesel engines. Better is relative to the variations in temperature extreme. The multi-vis 15w40 will give a little broader coverage. But straight 30w is generally good from 32*-104*. So if your use falls in between there, a straight 30 would certainly be okay. High quality heavy-duty oils are highly resistant to viscosity shear-down. I don't think a synthetic lubricant would give you a huge benefit and I'm guessing you have way shorter drain intervals than an automobile, so it wouldn't really be economic. But unless there is some special marine rating that an SL/CF rated oil doesn't meet, I don't see why you couldn't use Mobil 1 either.

 

My '86 MerCruiser 260 was specced for straight 30W, but Mercury had a retro active change to 25W-40. This is what I have been using for the last 5 years with no problems. I can only get it in the MerCruiser or Quicksilver (same thing) brand. I have never seen another brand in that wieght.

My cuz ran Mobil1 in his MerCruiser 350 Magnum for 10 years. He ran hard and fast with 150hrs a season. One day he sucked a valve and with the heads off the cylinders still had the cross hatch pattern on them. The thing still runs like the day it was dropped in there.