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Choice of Oil to use OMC 30

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mark chisholm

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"just wondering if you really

"just wondering if you really have to use the OMC brand Oil for my engine. rebuuilt a month ago, runs great, and when i went to a local marine service place, they highly suggested using the omc brand motor oil, quite a bit more expensive than normal car motor oil. Seeing as this is just a GM engine, is there any harm in running normal motor oil through it? or does it have to be marine grade engine oil?"
 
"There really isn't a mari

"There really isn't a marine grade oil. Diesel engines reguire a differently rated oil, which can also be used in gasoline engines but of course that does not concern this situation. A 10W-40 oil would be excellent unless it has been run on straight 40 weight oil previously. It is a good idea to choise a brand of oil and use it exclusely, at least from oil change to oil change as each manufacturer uses a precise package of additives in their product. Note the API rating on the bottle. It should be up to API-SM for best results"
 
"Yikes, Marine engines should

"Yikes, Marine engines should never run on 10W based multi grades. Straight 30 weight, or 25W40 ONLY! 20W50 in a pinch.
Anthony has been very lucky.
As far as API ratings, I'd think you would have to be shopping in the third world, or at a museum to find one that wasn't the latest API rated oil."
 
"Hy Stat, API rating is up to

"Hy Stat, API rating is up to API-SM. Some small stores with slow moving stock still have API-SJ on their shelves.
Engineers of marine engines tend to prefer that you use heavier viscosity oil than in their automotive counterparts but I've seen lots of people using 10W-40 with good results. The main point is that that it's not the brand that is important here."
 
"You are right on the brand th

"You are right on the brand thing...Walmart doesn't have a refinery.... and the worst SM or SJ oil there is ten times better than the best oil on the market 20 years ago. I guess if the 2 oils are sitting side by side, I might grab the SM oil if it were the same price. But at the time OMC went out of business SF wasn't even on the shelves....and with the exception of the Ford 2.3 (1970's design), the most sophisticated motor ever used by OMC in a stern drive is a chevy pushrod engine designed in the early 1950's and unchanged since.
I see people buying synthetics and fancy oils and them pouring them in through one of those accordian funnels that is impossible to clean the sand and dirt out of...
Cleanliness is most important."
 
"The main point is that there

"The main point is that there is no special "stuff" in any particular brand of oil over another. Theoretically a marine engine runs under constant load as opposed to an automobile engine and can benefit from a heavier viscosity oil but basically it is the same engine I know a lot of people who run 10W-40 in marine engines. In cold climates it even works better.

Fortunatley for all of us, oil ratings have been increasing to the point that engines can now easily run for 30 years and 300,000 miles in automobiles. That is provided you keep it changed regularly. What more does anyone want?"
 
"Because boats aren't driv

"Because boats aren't driven in the winter (in most areas) thin winter weight oil is not required.
In a car, you need multi grade oil because you might not get the oil out from season to season.
Best for a car would be 30 on hot days and 10 on cold days, but changing oil based on the weather is not practical.

10W40 is made from 10W base stock. Friction modifiers are added to make it act thicker in warm temperatures. However, the chemical thickeners break down eventually (like that TV ad refering to "viscosity breakdown") and you are left with the base oil.

Because boat engines rev high for longer periods of time relative to cars and never really coast or go downhill, the oil gets churned up and heated a lot which is what breaks down the friction modifiers. The load factor is much higher than a car (that's why boats use so much gas) and that makes the internal parts run hotter.

The oil pressure gauge is important - if the oil pressure is good with 10W40 then you are ok. But if an engine was built "loose" ,(more clearance between bearings and crank journals), or age makes those clearances wear I would worry that oil pressure will drop below the safe range.
I just like to use what the manufacturer recommends. Your engine owners manual calls for straight 30 weight.

Some Volvo marine engines DO call for 10W30, but they have cold raw water supplied to an engine oil cooler which keeps the oil from getting super hot.

10 psi per 1000 rpm with a 20 psi minimum is an old rule of thumb."
 
"Stat, Thanks for the info, i

"Stat, Thanks for the info, i see your point. When i got the boat the former owner he stated that he ran 10w40 in it. He had owned it for 4 years, i assumed i should keep on keeping on with what the engine had been used to. I had considered droping 20w50 in it but i was afraid it would be to thick, compared to what the engine had been used to seeing. I agree it does turn higher rpms than a car and is under alot more load. I am thinking of switching to 25w40, due to the fact that i have noticed when im on the throttle hard the oil pressure is good , but when im idiling, it is lower than when wide open."
 
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