oil for OMC 30 or 15-40 grade?

[truebrit]

According to OMC the reccommended oil for my OMC Cobra 5 ltr petrol is straight 30, the engine is based on the Ford 302 cu in block, mercruiser reccomend 15-40 for their 5 litre based on the same engine.As 15-40 is far easier to find on the shelves,can anybody throw any light or their views as to the pros and cons of either oil. (I always use greased lightening marine ptfe addittive anyway,it saved me from a major engine seize when an oil filter seal blew and emptied the sump into the bilges in seconds!!)

<hr width=100% size=1>Mike....... V8s are sweet music

 

[andrewbarker]

15-40 or even 10-40 definitely - straight 30 doesn't have the temp. range & the modern oils are just better. Given that acceleration/deceleration forces top & bottom of the con rods are less on your V8 than on a 6 or a 4 I would go for 10-40. Just make sure it's A3/B3 rated. Halford's had an offer on last weekend - buy 5l, get another half price.
Don't know if it's still on though.
Actually, what I used to use in my V8 was Millers racing synthetic 15-40 or Mobil 1 competition 15-40. Note - this isn't the usual mobil 1 which is 0-50 or 60 & IMHO too thin. Probably total overkill anyway.

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[ArthurWood]

15w40

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