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10W30 Vs. 10W40 Motor Oil


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Hello everyone

Im Big Fink, I really need some help tryin' to figure out what kinda motor oil I wanna swich too. since i have over 180k miles im switchin' all my fluids to High Millage. I was lookin' into Castrol High Milleage,does anybody use it and if you do could you tell me if it is any good? Ok the real ? is would it work if i swich from 10w30 to 10w40 motor oil? how about sythetic motor oil. i got the 4.9L Engine and I wasnt sure so I figured this whould be the best place for me to find out yall help'd me out incredbly last time I posted Please help me agian.

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The car calls for 10W30, you won't gain any appreciable benefit using synthetic oils. You engine is suseptible to a number one main bearing knock. It is especially prominent in the summer months when the oil is very hot. If you experience this you may benefit from mixing in some 10W40. It has been suggested that Rotella 15W40 oil would be helpful in the hot summer months, but don't use it in cold weather. Personally I like to act more conservatively, in the warmer months when you change your oil use two quarts of 10W40 and see how the engine reacts, if you like the results next time try 3 quarts, but do it in small steps. I had the number one main bearing knock in my 91 Seville 4.9 and in the summer months I used 10W40 100% with no trouble. The car however was often in bumper to bumper new york city traffic. The 4.9 is a good engine. I do believe that you can use 10W40 but its best to be conservative. I tried to use it only when the conditions called for it.

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The best oil for your application is one of the heavy duty diesel motor oils that are SL rated and sold under the Delo/Delvac/Rotella brand names depending on what is available and/or whether you like Chevron/Mobil/Shell oils....

I could not agree more.

I've been using Esso/Exxon XD3 since 1967 in ALL my cars. It's in the same category as Delo/Delvac/Rotella etc.

The cost is a little more than the "off the shelf" brands, however it is far superior and costs much less than a synthetic.

The local Police force here uses XD3 in all their fleet.

Barry

P.S. My lawn mower and snow blower get the same oil. They are both older than most people on this board.

2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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Not sure what is to be gained by "creeping up on it" by adding one quart at a time....LOL

That's just me, Mr. Belt and Suspenders..... Since the engine calls for 10W30, I try not to contradict the manufacturer (who the hell am I? LOL). Thanks Guru..

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P.S.  My lawn mower and snow blower get the same oil.  They are both older than most people on this board.

Is it a "Lawn Boy" by any chance?

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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allright i changed my oil today,i decided to go with castrol 10w30 high millage i asked a cadillac mechanic he said it would work well,must admit Pearl is runnin a hole lot smoother.

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Back in the summer months I switched to a Full Synthetic Oil, I was told a few weeks later on the Board that there is no need for it in the Northstar and it was a waste of money. Is a generic 10W-30 the best choice then?

"Cadillac, it's not a car, it's an obsession"

-W.Kingdon

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P.S.  My lawn mower and snow blower get the same oil.  They are both older than most people on this board.

Is it a "Lawn Boy" by any chance?

No, it's a generic store brand with a 3.5 B&S engine.

I thought Lawn Boys were two cycle .

Barry

2008 STS V8
2016 Colorado Z71
1970 Corvette LT-1 Coupe

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The closer the numbers, the less elastomers, polimers, rubberbands :P or something like that is in the oil. The stuff that make a 10w act like a 30w when hot. That stuff tends to develope sludge (or at least it used to) so the less the better. Guru HELP! Other than that, I have never heard "the closer the numbers, the better the oil".

Oh, you already did, darn, your fast :P

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  • 2 weeks later...

I need to change the oil, and I have 96,000 miles right now. Will Rotella 15W40 be a good choice? They are very cheap at COSTCO right now.

Bbobynski please advise.

1960 Sedan De Ville (sold)

1970 Coupe De Ville (sold)

1987 Mazda RX-7 (sold)

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