5W30 or 10W30, synthetic or traditional? Opinions wanted

* Over 120,000 psi = FANTASTIC wear protection

* 105,000 to 120,000 psi = INCREDIBLE wear protection

* 90,000 to 105,000 psi = OUTSTANDING wear protection

* 75,000 to 90,000 psi = GOOD wear protection

* 60,000 to 75,000 psi = MODERATE wear protection

* 50,000 to 60,000 psi = UNDESIRABLE LOW wear protection

* Below 50,000 psi = CAUTION – EXTREMELY LOW wear protection

The HIGHER the psi value, the BETTER the Wear Protection.

What I use:
''• 10W30 LE (Lubrication Engineers) Monolec Ultra Diesel oil, API CK-4, CJ-4, CI-4, CH-4, CI-4Plus, conventional = 97,878 psi
This oil was tested Spring 2018. It is the best performing CK-4 Diesel oil I have tested to date. And it is the second best performing Diesel oil I have ever tested.''

I know it says Diesel but it used to be for gasoline also until recently.

It's a monster of a read, but what you use may be listed.

The advice I got from a mechanic friend was to use the same type of oil that was used to break in the engine, i.e. synthetic or conventional and once you hit 120K miles use the high mileage oil in a weight that suits your normal environment temperature wise.

So I use conventional 10W40 in summer and 10W30 in winter. I live in Houston. My manual recommends 5W30 but I figure that's for the warranty period. I'm over 250K miles now on my '94 4.3L GMC so I use the heavier conventional oil. I'm looking at getting 400K miles.

Also be careful not to overfill the oil or transmission fluid.

Drunkcanuk said:

I think what they are alluding too is this question has as many answers as those who answer it. Everyone has different opinions on oil. I would default to the original OE spec oil, as this is what the lawyers and engineering agreed upon to be comfortable offering a warranty.

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Yeah but you are forgetting that they only offered warranties for so long, and certainly not high milers. My motor is nearing 260K so you can bet that clearances are a tad bigger than when the motor was new and tight. For that reason I use something a bit thicker as in 5W40 and that's on the recommendation of a lifelong mechanic.

So then, we just need to determine who has the best mechanic.

FYI - the 5w-30 was recommended/required by manufacturers so they could meet C.A.F.E. standards, not necessarily engine design and tolerances.

Mercedes had a lot tighter tolerances than U.S. brands and they (and BMW) recommend European spec Mobil1 0w-40, at least in my 2004 Chrysler Crossfire which had the same drive train and chassis as their SLK320 model. Maybe @someotherguy can enlighten us on his 300s?

And I swore I wasn't gonna get into another "best oil" thread -

PlayingWithTBI said:

FYI - the 5w-30 was recommended/required by manufacturers so they could meet C.A.F.E. standards, not necessarily engine design and tolerances.

Mercedes had a lot tighter tolerances than U.S. brands and they (and BMW) recommend European spec Mobil1 0w-40, at least in my 2004 Chrysler Crossfire which had the same drive train and chassis as their SLK320 model. Maybe @someotherguy can enlighten us on his 300s?

And I swore I wasn't gonna get into another "best oil" thread -

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As an owner of several German performance cars across the years (and looking forward to the next one) I can confirm this.

PlayingWithTBI said:

FYI - the 5w-30 was recommended/required by manufacturers so they could meet C.A.F.E. standards, not necessarily engine design and tolerances.

Mercedes had a lot tighter tolerances than U.S. brands and they (and BMW) recommend European spec Mobil1 0w-40, at least in my 2004 Chrysler Crossfire which had the same drive train and chassis as their SLK320 model. Maybe @someotherguy can enlighten us on his 300s?

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I think, the European emission testing is done starting with a cold engine - which obviously leans on the xxW side of the viscosity.
I'm wary of oils with significantly different numbers. The xxW is oil. The other number is made up with viscosity improvers (long chain polymers) which get 'chopped up' in service costing the oil its viscosity in time. The bigger the number span, the greater the reliance on VIs.

PlayingWithTBI said:

And I swore I wasn't gonna get into another "best oil" thread -

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You and me both!

Pinger said:

I'm wary of oils with significantly different numbers. The xxW is oil. The other number is made up with viscosity improvers (long chain polymers)

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I think this is good reasoning. Some companies have claimed to not use VI improvers, at least not for 10W-30, But how is a guy to know? Impossible! Especially as the oils are frequently reformulated. If the cold start properties of 0w-30 is not needed, don´t use it. But if changed reasonably often it will not have time to brake down enough for it to matter.

But before I would use ANY 0W-30 oil in my old pickup I would look up the REAL CST rating@100 degrees C, just a tip, as I´m sure some of them might be juuust thick enough not to be rated as 0w-20

1990Z71Swede said:

I think this is good reasoning. Some companies have claimed to not use VI improvers, at least not for 10W-30, But how is a guy to know? Impossible! Especially as the oils are frequently reformulated.

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I don't think it is possible to have a multi-grade oil without VIs. It was the advent of VIs that made multi-grades possible rather than just the 'straight' oils previously.
I was once told that large marine engines still use straight grade oils to avoid the VIs of multi-grades because with the gear driven auxiliary PTOs present, they would be particularly hard on VIs. Large marine engines though aren't troubled with frequent cold starts.

Schurkey said:

...REAL synthetic oil is typically made from natural gas. USA-Phony "synthetic" is crude oil that's had Van Halen played at astronomical volume levels until the crude oil submits...

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Are we talking about Roth or Hagar here??