0w-40 for everything

Yes, there will be a difference, the question really is how much of a difference and does it matter?

Besides there is a reason why bypass is set to work on pressure and not the flow. If it’s set at 100psi, the pump will go into bypass at 100psi regardless of oil viscosity because at that point there is more then enough oil flow in the system.

It’s a protection mechanism and just because the pump is in bypass, doesn’t mean there isn’t enough oil going through the system. That would be one stupid design.
I think at warm ambient starts the difference is negligible. I did notice on my 2019 VW - that has an oil temp readout on the DIC - that the engine oil reported cooler on the 0W20 than on the 5W40 the dealer put in "by mistake on purpose".

There is also a lot of heat generated in piston-cylinder wall shearing of the oil. - where there is much more surface area than the total of bearing area - but possibly less volume in shear at any given rpm.

I agree with @kschachn that a higher viscosity oil will heat faster from a cold ambient start due to energy lost to shearing the viscous fluid in the bearings - and on the cam profiles and on the cylinder walls.

This is primarily why lower vis lubricants provide better F.E

-Ken
 
In your applications I think 0W40 would be a good choice, for everything.
The GTO sees some really high startup pressures on cold days with the 15w-40 I was running, and I have heard of Pontiacs shearing the oil pump drive pin. Seems like an easy change with no downside to just change to something thinner at startup. Could go M1 5w-40 if I start seeing lower pressures after full warmup and beating on it too much, that would probably work just as well for all of the vehicles I mentioned.
 
In my life, the term "significant" is a very precise statistical term that means not due to random chance - essentially it means "real". When someone says something is not significant, it means it is due to random chance, that it's not a "real" difference, hence my confusion when you said there was a difference but not a real difference. I appreciate you taking the time to explain your thoughts.


Without an objective standard to define “significant” your point is moot. “Very precise statistical term” for what exactly?

“Not significant” and “due to random chance” are vastly different. An objective standard may define significant according to some metric. Being less than that metric and thus not significant doesn’t mean that the phenomena observed is random chance.
 
Aside from our 4Runner having a warranty, I’d be the same way.

Rotella T6 5w30 or Castrol 5w30 A3/B4 would be another good choice, but I am not sure if the API rating would be an issue.
 
this Is a sound plan.
I get tired of buying jugs and quarts of different oils for different vehicles to get about the right amount for each. I'm wondering whether I can just run 0w-40 Mobil 1 for all of these, just buy jugs and clear out some shelf space:

2016 6.0 vortec 2500hd with 105k miles
65 GTO 505 cid pontiac v8 with mild hydraulic roller
1997 jeep tj 4.0 with 220k miles
1972 k10'with mild flat tappet 396
2007 subaru outback with 4 cyl non turbo and 110k miles
brand new toyota 4runner

currently have all but the toyota and looking to trade subaru in on 4runner in year or two.

Are there any applications on this list where Mobil 1 0w-40 is genuinely a bad choice? I realize there may be incrementally better choices for individual vehicles, but if I run M1 0w-40 in all of these, am I really risking anything?
sound plan. no reason to overcomplicate things. I have had success running m1 0w40 in many modern vehicles and a lawnmower.
 
I'm guessing flat tappet cam and lifter wear with the 0 weight.

One more anecdotal post: I used Mobil 1 0w-40 in many vintage cars with flat tappet engines, both solid and hydraulic. Including many vintage Ford Galaxies, vintage Mustangs, vintage Shelby Mustangs, Triumph TR-4a & Spitfires, and Jaguar e-types.

I’m using it in my 2002 Jaguar XKR and Honda lawnmower too. Not sure the year model of the lawnmower, but it’s at least 12 years old.

Not counting the lawnmower, there’s at least 200,000 cumulative miles on those vehicles over a 1-2 decade span.

I know they are not the same engine as the OP, but just another example of using a pretty good “no-issues” oil, and living to tell about it.

Z
 
I would not use it on the 65 or 72.
That's odd. The M1 0W40 is the oil I have been switching my vehicles over to. I've currently used it in two flat tappet cam engines, both with fast ramp hyd flat tappet cams and stiffer than stock springs. It's been doing great in both of them and the engines are noticeably smoother sounding with it as well. No zddp additive needed with it, either.
 
I've routinely used M1 0w40 in both my flat-tappet Chrysler 440 Magnum engines, as well as an AMC 360 and a Jeep 4.0. Works great... I just had the distributor out of one of the 440s to re-curve it a little and took a look at the cam while the hole was open. Absolutely spotless, and a very healthy lifter/lobe contact pattern as well as oil pump drive gear contact pattern... although since that particular cam and lifters were made in the 1990s, I'm sure they'd be fine on any name brand off-the-shelf oil ranging from 10w30 to 0w40. (in case you can't guess, I blame the "flat tappet cam crisis" on the cam and lifter manufacturing processes, not oil. I've seen too many "I used high-ZDDP break in oil, followed the procedure to the letter, and a lobe still went flat!" stories to think otherwise.)
 
I get tired of buying jugs and quarts of different oils for different vehicles to get about the right amount for each. I'm wondering whether I can just run 0w-40 Mobil 1 for all of these, just buy jugs and clear out some shelf space:

2016 6.0 vortec 2500hd with 105k miles
65 GTO 505 cid pontiac v8 with mild hydraulic roller
1997 jeep tj 4.0 with 220k miles
1972 k10'with mild flat tappet 396
2007 subaru outback with 4 cyl non turbo and 110k miles
brand new toyota 4runner

currently have all but the toyota and looking to trade subaru in on 4runner in year or two.

Are there any applications on this list where Mobil 1 0w-40 is genuinely a bad choice? I realize there may be incrementally better choices for individual vehicles, but if I run M1 0w-40 in all of these, am I really risking anything?

I would look for or have a VOA performed on a RECENT batch of M1 0W40 before using it "naked" in the K10 and TJ. Make sure there is appropriate zinc for those engines. Everything else should be fine.

Rather than having a separate/different oil for those engines (if needed?), consider a zddp boosting additive. Careful, they are all snake oil, except the one that is approved by BITOG, which varies depending on seasonal feelings.
 
Rather than having a separate/different oil for those engines (if needed?), consider a zddp boosting additive. Careful, they are all snake oil, except the one that is approved by BITOG, which varies depending on seasonal feelings.
You’ve got several simultaneous misconceptions going on… from zinc being what an oil needs, to using a zddp additive. You’re always safer using a fully-formulated oil to protect your engine rather than playing backyard chemist.

There are several oils available that will protect even flat-tappet cams without ever needing anything “extra” than what the oil blender put in the container. Amsoil Z-Rod, HPL CK-4 are two great choices. As shown by others, the M1 FS 0w40 is more than capable as well.
 
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