Question about oil viscosity

[WorkinLonghorn]

Is this a mistake? I read somewhere that lube oil for diesel engines was the way to go. Got a good deal on some 15/40 (for diesels) at Costco. Just changed the oil this morning and got to thinking maybe that is too thin. My original Owner's Manual says to use 20/40 (or straight 30wt) in the hottest climate, IE. here in L.A. Oil has come a long way since '69 so it should be good right? This is a new GM stock replacement crate motor. -BA

[Steeveedee]

Seems I read somewhere that oil for diesels isn't formulated for the higher RPM that gasoline engines run at. Other things, too. Maybe check that out.

[72c20customcamper]

Been using it for a while I buy big containers since I have two diesels . It does have less zinc than it used to Since diesels have cats on them too for the past years . But to be honest I’ve never had an oil related issue in 30 years of driving old flat tappet engines . 15-40 is more than thick enough

The 15 is when it gets to 30 degrees so it will flow like a 15 weight oil the 40 means it will still retain the viscosity of a 40 weight oil when hot . Don’t think you need to worry about the cold number .

This is a good oil for warm climates Castrol GTX Classic and at $24 for 5 quarts it’s a good deal

https://www.amazon.com/Castrol-Class...5995518&sr=8-2

[dagnabbitt]

I run Rotella in most of my vehicles but I heard that there had been some recent changes to the formulation that may remove any benefit that might have previously existed for older gas engines, probably what 72C20 is referring to. You could throw in some additives but at the end of the day might be better to just switch oil.

I just bought some of the below for my new crate motor.

https://www.summitracing.com/parts/j...EaAhEvEALw_wcB

[72SB]

OP

if your new "GM Crate motor" is a hydraulic flat tappet cam motor (like your original motor was) you need to run an oil with high zinc content or a zinc additive with conventional oil ESPECIALLY if this is a brand-new flat tappet hydraulic cam motor.

If its a newer "full" roller hydraulic cam, then conventional oil is fine and no zinc additive or high zinc oil is needed....although it never hurts. Motor oil stopped containing high levels of zinc when CATS came out, conventional or diesel oil as zinc kills CATS.

regarding your 15-40 diesel oil, the weight is not an issue although weight depends on how main bearing clearances are set up. Stock original motors are typically 10-30 but often performance build motors have a "slightly" wider bearing clearance so 20-50 is spec so there is a bigger oil wedge between crank and bearing for higher than 5500 rpm use.

For flat tappet hydraulic cam or solid lifter motors I use Valvoline VR1 racing oil as it has high zinc content in 10-30. Joe Gibbs oil also

[WorkinLonghorn]

Originally Posted by 72SB

OP

if your new "GM Crate motor" is a hydraulic flat tappet cam motor (like your original motor was) you need to run an oil with high zinc content or a zinc additive with conventional oil ESPECIALLY if this is a brand-new flat tappet hydraulic cam motor.

If its a newer "full" roller hydraulic cam, then conventional oil is fine and no zinc additive or high zinc oil is needed....although it never hurts. Motor oil stopped containing high levels of zinc when CATS came out, conventional or diesel oil as zinc kills CATS.

regarding your 15-40 diesel oil, the weight is not an issue although weight depends on how main bearing clearances are set up. Stock original motors are typically 10-30 but often performance build motors have a "slightly" wider bearing clearance so 20-50 is spec so there is a bigger oil wedge between crank and bearing for higher than 5500 rpm use.

For flat tappet hydraulic cam or solid lifter motors I use Valvoline VR1 racing oil as it has high zinc content in 10-30. Joe Gibbs oil also

Thanks for this. The engine is just like stock except I believe they lowered the compression from 9-1 to 8 or 8.5-1 (can't remember). So it has the flat tappets with the usual very modest 3.90"/4.10" valve lift. It operates below 2,500 RPM unless I'm really pressing to get up a freeway on-ramp or hauling considerable weight. Maybe I'll get some additive this one time until I change it again. -BA

P.S. Bearings are very tight with Oil pressure ~30 PSI at hot idle.

[WorkinLonghorn]

Originally Posted by 72c20customcamper

Been using it for a while I buy big containers since I have two diesels . It does have less zinc than it used to Since diesels have cats on them too for the past years . But to be honest I’ve never had an oil related issue in 30 years of driving old flat tappet engines . 15-40 is more than thick enough

The 15 is when it gets to 30 degrees so it will flow like a 15 weight oil the 40 means it will still retain the viscosity of a 40 weight oil when hot . Don’t think you need to worry about the cold number .

This is a good oil for warm climates Castrol GTX Classic and at $24 for 5 quarts it’s a good deal

https://www.amazon.com/Castrol-Class...5995518&sr=8-2

WOW, I've never seen this. Just added to my "cart". Thanks -BA

[WorkinLonghorn]

Originally Posted by Steeveedee

Seems I read somewhere that oil for diesels isn't formulated for the higher RPM that gasoline engines run at. Other things, too. Maybe check that out.

Now you've got me a bit concerned. This is a very low rev-ing application though and with the extremely over-square 350 I would think piston speed is low. But I'll look into this-BA

[67C10Step]

Originally Posted by dagnabbitt

I run Rotella in most of my vehicles but I heard that there had been some recent changes to the formulation that may remove any benefit that might have previously existed for older gas engines, probably what 72C20 is referring to. You could throw in some additives but at the end of the day might be better to just switch oil.

I just bought some of the below for my new crate motor.

https://www.summitracing.com/parts/j...EaAhEvEALw_wcB

Now you show me this? Right after I just placed my latest Amazon order. I know what will be in my next cart for purchase. Thanks for that.

[54blackhornet]

I live in a rural area and run 15/40 Dello 400 in all my older vehicles and equipment. My Onan generators that power the property have a combined run time of over 30 thousand hours total. I have never had any engine issues running this oil. My 71 C/20 has run on it since 2003. I do religiously change it every 100 hours in regards to the generators and every 3000 miles for the pickup.

[Steeveedee]

Originally Posted by WorkinLonghorn

Now you've got me a bit concerned. This is a very low rev-ing application though and with the extremely over-square 350 I would think piston speed is low. But I'll look into this-BA

Here's the article I remember. Interesting reading.

https://www.motortrend.com/how-to/di...soline-engine/

[dagnabbitt]

Originally Posted by Steeveedee

Here's the article I remember. Interesting reading.

https://www.motortrend.com/how-to/di...soline-engine/

It is in this article that I learned that yes, you can have too much zinc. That is why I try to stay away from additives. IMO whatever oil you choose to run should have everything in it that the manufacture requires.

[WorkinLonghorn]

Originally Posted by Steeveedee

Here's the article I remember. Interesting reading.

https://www.motortrend.com/how-to/di...soline-engine/

A very good read. Thanks Steve. It seems like I did make a mistake but this article is clearly about race engines and hot-rods which this truck is no where close. But now I'm thinking. Maybe just use some regular 20/40 or 30wt. But drain out the brand new oil? Probably not. As mentioned, 3.90" Intake valve lift and 4.10" exhaust at 2-2,500 RPM, open valve spring pressure was ~200 Lbs stock. -BA

[Ironangel]

I use to run Rotella T 15-40 in everything I own, from an 80 KZ-1000 drag bike to my all my old Chevy's. Never an oil related issue...Then I heard Rotella T was dropping the ZDDP content so I went to MAG1 for the small blocks, Valvoline VR1 for the big block, and Amsoil for the bike...PS. I sold the KZ-1000 years ago, I ride an Indian now...

['68OrangeSunshine]

I use Valvoline VR1 SAE 30 in my 292.

[Steeveedee]

Originally Posted by WorkinLonghorn

A very good read. Thanks Steve. It seems like I did make a mistake but this article is clearly about race engines and hot-rods which this truck is no where close. But now I'm thinking. Maybe just use some regular 20/40 or 30wt. But drain out the brand new oil? Probably not. As mentioned, 3.90" Intake valve lift and 4.10" exhaust at 2-2,500 RPM, open valve spring pressure was ~200 Lbs stock. -BA

Given how you are driving it, I doubt that that oil is going to hurt it.

[72SB]

Originally Posted by dagnabbitt

It is in this article that I learned that yes, you can have too much zinc. That is why I try to stay away from additives. IMO whatever oil you choose to run should have everything in it that the manufacture requires.

You do understand all regular oil made now does not contain the ZDDP (zinc) oil did when our 70's motors were new, right?

When Catalytic converters were mandated oil companies had to re=formulate their blend considerably reducing zinc levels.

Flat tappet hydraulic and solid lifter cam motors like our original, and some rebuilds, have flat tappet cam motors and still require oil as it was pre CAT oil blend. This is why a zinc additive or oils like Valvoline and Castrol "racing oil" are made and should be used. Those higher zinc blend oils (like oil used to be) say right on bottle not recommended to cars with catalytic converters (it kills CATS)

https://www.amazon.com/gp/product/B0...e?ie=UTF8&th=1

I buy Valvoline VR1 10-30 on Amazon as whatever auto part stores just carry the 20-50 weight.

[OregonNed]

Using Brad Penn oil now - love it

[mrein3]

My thoughts on modern oil and cams...

I flattend out 3 or 4 or 5 cams in my 350 that came with my truck. I finally gave up and built a flat tappet 383. I broke it in per cam manufacturer spec, ran only the Valvoline VR1 racing oil. And flattend out that cam after about 10,000 miles.

I installed a 307 I had laying around that has never been opened and proceeded to flatten that cam.

I have 3.73 rear end gears and a th350. I think the simple fact is we can't run these engines with crappy over the counter oil and today's highway speeds.

I have given up on flat tappet cams. I have flat tappet cams in my two Chevelles but they are only driven to the grocery store and to church on Sunday but when they do get on the road they have 2.73 rear ends and cruise along quite nicely on the open road.

My truck, which I like to take out on the road and also pull stuff with is never going to see another flat tappet cam. I have a Vortec 350 under the bench that just needs my time and a bit of my money which in this economy I never seem to have at the same time. For now we limp along, barking out of the carb and blowing smoke out of that 51 year old, never opened 307.