0W40?

[Paul Workman]

Originally Posted by Hib Halverson

Playing the devil's advocate...

LT5s with stock valve train don't need that level of zinc and phosphorous (which was formulated with pushrod valve gear in mind) because the cams act directly on the tappets. There are no pushrods and no rocker arms. That means less mass and since there is less mass, even the stock 1G LT5 valve springs have significantly less tension than valve springs in pushrod engines, thus the pressure over the nose is less and...there is less need for the extreme pressure additive ZDDP.

I no longer have Mobil 1 data sheets going back to the 90s so I can't quote facts, but I'm not convinced that all the factory fill oil used back then has 1200-1300 PPM phos.

NOT necessarily taking exception to what you stated re lighter mechanicals, i.e., pushrods and rockers, and spring tensions, etc. But, but, but! In the interest of physics, does not the forces to overcome inertia increase @ the square of the rate of acceleration (of the parts involved), AND therefore the task of the lubricity in the oil?

Again, the issue is direct vs. indirect "testing". Direct testing on the 1G LT5 is cost prohibitive, especially considering the lack of new or substitute parts. And, it takes significant runtime/stress testing to gather evidence enough to make any scientific, definitive conclusion(s). So, in absents of direct testing, we're relegated/obliged to accept INDIRECT test data results gathered with other (engines) operating with identical or at least practically close conditions.

My point is, the data for making a direct comparison(s) and much less predictions between results of this latest (Mobil 1) oil and that of products having considerably more real runtime data on actual 1G LT5s rests solely on a manufacture's reputation and little if anything else - comparatively speaking.

EXAMPLE: Various antifreeze makers provided a revolutionary coolant (referred to commonly as DEXCOOL; a coolant improvement over the traditional (GREEN) silicon base coolant which "Dex" superseded. But, if one were to replace their GREEN stuff with DEXCOOL solely on the assumption that the "DEX" was made by a reputable company and therefore suitable for their LT5, they were in for a very expensive mistake. Companies like Mobil 1 make a variety of products for various applications. But, applications differ, and one size does not always fit all!

Your mileage may vary....

[Dynomite]

Originally Posted by Hib Halverson

Starting in 2019, GM changed to a 0W40 engine oil for all Corvette engines except the LT6 which uses a 5W50.

Has anyone tried a 0W40 in the first generation LT5?

I would think that the same two major advantages?1) oil gets to bearings more quickly on cold starts and 2) better thermal stability during aggressive engine operation?that GM gained with using a 0W40 in the 2G LT5 and the LT2 woulid be useful in the original LT5.

What is the maximum cam pressure on the lifter for an LT5 engine?

Going from a 4,000 rpm to over a 7,000 rpm engine is a BIG factor in Cam Pressure and wear.

I also know from an experience that the cam tips are not parallel with the Lifter surface on the LT5 engine. (Cam Tip being the high "edge" of the Cam that gives the Lifter maximum compression).

An Aberration in Cam Wear

The localized pressure on the lifter must be very difficult to determine in that case....

The Cam Wear on the tips can be seen on the Cams pictured below.



I assume the cam tip being tilted and off center on the Lifter surface keeps the lifter rotating. The lifter rotating under the cam acts like a rolling intersection (not purely frictional). [B]The surface of the Lifter is moving vertically and horizontaly as the Cam Tip slides/rolls across the Lifter. (It is hard to imagine this happening up to 60 times a second).

Redline (maximum safe operational engine speed) is a BIG factor on ZDDP issues.....

Redline for L98 is 5,500 rpm.
Redline for LT5 is 7,200 rpm.

Mobile-1 for racing engines (high rpm) shows much higher ZDDP

Originally Posted by spork2367

https://www.mobil.com/lubricants/-/m...pecs-guide.pdf

Notice the zinc and phosphorus content on the racing oils...

Post 294 - Camshaft Abnormal Wear

A little more detail on Oil/Zinc/Cam Wear from Hib Halverson........

Oil/Zinc/Cam Wear Part 1

Oil/Zinc/Cam Wear Part 2

[spork2367]

https://www.mobil.com/lubricants/-/m...pecs-guide.pdf

Notice on every Mobile 1 oil with API certification the recommendation states "Vehicles that require XW‐
XX."

There is not one spot in their product guide that recommends using a viscosity not originally recommended by the manufacturer.

Notice the zinc and phosphorus content on the racing oils...

Again, this whole topic is grayed significantly by the regulations governing oil, fuel economy, emissions equipment, etc. Aviation oil still has or recommends as an additive, Tris(methylphenyl)phosphate (Tritricresyl phosphate). Long banned in automotive oils and with relatively high toxicity, but in a market that is widely unregulated. A market that suffered many of the same issues listed in Hib's articles, such as the ceasing of lifter production by Eaton who's secret sauce recipe for lifters supplied aviation for a long time.

Another good read for those who really want to get into the weeds: https://www.mdpi.com/2075-4442/1/4/132/htm

[tiegsd]

Originally Posted by spork2367

https://www.mobil.com/lubricants/-/m...pecs-guide.pdf

Notice on every Mobile 1 oil with API certification the recommendation states "Vehicles that require XW‐
XX."

There is not one spot in their product guide that recommends using a viscosity not originally recommended by the manufacturer.

Notice the zinc and phosphorus content on the racing oils...

Again, this whole topic is grayed significantly by the regulations governing oil, fuel economy, emissions equipment, etc. Aviation oil still has or recommends as an additive, Tris(methylphenyl)phosphate (Tritricresyl phosphate). Long banned in automotive oils and with relatively high toxicity, but in a market that is widely unregulated. A market that suffered many of the same issues listed in Hib's articles, such as the ceasing of lifter production by Eaton who's secret sauce recipe for lifters supplied aviation for a long time.

Another good read for those who really want to get into the weeds: https://www.mdpi.com/2075-4442/1/4/132/htm

Interesting stuff for the engineering types out there. The paper gives a sense of the complexities if tribology, and the difficulty in balancing advantages and disadvantages of various additives for oil manufacturers.


My takeaways: motor oils are not all created equal; stick with what is known to work unless there's good reason not to; the devil is in the details.


Appreciate the reads!

[tiegsd]

Originally Posted by Dynomite

What is the maximum cam pressure on the lifter for an LT5 engine?
Going from a 4,000 rpm to over a 7,000 rpm engine is a BIG factor in Cam Pressure and wear.

I also know from an experience that the cam tips are not parallel with the Lifter surface on the LT5 engine. (Cam Tip being the high "edge" of the Cam that gives the Lifter maximum compression).

An Aberation in Cam Wear

The localized pressure on the lifter must be very difficult to determine in that case....

The Cam Wear on the tips can be seen on the Cams pictured below.



I assume the cam tip being tilted and off center on the Lifter surface keeps the lifter rotating. The lifter rotating under the cam acts like a rolling intersection (not purely frictional). [B]The surface of the Lifter is moving vertically and horizontaly as the Cam Tip slides/rolls across the Lifter. (It is hard to imagine this happening up to 60 times a second).

Post 294 - Camshaft Abnormal Wear

A little more detail on Oil/Zinc/Cam Wear from Hib Halverson........

Oil/Zinc/Cam Wear Part 1

Oil/Zinc/Cam Wear Part 2

Thanks for the pointers to these articles. I imagine this is about as detailed a history as you are going to find anywhere on the topic.



Early in the Part 1 article, it is stated that the LT-5 having flat tappets is "... only peripherally related to this wear issue, because it had overhead cams and direct acting, bucket-type flat tappets." It would seem to imply that the LT-5 operating conditions are less severe, but I may be reading to much into that statement.


I'd be interested to know what drove the choice of ZDDP content for the LT-5 and whether it's valve train design is a more or less (or neither) severe case in terms of valve train loading and wear compared to older flat tappet OHV engine designs.


Also, if anyone knows, whether the recommended oil for the LT-5 changed at all between the different model years?

[spork2367]

Originally Posted by tiegsd

I'd be interested to know what drove the choice of ZDDP content for the LT-5 and whether it's valve train design is a more or less (or neither) severe case in terms of valve train loading and wear compared to older flat tappet OHV engine designs.

It's generally accepted to be less severe than high performance pushrod engines. It's probably equal to or more severe than low performance pushrod engines.

However, emissions equipment life drove the ZDDP content for all API approved engine oils. Zinc deposits can reduce catalytic converter life. Interestingly, I haven't found any great articles on how much zinc reduces the catalyst life by how much.

[Dynomite]

Redline (maximum safe operational engine speed) is a BIG factor on ZDDP requirement issues.....

Redline for L98 is 5,500 rpm.
Redline for LT5 is 7,200 rpm.

Mobile-1 for racing engines (high rpm) shows much higher ZDDP

Originally Posted by spork2367

https://www.mobil.com/lubricants/-/m...pecs-guide.pdf

Notice the zinc and phosphorus content on the racing oils...