Jump to content

Recommended Posts

For those with flat tappet engines, what oil do you use and is the zinc content of concern to you when you choose an oil? Almost certain that I'm going with Amsoil Z-Rod 10W-30 for my next change. Just not sure if zinc is a real concern in a stock 1964 GTO that is never pushed too hard. Only street driven.

Share this post


Link to post
Share on other sites

Tired of these Ads? Register Today!

Zinc is most definitely a concern in pre 1980 (approximately) engines. Zinc in engine oil forms a protective film/lubricant on metal parts to prevent metal to metal wear. That said while Amsoil is a fine oil, in my opinion Shell’s Rotella is a better choice.

Share this post


Link to post
Share on other sites

I understand there is usually a lot of confusion around this subject and the direction Frosty is pointing is good and logical. But at the end of the day Amsoil is twice the price of Rotella T6, has no more zinc in the formula than Rotella, has a lower base number, which means a great deal and has a lower viscosity rating, which is very important. 

Question, in the same engine, running the same temperatures under the same loads using the same brand of oil which is better 10W30, 10W40 or 5W40?

Share this post


Link to post
Share on other sites

And what is the zinc/phosphorus levels of Rotella T6? Have heard a lot about zinc levels going down in diesel oils as well.

Share this post


Link to post
Share on other sites
1 hour ago, Last Indian said:

Question, in the same engine, running the same temperatures under the same loads using the same brand of oil which is better 10W30, 10W40 or 5W40?

I remember the late Pontiac historian John Sawruk was asked this question. His response was 10W30 was preferred over 10W40. He also recommended conventional oils over synthetics for stock or near-stock engines. BTW 10W40 oil works fine too.

John said the 10W30 was thinner, so cars with hard starting or residing in cold weather climates could to start easier. Since 10W30 and 10W40 were both spec'd for Pontiac engines back in the day, and not other formulas, he said stick with what works. He said to stay away from the 5Wxx oils as they were a thinner viscosity and Pontiac engines had such loose tolerances (as compared to today's modern LS engines) that thinner oils could get through these tolerances and cause leakage. Nor could they reap the benefits of a 5W weight oil since the last Pontiac V8 was built in 1980. 

Also, he recommended staying away from synthetics for similar reasons. Early on synthetics could cause leakage and seal swelling. The swelling issue has been largely fixed by oil OEMs by reformulating their oils. However an expense synthetic is not recommended for a stock Pontiac engine unless you have an engine builder who has tightened up the tolerances and recommends it. Besides why spend the extra money for no apparent benefit?

Edited by Frosty

Share this post


Link to post
Share on other sites

So, if synthetics are out, Amsoil and Rotella T6 are out because they are synthetic. So, of all the current-rated oils, what oil would you use if no synthetics and no access to older-rated oils? I'm not a fan of additives added to the oil.

Share this post


Link to post
Share on other sites
7 hours ago, vwalburn said:

And what is the zinc/phosphorus levels of Rotella T6? Have heard a lot about zinc levels going down in diesel oils as well.

Both Amsoil & Rotella T6 are 1000 ppm because they are synthetic. While Rotella T5  is a synthetic blend, part synthetic part conventional, which has 800 ppm, more than enough.

6 hours ago, Frosty said:

I remember the late Pontiac historian John Sawruk was asked this question. His response was 10W30 was preferred over 10W40. He also recommended conventional oils over synthetics for stock or near-stock engines. BTW 10W40 oil works fine too.

John said the 10W30 was thinner, so cars with hard starting or residing in cold weather climates could to start easier. Since 10W30 and 10W40 were both spec'd for Pontiac engines back in the day, and not other formulas, he said stick with what works. He said to stay away from the 5Wxx oils as they were a thinner viscosity and Pontiac engines had such loose tolerances (as compared to today's modern LS engines) that thinner oils could get through these tolerances and cause leakage. Nor could they reap the benefits of a 5W weight oil since the last Pontiac V8 was built in 1980. 

Also, he recommended staying away from synthetics for similar reasons. Early on synthetics could cause leakage and seal swelling. The swelling issue has been largely fixed by oil OEMs by reformulating their oils. However an expense synthetic is not recommended for a stock Pontiac engine unless you have an engine builder who has tightened up the tolerances and recommends it. Besides why spend the extra money for no apparent benefit?

Sorry Frosty, I meant it rhetorically, but your answer is correct. To expound on it further if I may? What I was getting at was, it depends on bearing clearance more than anything else, yes! My 302 Z was a loose engine for bearing clearance on purpose. I ran 20W50 racing oil. The 3600 Buick is a very tight motor so I run 5W30. Most people don’t have a clue about that issue or why you really run different weight oils.

You might find this of interest. About 15 years ago I presented a paper to our then VP over engine oils as to a theory on particulate in engine oil and it’s impact on oil viscosity in the bearing journal. He provided the money to run several test to prove or disprove the theory. It proved to be correct. As engine oil gets increasingly dirty by particulate or soot it starts to run into other particulate in the bearing area, elevating local bearing oil temperatures due to friction. This action causes the viscosity in the oil of the bearing area to decrease quite a bit. Thus this is one of my main reasons why I still change oil at 3000 miles. 

6 hours ago, vwalburn said:

So, if synthetics are out, Amsoil and Rotella T6 are out because they are synthetic. So, of all the current-rated oils, what oil would you use if no synthetics and no access to older-rated oils? I'm not a fan of additives added to the oil.

VW, if you don’t what to run the full synthetic oil, 1000 ppm Zinc, then consider the Shell Rotella T5 synthetic blend. 800 ppm Zinc, low ash, but still has some ash, which is good for the older motors as well.

Edited by Last Indian

Share this post


Link to post
Share on other sites

Last Indian, I do enjoy our back and forth discussions. I think we both learn something in the process.

So let me ask you this, do you recommend running an engine cleaner - in an attempt to clear all the sludge and carbon build-up - like you mention above - prior to a fresh oil change? If so, how often do you do it? Every oil change, ever other oil change? Every 10,000 miles?

Edited by Frosty

Share this post


Link to post
Share on other sites

Thanks for all the info guys! True, it has been a great exchange of data between you two. Oil has always been interesting to me; especially being in the aviation industry my whole career, starting as a jet engine mechanic. Looking forward to future discussions!

Share this post


Link to post
Share on other sites
1 hour ago, Frosty said:

Last Indian, I do enjoy our back and forth discussions. I think we both learn something in the process.

So let me ask you this, do you recommend running an engine cleaner - in an attempt to clear all the sludge and carbon build-up - like you mention above - prior to a fresh oil change? If so, how often do you do it? Every oil change, ever other oil change? Every 10,000 miles?

I enjoy our discussions as well, you’re a knowledgeable young man! 

No I don’t generally care for engine flushes. They reduce every needed oil component the engine needs to operate and be protected. While a multitude of folks use them without incident that doesn’t make them good. 

If I want to flush an engine I do so in the same manner we did or do at work, I use new oil and a new filter. Nothing, and I mean nothing cleans an engine better and safer than TBN, (total base number). If I still had access to my data and pictures of the testing I ran, and could show you the impact TBN has on an engine’s cleanliness and condition, it would blow you away, it’s that dramatic!

When I do flush an engine in this manner I drive the car for 100 miles and then do another complete oil change. If I feel the engine is exceptionally dirty, I’ll do a second flush with fresh oil and filter for another additional 100 miles.

For me now that is rare though, as I said before, it is rare for me to allow a oil change to even get to 3000 miles, which means when I change the oil the TBN is still higher than the TAN. Which means the oil was still in an active state of protection and cleaning.

My two cents worth, ok maybe three cents!

Edited by Last Indian

Share this post


Link to post
Share on other sites

Share this post


Link to post
Share on other sites

Great article Frosty! 

A littel further explanation. We have run a fleet test in Vegas taxi cabs for decades, so around 2008 a colleague and I had developed a product some 5 years earlier. We had a variation of it that we were considering for aftermarket and wanted to test it. The product was contained up in the valve train and slowly released over time increasing the total TBN of the oil in the engine. The results were awe inspiring! These motors had 130000 plus miles on them and the valve trains were needless to say a varnished mess. After running this product for one year of oil changes the valve trains weren’t just clean, they were bright metal again.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Recently Browsing   0 members

    No registered users viewing this page.

Tired of these Ads? Purchase Enhanced Membership today to remove them!
×

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.