Do you use conventional or synthetic motor oil in yo9uor squarebody?

[wazzabie]

Do you use conventional or synthetic motor oil in your squarebody?

[LT7A]

This was discussed fairly thoroughly about a month ago. I don't recall the name of the thread, but if you search for synthetic you'll probably find it. While I'm here though, I'll say that I am a fan of synthetic in my newer vehicles, but I won't be using it in my squarebodies until I have the motors out and update all of the gaskets. In my experience, the synthetic's ability to leak past the old gaskets is very evident. Has anybody had luck with synthetics having a formula to rejuvenate old gaskets and help them hold their seal?

[MJN]

I run AMSOIL Z-ROD 10w30 in my '74 K20. No leaks, doesn't use any oil, no issues. I also broke in the engine with AMSOIL SAE 30 Break in oil.

[wazzabie]

I still have cases of older motor oil... before the Energy Conserving label. I think it may have more zinc then todays motor oils.

[Nick_R_23]

Synthetic in everything. Synthetics causing leaks is a long disproven myth.

[cadillac_al]

It's not disproven at all. It cleans the gunk off your seals better than conventional oil and flows out past the seal better than conventional oil. It is superior oil that can find it's way our of an old engine.

[kwmech]

Originally Posted by wazzabie

I still have cases of older motor oil... before the Energy Conserving label. I think it may have more zinc then todays motor oils.

Ditto, I've probably got about 200 quarts of different weights and about a dozen or more 5 gal pails of 15/40, 90wt and atf left over from my gas station sitting in my storage shed. Still working my way through it. Straight 30 wt, 20/50, 10/40, 10/30, . The heavier weights have been sitting for over 20 years still sealed in the cardboard boxes. They don't get used much like they did back in the '90s

[truckin 79]

I have switched back and forth from conventional to synthetic. This trip around I am using Walmart synthetic 10w-30 and it seems to leak less and is why I switched back to synthetic. My engine needs a rebuild in the future so I am going to go with 15w-30 next oil change with synthetic. Synthetic is almost as cheap as conventional oil and everything I have read is superior to conventional oil.

[Gotenntitans]

Valvoline 10W30 in the '87 and Pennzoil 10W30 in the '90. Always heard it was best to keep using the original brand in the engine that was in it when new so that's what I do. No issues with either.

[Nick_R_23]

Originally Posted by cadillac_al

It's not disproven at all. It cleans the gunk off your seals better than conventional oil and flows out past the seal better than conventional oil. It is superior oil that can find it's way our of an old engine.

This is false. Synthetics do not cause leaks.

[LT7A]

Originally Posted by Nick_R_23

This is false. Synthetics do not cause leaks.

Sorry man, it doesn't matter how many times you say that, it's not going to convince those of us who have experienced it. Feel free to post up your information source on this and I'm glad that synthetics have worked unfailingly for you. I respect your knowledge on many things, but it can't be disproven when you've personally experienced it first hand. I'm not going to debate the semantics with you of whether or not synthetics actually cause leaks or just leak more in a given situation. The bottom line is, in my experience, more oil comes out through the old conventional gaskets with synthetics. I have a truck that I've owned since new, switched to synthetic, and watched the gaskets start to leak within weeks.

[Nick_R_23]

It is indeed a myth. Just like the myth of breaking in an engine with conventional oil before switching to synthetics. Sources: Actual oil engineers.

https://www.mobil.com/en/sap/persona...out-synthetics

Mobil 1 does not cause leaks. In fact, new Mobil 1 was tested in dozens of industry standard and original equipment manufacturers (OEMs) tests to prove its seal performance. It is fully compatible with the elastomeric materials from which automotive seals and gaskets are made. If an older engine is in good condition and does not have oil leaks, Mobil 1 provides the same advantages as it does when used in a new engine. ExxonMobil recommends taking measures to repair the leaks before using Mobil 1. ExxonMobil also recommends following the automobile manufacturer's manual for the proper oil to use.

http://ultimatesyntheticoil.com/oil-...-synthetic-oil

A far more common result of changing to a true synthetic motor oil is to eliminate oil-seal leaks. In fact, AMSOIL synthetics are rigorously designed to be not only compatible, but even MORE beneficial to seal materials than conventional oils

https://www.cenex.com/about/cenex-in...gine-oil-myths

This is an often-cited myth. In fact, if your seals and gaskets are in good condition, synthetic oil will not leak in your engine. Synthetic oil has not been shown to deteriorate engine seals or gaskets

https://www.midas.com/auto-repair-se...tic-oil-change

Synthetic oil does not cause leaks, but you may notice an existing leak after your first synthetic oil change. That’s because synthetic oil can clear away conventional oil build-up that was plugging an existing leak.

https://www.pennzoil.com/en_us/educa...hetic-oil.html

The myth is rooted in the idea that synthetic oil is “slipperier”—lower in viscosity, or not as compatible with seals and will therefore leak or leak more in places conventional oil might not. Again, completely untrue. Synthetic oils will enhance the engine protection in older vehicles with higher mileage, just as they do for new engines.

The only small bit of claim to truth that myth has, is that synthetics do tend to contain a higher concentration of detergents that are more effective in cleaning engine internals - including deposits left on components that house a sealing surface. But, that’s where a lot of false information begins. The truth is, these deposits are caused by inferior conventional oils. These deposits will starve the seal from lubrication, conditioning additives, and the cooling effect provided by the oil, causing seals to dry, overheat, or lose elasticity. So in reality, it’s actually the conventional oil that causes a seal failure. In addition, synthetics also contain seal conditioner additives that not only maintain, but can restore seal functionality. That’s right - synthetics actually work to prevent leaks. The longer the usage, the longer the time the additives can work to improve a seal’s performance. This is also why the stories of “I put synthetic in and it leaked and put conventional back in and the leak immediately stopped” are nothing but pure BS - for one, the detergents don’t clean out deposits instantaneously, and two, once the deposits are removed, they don’t immediately get replaced when switching back to conventional.

[LT7A]

Thanks. I appreciate your thoroughness. There are a couple of things in there that back up my and probably others' experience. First of all, many of us don't have elastomeric gaskets in our engines. Second, it cites the possibility that it cleans out conventional oil deposits that are helping keep oil from leaking past the seals. So once again, does synthetic oil cause leaks? Semantically, maybe not. Will you see more oil coming through your gaskets if you switch to synthetic oil on an older engine? You might - I sure did. And on one that was sealed from the factory with less than 25,000 miles and less than 1 year in operation. To be fair, I consider amsoil to be a very good product and maybe their seal conditioners truly do work. Hard for me to step up to that cost on an old motor. Mobile one sure finds its way through the gaskets though. And they don't claim that it won't leak on old style gaskets. So the use of the word myth is by companies that want to sell their product and is far too broad. By placing parameters on the conditions of its usage, they tacitly admit that if your engine doesn't meet those conditions, that you may see the oil coming through.

[Nick_R_23]

Are you talking gasket or seal leaks here? Your post is intermixing the two, but they are completely different styles of sealing. A gasket is a gasket - the material that gaskets are made from are impervious to oils, regardless of conventional or synthetic. Oil type makes no difference on the effectiveness of a gasket. The only way a gasket can leak is through a defect or imperfection of a sealing surface (gasket damaged or manufacturing defect, sealing surface damaged, or not flat or machined correctly), or if the clamping mechanisms are improper (bolts spaced too far apart for even clamping distribution, bolts too loose, bolts too tight causing fasteners to yield and provide inconsistent clamping force or warped sealing surface). By design, oil cannot physically make its way past a gasket unless there is a mechanical defect or failure allowing it to do so. Oil cannot cause any gasket related sealing failures.

[farmall]

Synthetics leak on older engines because they work better in every aspect of lubrication. If it flows better it will make a seep act like a leak.

[cadillac_al]

The engineers probably think an old engine is 5 years old not 20+ years old. I used to run Mobil 1 in everything. I slowly moved away from it because I hate oil leaks with a passion. When my Acura started leaking that was the last straw. I still use it in my Honda motorcycle because it has to deal with extreme heat and Hondas never leak. In American cast iron engines I'll stick with conventional. All my vehicles wear out before the engine does anyway. I sell used auto parts and all my parts vehicles have good running engines in them. I really don't need them to last any longer than they already do. Just my .02

[LT7A]

Originally Posted by Nick_R_23

Are you talking gasket or seal leaks here? Your post is intermixing the two, but they are completely different styles of sealing. A gasket is a gasket - the material that gaskets are made from are impervious to oils, regardless of conventional or synthetic. Oil type makes no difference on the effectiveness of a gasket. The only way a gasket can leak is through a defect or imperfection of a sealing surface (gasket damaged or manufacturing defect, sealing surface damaged, or not flat or machined correctly), or if the clamping mechanisms are improper (bolts spaced too far apart for even clamping distribution, bolts too loose, bolts too tight causing fasteners to yield and provide inconsistent clamping force or warped sealing surface). By design, oil cannot physically make its way past a gasket unless there is a mechanical defect or failure allowing it to do so. Oil cannot cause any gasket related sealing failures.

Once again, I respect your knowledge. But I have a much simpler perspective on it just based on my experience. Gaskets are part of what is used to seal an engine so when I say seals I'm including gaskets. As you noted, gaskets fail for a number of reasons. Synthetic oil does a better job of finding and exploiting those failure points. And with that said, I will end my communication on this. I'm pretty straightforward in how I think. Personal experience speaks louder than anything I'm led to believe, especially by those who have something to gain by convincing me to buy their product, although I appreciate the links and quotes you posted. At this point, I've more than made my point and done my best to address the question of the original poster.

[jocko]

Synthetic oil doesn’t “cause leaks” per se - however, since today’s synthetics are generally lower viscosity than the conventional oils we use most of the time in these old trucks - it is more likely to seep past a flawed gasket than a higher viscosity conventional. Apples to apples though, a 5W30 synthetic and a 5W30 conventional should behave about the same around the same flawed gasket. In other words - I believe it is more a question of viscosity than conventional vs synthetic.

[sweetk30]

Mobil 1 5w-30 in my new gm long block L31 in my square .

01 3500-hd with 8.1L gets mobile 1 truck & suv oil for more heavy duty use .

[richards72chevy]

Do they make a synthetic that contains zddp?

[THI]

Originally Posted by richards72chevy

Do they make a synthetic that contains zddp?

AmsOil Z-Rod

[MJN]

Originally Posted by richards72chevy

Do they make a synthetic that contains zddp?

AMSOIL Z-Rod was already mentioned- that is what I use in my trucks. AMSOIL Premium Protection 10w40 (AMO) also contains higher levels of zinc https://www.amsoil.com/p/premium-pro...motor-oil-amo/
Both are great options for flat tappet cam engines.

Some good information available here: https://blog.amsoil.com/synthetic-vs...-in-older-cars

[blazer2007]

I use Lucas hot rod oil in mine and was told I could use Syn. if I want to after break in period, as it is a new motor

[72c20customcamper]

I've been using this in all my flat tappet engines. As replace I go with roller cans so any good oil works well .

The amount I drive most of them synthetic is to expensive . Some get only a few hundred miles a year

[Greenlee]

After rebuilding my truck with a 350 TBI crate motor about 10 years ago I have been using synthetic the entire time. Usually Mobil 1 or Royal Purple 5w30. Did not realize there was anything controversial about using it. No leaks to speak of. I did have a leak around the oil filter a couple times. I try not to over tighten it but maybe didn’t get it tight enough.