1999corvettels1

I've only run synthetic in my LS1 in the 1999 Corvette, Mobile 1 5-30 full synthetic as the oil cap on engine says, but on older vehicles and other modern daily driver's (4 cylinders) I have just used regular oil.

Have heard swapping to synthetic causes oil leaks.

Does anyone here run full synthetic in old (pre fuel injection era) engines?

ignatz

I would suggest you stick with what works. I wiped a fuel pump lobe when I switched to Mobil 1 synthetic. Go do some research on zinc additives.

Batty Mantis

There is a sticky at the beginning of this section with a list of flat tappet oils

HeadsU.P.

If the dead horse gets beatin' anymore there will be nothing left but skin & bones.

Diablozx9

I use Mobile 1 full synthetic in my 350 SBC.
I dont need to hear from anyone who doesn't agree with my decision, I am only answering the question asked.

Jebbysan

Jebby

jb78L-82

Synthetic oils do not cause leaks, bad gasket cause leaks. Make sure the oil you use has the proper ZDDP zinc additive and you are good to go. I ran Mobil 1 oil in my OEM L-82 from 1985 to 2014 with zero oil issues running a flat tappet OEM L-82 cam and OEM fuel pump, when I did a complete rebuild/upgrade in 2014. If you decide to use a Mobil 1 oil, I would run 0W-40 European formula or better, Mobil 1 15W-50, made specifically for flat tappet cam motors.

cv67

I prefer an oil with good sheer strength/cushion effect with old school stuff, it isnt Mobil syn thats for sure.
Tomorrow everyone can argue about whats best, along with resale value.

ive run both in ls engines it doesnt matter really...dino oil will quiet down noisy lifters they are known for .

jackson

I don't, but ...
Run whatever floats your boat ... no matter what oil ... no matter what practical experience someone has with it ... there's always some argument against it ... may as well be herding cats.

Batty Mantis

I agree for the most part. You can run anything if have a roller cam. If you have a flat tappet cam I recommend either using oil containing ZDDP, or using an additive like Lucas TB Zinc-Plus in whatever oil you prefer. Regular oil changes are always the most important thing. My understanding of synthetics are that the molecules are smaller. Supposedly that is the reason you can go longer between oil changes. I personally prefer dino oil. I always change my oil every 3000mi. or less regardless.

1999corvettels1

Will have to research what oils have that already in it, and not put in synthetic in.

Lakeside49

You really can't go wrong with today's brand name modern engine oils. Our company (Ford) led the OEMs in oil quality standardization in the mid-1980's (Dennis Groh, Senior Ford/Motorcraft lubricants engineer). Every other OEM, and quality aftermarket oil producer was grateful for our taking the lead and enthusiastically worked together in an unprecedented manner because it was a win-win all around. One thing that spurred it was an engine oil sludging problem in one of our modernized, lean-burn (efficient/hotter) engines. (Toyota re-experienced it more severely over a decade or so ago resulting in lawsuits/a massive recall). It was awful when it happened to some our customers. After extensive testing the problem was traced to one major engine oil producer. A TSB was immediately published to our Dealers addressing the issue - followed by a lawsuit by the major producer claiming defamation and Ford lost the suit despite the test data; in part because the producer was not deemed negligent as claimed since there were no standards to claim breach. So, they paid the producer (yellow bottles, let’s drop it at that) but Ford then proceeded to lead the way for standardization and industry certification as identified by a compliance seal printed on the bottle of participating companies. As an aside, all engine oils are basically 80% base stock and 20% "proprietary secret sauce" (i.e. anti-foaming agent, detergent, viscosity agents, particulate suspension, friction coefficient modifiers, anti-oxidation, et al).
Regarding the seal-leaking causal rumor, early synthetics purportedly did not have whatever petroleum distillate that naturally swells seals - so, it had more to do with the lack of swelling in older seals than the other baseless myths that were rumored. I believe that was long ago remedied by both, the seal manufacturers and oil companies.
Regarding the "conventional vs synthetic" debate, again today's certified (only) lubricants are truly superb (including yellow bottles). But, the industry durability test data that is consistently released right down to the molecular level on synthetic lubricants (all of it, 100%, zero exception - period, end of debate) demonstrates significantly superior anti-friction and wear performance over time. Mr. Groh explained that, in my over-simplified/paraphrased form here, that all (100%) oils have a "sheer point" where the oil film that separates two moving parts under sufficient stress. Picture piston rings cutting through their lubricating film on the down-stroke...or, a crankshaft semi-floating on a microscopic film of oil around the main engine bearings. The difference between the conventional oil and synthetic oil is that the tiny lubricating molecules in synthetic oil are extremely uniform in size (envision millions of microscopic ball bearings all the same, optimal size) vs. conventional oil whose molecules vary. Most of them are a perfectly suitable size and consistently doing a stellar job - but... a few of them are too small, thus slightly and temporarily underperforming the shear point whereby the moving metal can microscopically knick off a couple of extra metal molecules that its synthetic sister probably wouldn't have experienced - at least not quite as often. It is completely unnoticeable except under a microscope - but, over an extended period of time those "knicked-off" micro-particles can add up. I'm told this explains the clear industry test data - and, why there are so many stories of engines breaking the 400k+ miles barrier - and, why synthetic lubricants are prescribed by some OEMs, particularly the Germans (who greatly advanced the science of synthetic fuels/lubes during WWII out of necessity) despite its cost penalty. That said, synthetic oil is still relatively expensive -especially with the extra markup at some of the fastlube places - and should remain a personal decision given the good performance of today's certified conventional oils. What’s a few extra wear molecules between good forum friends.

Hoping this helps others - as well as answering the O/P’s question.
DV

jb78L-82

Cannot thank you enough for this knowledgeable explanation! Thank You!

I do have one question since you said all oil is basically 80% stock? In The US only, synthetic oils are allowed to be called "synthetic" even though most are highly refined dino oil only, Group III...the oil lawsuit way back. However, a true synthetic is a group IV PAO ester not a group 3 highly refined dino oil as allowed in the US. There are some group IV synthetics in the US but most are really just Group 3's in the US only? Also, Penzoil Platinum is made from Natural gas, so does that oil qualify having a different base stock as well?

Maybe finally some of the nonsense about synthetics can finally be put to rest.:

Please correct any of the following summary about synthetics versus conventional oil:

1. Synthetic oil clearly is superior to conventional oil in protecting metal to metal parts contact in an engine since the molecules are not only smaller than conventional oil but more importantly, uniform in size.

2. The synthetic oil seal leak issue was resolved many years ago by both the oil companies and seal manufacturers...non issue for the last 25 many years.

C6_Racer_X

This could be a "distinction without a difference," but synthetic oil doesn't cause leaks. What it does is clean the dried gunk out of leaks you already had.

Older seals can have cracks in them. When conventional oil seeps out, it oxidizes when it gets to the air and forms a thick, tarry, sticky substance. That usually doesn't drip out, and it sort of seals the leak.

Synthetic oils usually have more detergents in the additives package, and they tend to clean out the gunk. And then, synthetic oil flows better than conventional, so when the leak is cleaned out, it flows through the cracks/leaks and drips on the ground.

I run synthetic in any engine I've replaced all the gaskets and seals in.

Others have mentioned the Zinc issue, and with slider cams, you either need a truly high zinc oil or you need a zinc additive to get enough ZDDP in the thing to keep the cam from wearing out. In the past 10 years, I've replaced a lot of camshafts in older engines when they come in with flattened lobes. Unless you like replacing camshafts (and have a good supply of camshafts available), you need higher ZDDP levels than most modern oils offer. On the Chevy engines, it's mostly just extra work and an annoyance. On Mercedes Benz M117 engines, the camshafts are over $500 each and there's two of them, so it's a bigger deal with those. On VW and Audi engines, some of those cams are getting really hard to find at any price.

I send oil samples in to Blackstone periodically, and I look for 1200ppm Zinc on the oil I'm draining at an oil change. Most PennGrade 1 oils hit that for me, and RedLine Racing oils work as well. Anything else I've tried needs additional zinc to hit that target.

jb78L-82

Mobil 1 15W-50 has 1200 PPM ZDDP listed on Mobil's website which is why I used it for years in the OEM L-82....................L-82 camshaft looked brand new at the engine teardown in 2014..........zero wear

BTW-My experience across a vast array of engine types is that if a gasket is capable of a leak, regardless of whether a conventional or synthetic oil is being used, the oil will leak just slightly less with a conventional oil versus a synthetic. In my experience, a conventional oils which are also all highly detergent today will not prevent or manifest a leak, if the gasket is weak..............with any oil today.....

C6_Racer_X

Which is why I don't run it in my Mercedes Benz or VW/Audi engines. And I wouldn't recommend it for any engine with a slider cam. I wiped out both cams on a 5.6L Mercedes Benz engine with "Valvoline racing High Zinc" oil after they dropped that formulation to only 1200ppm zinc.

To be clear, when I drain the oil, I send a sample of what's coming out of the engine for analysis. That's when I want 1200ppm of Zinc in the oil if it's got slider cam(s). If it starts at 1200ppm, it's not going to be there after a full service interval.

The stuff I use is generally over 1550 ppm Zinc when I start, and in the 1250-1300ppm range when I'm draining it. That's for a 3000 mile oil change interval.

If I extend that with synthetic oil, I add even more zinc, or I add another bottle of zinc additive when I change the filter (but not the oil) every 3,000 miles if I'm running 6,000 or 9,000 mile oil change intervals with the synthetic oil. I have done that on one of the old VWs back when I drove it daily.

jb78L-82

Understood..makes sense....you are looking for 1200+ PPM ZDDP at 3,000 miles when drained.

With all my roller motors I go 5,000 using synthetic but ONLY Mobil 1 0W-40 or Castrol Edge 0W-40 European Formula Only (Mercedez, Audi, BMW VW approved)........2001 GM V6 3.1 currently at 220,000 miles with zero oil consumption and 3.5L Chrysler V6 double Overhead cams with 160,000 miles with zero oil consumption.........

pd64

I run Amsoil Z-Rod 10W-30 in my 1976 L82. It contains 1440 ppm Zinc

71 Vert LS1

I worked for the packing industry for over 36 years and our company supplied over 50 packaging machines when the oil changed from 1 quart fiber cans to the plastic bottles we have today. I spent a lot of time building, installing and then later selling these machines.
Big companies like Mobil typically only make oil with their brand name. But other large companies like Valvoline market their own brand but also "co-pack" for many brands like Oreilly's, Autozone Wal Mart and many others. There are also oil packing companies that don't have brand name and only co-pack for other companies.
As said above the base oil stock comes into the plant on a rail car or if near a port on barges. It's processed at the plant and the brands "secret sauce" of additives is added to the base stock. Many times the oil going to the different stores with their brand is exactly the same formula as the other stores. Only the bottle color or shape and the label on the bottle change. So some people swear by a certain brand and it could be exactly the same formula as a brand they think is junk.
Many times when talking to the Mobil plant guys they would ask me how often I changed oil. I always used Mobil One in my daily driver. I said 5000-6000 miles. Without exception they said I was throwing away good oil and could easily go 8000-10000 miles depending on my driving style and conditions.
All my hot rods for the last 15-20 years have had roller cams so its been Mobil One in all of them. If it's new engine build my engine builder likes to break them in on the dyno with dino oil and then switch over to synthetic.

7T1vette

Full synthetic oils provide so much better engine life than dino oils, you would be foolish not to use them in classic car engines. You can figure out how much 'zinc' you need in your engine and use an additive, if you need it. Molecular size of full synthetic oils is much smaller than dino oils, so it will weep thru smaller openings in worn seals & gaskets. That is why folks say that synthetic oil "causes" leaks. In fact, its your seals and/or gaskets that need replacing due to long-term wear. All [good quality and properly installed] seals and gaskets, which are in decent condition, will seal ALL lubricants from leakage.