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Are synthetic oils safe for your vintage engine?

It has been nearly five decades since consumers could first acquire synthetic lubricants engineered to suit specific needs of internal combustion engines. However, are synthetic engines oils all they are cracked up to be? And are they OK to use with a vintage car? Some "experts" will tell you synthetics are the cure for everything from oil consumption to leaks, but if that seems too good to be true it's for a simple reason: the reality is more complicated.


Read the article and watch the video over on 

Advanced Driver

This is a sales pitch for Mobil 1.  I've used that lube in a wide variety of high and low mile vehicles--including my lawn mowers--for ages with superb results.  That said, I price shop and buy a competitive synthetic if/when it's available at a significantly cheaper price.


Is "are synthetic engines oils all they are cracked up to be?" a bad pun?

Pit Crew

I have heard that going from a low detergent to a high detergent may cause the rings to start leaking.

As everyone loves high detergent oils it is hard to get an objective opinion.

Pit Crew

I use Castrol Syntec in our 1970 Karmann Ghia with a balanced and blueprinted 1.6l. You can't use it for break in of course, as the rings will never seat, but after a proper break in, it does great. I also use it in my daily driver which is a 338hp hot hatch, and when I pulled the head off for a precautionary head gasket swap at 190,000 miles, there was not even a wear ridge on the cylinders. 

New Driver

Seems there’s no specific reference to ‘Flat Tappet Cam’ engines, perhaps this is assumed. With air cooled vw engines this is a big concern requiring high zinc levels. I would like to know if there is a synthetic oil with low or no zinc and combine it with an anti friction additive so a catalytic converter can be added. I don’t want the  pollution coming out the back of my car, primarily for the environment but also for anyone driving behind me! I hate being stuck behind an old car getting gassed out!!! We need to change our ways to help the earth while enjoying our classics! I know there will always be those people that think they are too cool for school and run straight pipes, but most of us are more evolved and should find a better way!

Intermediate Driver

Mostly what I have read about synthetic oil has been good.

Mostly what I have seen and experienced about synthetic oil has been less than good.

I have tried it in my older cars and bikes, and gone back to conventional oil.

Synthetic seems to work fine in late model cars that were designed for it



I agree with you totally.  I've been using Mobil 1 since 1976 in every single engine I've owned including lawn mowers.  It was called Synthesized Engine Lubricant back then. I occasionally purchased Castrol SynTec if it was on sale but those are the only two I've used.   

And I have had no problems engine-wise from any of them.  


vintage flat tappet engines need zinc in the oil or you will wear out the camshaft. period. by vintage, i refer to virtually all standard production auto engines prior to the 1980's.

These older engines need certain additives which are no longer found in modern oils due to concerns for catalytic converters. Todays engines use roller tappets for reduced internal engine friction and slight improvements in mileage.


note that the last linked article indicates that there is ONE only synthetic which contains zinc. All the others do not. The oils they suggest can be hard to find. I found this stuff easily:


that is what I run in my 74 superior, 77 superior and my 47 plymouth coupe.


I fitted my Model A engine to less than .001, I use Mobil 1 5-20 but do add a half pint of 15-40 diesel oil, this puts in a little zinc but ... valve spring pressure is no 'biggie' anyway so little problem, there are no seals as such, I have no leaks whatever so looks like this thinner oil slings and drains back into the pan from rear main bearing better, there is almost no oil consumption at all.  No thermostat, engine temp is about 130 or 140 all the time, this synthetic is working for me ... runs like a very quiet clock.


Thank you, Kyle. My advice came from an old Wrench who said to me, do what makes you feel comfortable. There's no reason not to run Synthetics in your old cars. He was right. Frankly, I think I'm doing better with them. 


I have used Amsoil synthetic since 1982, I have used it in ALL my vehicles, classics and modern, it has always proved fine. I especially use 20w50 Racing oil in my older flat tappet cam cars because of the Zink. I have experienced several circumstances where the friction was greatly lowered reducing heat dramatically, highly recommend Synthetics, especially Amsoil.


No comments about zinc and the other components used in vintage car oils for flat tappet cams? It kills catalytic converts and was removed for that reason. Are synthetic oils capable for flat tappers without it?


I am interested in knowing about adding Zinc additives. I currently add ZDDPlus with each oil change. Believe it or not my 1971 TR6 engine doesn’t leak any oil (yet).
Pit Crew

I  would feel this is more credible if the engine examples shown were more than 10 years old, or included vintage components like a rope type crankshaft seal. Also unaddressed is the wear to flat tappets from modern oils, again the examples shown were roller units not subject to this problem. Also, my bet it that the target audience owns vehicles with a manufactures recommendation of 10W30 viscosity, not the 5W20 shown.

I'll keep searching.



Talking oil is like talking religion and politics to some. 

I still owning a flat tapper car and planning to own it for many more years I have a versed interest here. 

I dug into this with Mobil as that is the choice of my daily drivers. I did some research and found the racing version of Mobil One still has enough additives to be safe for flat tapper engines. It is what they recommend. 

Out side of that synthetic oil is a must use today as it is not that much more and holds much more ability to fight heat. In fact it is a must for any turbo applications. 

As for leaks you may see some more as synthetic oil has smaller molecules and can leak in areas the old Petro oil may not. Generally it is not enough to worry about but you may see a small amount more. 

As for Zinc if you want it you may need to move to a racing oil.


I get my Mobil 1 at Walmart as they carry the racing version of Mobil one at a good price.


My car is a mid engine so the use of synthetic oil to me is a no brainer. The added heat makes using a better oil a must.  



A minor point: My knowledge is decades old and therefore may be obsolete but I don't think oil ever leaks past exhaust valve guide seals into the chambers (as Jason mentions) since exhaust ports only see pressure, never vacuum like the intakes. When I was home building I didn't even use exhaust seals during assembly. It was never a problem.

Advanced Driver

I appreciate this article, Kyle!  Not only have you answered a couple of questions, but you have reinforced something I heard long ago regarding "particulate suspension--and filtration".   I will pass this on to my vintage club compatriots!  Keep up the good work!  jay salser

Pit Crew

Nowhere does he comment on synthetic oil content of friction reducers (ie: ZDDP) which we understand are necessary for older engines having flat tappet cams.

Pit Crew

Nowhere does he comment on synthetic oil content of friction reducers (ie: ZDDP) which we understand are necessary for older engines having flat tappet cams.


Folks lets get some facts in the way here vs just what we think.


The listing here has the parts per million zink and phosphorus. 

Don’t assume Diesel oils are safe as many no longer are. 

As for pollution out the tail pipe forget that. These additives are being removed as in new cars they can damage sensors and converters. On older cars that is not a factor and you also are not killing Bambi. 

I am using the 15-50 racing Mobil One that still has save levels for flat tapper cams. 

Like I said in my first post people like to argue oils like politics and religion. The difference with oils are they have specifications that removes opinion so no matter the brand learn what the numbers mean and what they are. Most MFGs show the specs on the oils and if contacted will offer a recommended oil.




Thanks for the link. As much as I would like to think it will shut down the debate, I......I'll just leave any further comments in my head.


Shell Rotella T conventional is 1200 ppm zinc and 1100 ppm phosphorous. I will stick with it.