Synthetics and Seal Leaks

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Sep 6, 2002
Cordova, TN
In the additives section, Frank has asserted that synthetics degrade seals and contribute to or casuse seal leaks while dino chemistry does not. JB also has a post there asking about this in more technical terms but no one has replied. I thought I'd raise the issue in the main forum. Do today's synthetics, synthetic blends and high milege dino oils containing esters promote seal degradation and oil leaks. I'd be interested in knowing what the experts have to say on this.
I have used Mobil 1 on the last 4 cars (Honda Accord, Toyota MR2, Nissan Maxima, Volvo S60 T5), with an OCI between 7K and 10K. All cars, except the Volvo, were kept for 7+ years and saw well over 100K miles. Never had an oil leak, never had to add make up oil between changes.
My wife's '92 Mercury Sable has had synthetic oil since new in July '92. No leaks. 88K miles. Yes, it's low mileage, but the oil is still in the engine and if it was destined to leak because of synthetic oil, it would.

We run about 4-5 tanks of gas per year or about a 1000 miles per year.

Cheers, Doug
My BS detector went to condition orange on that one.

1991 Honda Accord, 185,000 miles when sold to MIL, 205,000 miles now, still no leaks
1995 GMC Sonoma 96,000 no leaks
2000 Acura 3.2 TL 81,000 miles no leaks.

What do these vehicles all have in common?
M1 since the first oil change.

Other people I know with high mileage vehicles run on synthetic don't seem to have any unusual leakage problems either.

My impression, which is no more valid that the original assertation that synthetics cause leaks, is just the opposite. It seems to me that vehicles run on synthetics have fewer leaks.
The whole synthetics-cause-leaks debate goes back to the 1970s. Perhaps an old-school way of looking at synthetic oils, but I don't buy it.

I wish someone can put proof on the table that modern synthetic oils cause leaks. Until then....When will this debate ever end?
Hmmmm... I have a '97 Chevy S10 with the 4.3L V6. It was run the first 93K with dino oils and recently switched to synthetics. First the Supertech synthetic, then the Texaco Havoline Synthetic found at Big Lots for $1.99/qt. So far, not one single leak and I'm at nearly 102K. The next change will be with either Mobil 1 or Amsoil. I used the cheaper synthetics the first two changes to be sure it was flushed well before putting in the expensive stuff.
No...synthetics certainly do not degrade seals. Anyone who says that doesn't know much about today's synthetics. What they do is clean the seals (and everything else) causing leaks to happen that were once filled with sludge. This is why engines that have synthetics from the start don't start leaking as much as it would if you had used dino oil for the last 100,000 miles.
If the engine is past 100k miles, chances are the seals are hard and brittle. any oil will get past them. Synthetics might leak at a faster rate though. I switched to Mobil-1 on a older Scirocco and couple months later the crank seal leaked taking out the clutch disc. After replacing the seal and clutch, no more leaks.
I forget where I read this, but dino oil has a natural property of swelling some types of seals. Synthetic oil does not. Esters are added to synthetic oil to establish the same seal swelling properties of dino oil.
There were some problems with early synthetic oils. Also, prior to about 1980, some vehicles had seals that were not compatible with the new synthetic oils. And if a vehicle is driven 100,000 miles or more using conventional oils, and then synthetic oil is used, sometimes leaks develop because the synthetic oil removes false seals made up or sludge on the seals. All modern synthetic oils are supposed to be fully compatible with seals used in vehicles at least since 1980.

I think it is a good idea to clean an engine every 25,000 miles or so with Auto-RX. That way, the seals will stay clean and pliable.
The reason I asked this is because Frank freq. tells people to avoid synthetics. He often cites the synthetic ester as the proably cause of the seal leak to begine with. He goes on to say that once fixed with AUto-Rx not to ever return to synthetics or the leak will reoccur.

I do not have a problem with him saying this as it might very well be true. I am not a chemist or tribologist. I was always told though that the seal swell or lack of it issues had been resolved in the 1970's. If their is anything I need to know about synthetic ester I want to know! I happen to use one of the highest ester content oils made in N.America so it of concern to me.

I have used synthetics for a long time and have never had a problem but better to safe then sorry!

P.S. See my origanal post under addtives section it little past half way down last time I looked.
I have read all the points folks have made here many times before but why is Frank, who is obviously a pretty smart guy, convinced that synthetics cause seal leak? Also, why does he say, sometimes, that a maintenance does of 3 oz added to the synthetic oil will prevent this degradation?

Heck, if this is true, I think Frank could make more money off ARX by relabeling it SealRX and also selling to all the people that use synthetics, synthetic blends an high-milege dinos with esters so their seals don't leak down the road.
The reason he says this is because he want's you to continue using dino oil that will continue to get your engine dirty so you will continue to buy his product.
Either that or he just doesn't know that he is wrong, but I sure hope not given the product that he sells...
I want to make it clear that my intentions were not to make this into a Frank is wrong lets get him thread!

I sincerly want to understand how this is supposed to happen. I plan on getting 300,000 miles out of my Toyota Camry and I would rather have the seals last as long as possable. Just because I used to work on cars for a liveing does not mean I ever liked it. Their is a difference at being great at something and enjoying it!!!

I also enjoy my amature tribology hobby!!
I have a Cadillac STS with a small oil leak in the timing chain cover. With dino oil there is oil on the bottom of the car but not a drop on the floor. With any syn. oil there is a big leak in the car with a puddle on the floor . I do not believe syn. cause leaks but I do believe the very nature of the oil makes an exsisting leak much worst. Interesting enough valvoline max-life seems to be the one that works the best--the one that seems to be liked the least on the form. Roger
In three used cars purchased with 30,000 to 60,000 miles on them all three developed seal leaks within the first year of conversion to Amsoil. Now, around 120,000 on my Camry (synthetic since birth) it developed at least one seal leak now 161,000 miles. Obviously not worth repairing until a timing belt is due. I am currently trying the RX treatment though.

For me the question (leaks and synthetics) remains up in the air but I keep using synthetics. As to Frank, not sure exactly where he is coming from but RX does need to produce some final instructions on the use of that product for cleaning, seal leaks etc. His statement does contradict what his own instructions state.
Roger3116 speaks true. If your car leaks with dino oil, it will leak faster with synthetics.

Awhile back I challenged Frank to explain EXACTLY why synthetic oils are allegedly harder on engine seals. The explanation didn't come.

The bottom line: In 2004 modern synthetic oils are NOT harder on seals. In fact they are much better for your seals than petroleum oils that have a relatively high percent of pour point agents. These lower cost oils have solvents which, over time, will dry up seals and the oils themselves will leave deposits which are abrasive to seals.

I, of course, have many years on synthetics. My cars don't leak (one has 242K miles).
Esters promote elastomeric material seal swelling. Frank says AutoRx has esters. PAO-based synthetic oils also contain esters. High mileage petroleum oils contain esters. Frank says AutoRx solves leakage problems. High mileage petroleum oils solve leakage problems. Frank says PAO-based synthetic oils cause oil leakage? Am I missing something here?
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