Synthetic oil in long stroke motors

[Rusty_OToole]

Has anyone used synthetic oil in a pre 1955 long stroke engine. I am thinking specifically of a 1951 DeSoto and 1954 Packard but could be any typical motor of the 30s to early 50s.

It seems to me the synthetic should work particularly well in this type car because the long stroke causes higher piston speeds, more friction and wear than modern short stroke engines.

Assume the engine will be freshly rebuilt or overhauled, and all sludge and dirt cleaned out.

[Guest Oldengineer]

When I bought my 48 Chevrolet, the PO indicated that the engine had been recently rebuilt, and it had synthetic oil in it. The problem I had - was the synthetic intensified the amount of oil that leaked through the old rope seal that the Chevy 216 uses for its rear main seal. Everytime I shut the engine down I'd have a large puddle of oil under it. I switched to Castrol High Mileage oil and now she only leaks perhaps a teaspoon full of oil on shutdown. Guess my caveat is - if the vintage engine has a propensity to leak oil somewhere because of its design, then, the synthetic oil will probably make it worse.

Regards:

Oldengineer

[NTX5467]

The other thing is the compatibility of the existing/replacement seals with synthetic oil. With time, some formulations of synthetic motor oil or transmission oil can soften the rubber seals and let them become "degraded". I saw that in reference to a particular manufacturer not going "full-syn" on their upgraded automataic trans fluid, for that reason.

Somewhere, about 2003, there was a thread on this subject in the Buick forums. At that time, a contingency of Buick owners were driving their Buicks from Washington state. Some used Amsoil synthetic motor oil, as they noted. No problems with leaks or seals, they said. You might see if you can find that as there were some very good comments in there, back then, on this subject.

Years ago, a friend started using Castrol GTX in his SuperBee's 383. He knew it was good oil, but cussed it because he now had "oil leaks everywhere". He changed back to Pennzoil and the leaks stopped. Therefore, Pennzoil was better oil than Castrol. I used GTX 20W-50 in my cars with NO leak issues, though.

What's probably happened with the Chevy 216 is that in the area of the crank where the rope seal "seals", with miles, there is some wear on that area from contact with the rope seal. Obviously, the new seal didn't compensate for that. If it'd been a lip seal, it would be very obvious. This is why some replacement lip seals move the seal around in the housing to put the lip on an un-worn piece of the shaft it's going to seal. Like .045" one way or the other. Of course, on the front end, there are the "sleeves" for this function.

It used to be that synthetic oil was not recommended for "new" motors, as it allegedly was too slick for the rings to seat. So you ran normal oil until the first oil change and then put the syn oil in it. I'm not sure if that recommendation still exists, though.

The side loading on the piston skirts is not particularly related to the longer stroke, but to the relationship of the ctr-to-ctr length of the connecting rod to the stroke length. I suspect the Chevy small block 400 V-8 has a lower "rod ratio" than your DeSoto or Packard might . . . even with its shorter 3.75" stroke. The longer stroke would certainly affect "piston speed", but at the <4000rpm levels the referenced motors usually run in, not a real big consideration.

On your (hopefully) OEM-spec rebuild, I think I'd first use normal 30 viscosity motor oil, which you can still find at WalMart in Pennzoil or similar brands. Run it about 2000 miles or so to get everything seated-in. Then change it with the same oil and see how that goes. That should give you a decent baseline on performance and oil consumption, too. Then you might branch out, at the next oil change, with a 10W-30 or 10W-40 multi-weight oil, to see how the oil pressure might be, plus leaks/consumption.

I have deliberately NOT mentioned the zddp issue. Reason is that those earlier motor oils didn't have that much of it in them, anyway, I suspect, as there was no real need for it. Low-lift camshaft, weaker valve springs, slower engine speeds . . . generally. BUT I recently found a QuakerState "DEFY" motor oil at WalMart with an "SL" service rating . . . the service rating BEFORE all of the emission things started needing less of this or that in their formulations for emissions hardware longevity and performance. Plus, almost every camshaft maker now has their own zddp additives they sell, plus some other brands, too. BUT if you can find some 10W-30 Rotella T, even the normal 15W-40 viscosity rating, then it'll have more than enough zddp in it already. Plus, being readily available.

Rotella, as Castrol, now has blended syn oils, too, which might be a consideration. Or if you like Castrol, they have some GTX Diesel oil, too.

To me, though, IF you re-used the original camshaft and keep the current valve lilfters in order when you remove them, to reassemble them onto the same camshaft lobes, the issue of zddp might not be that critical as the bulk of the camshaft/lifter "wear-in" has already happened. The interesting thing about the DEFY motor oil is their claim that it'll prevent up to 98% (as I recall) for future engine wear.

You can head over to www.bobistheoilguy.com and look for "Virgin Oil Analysis". In that part of the website, you'll find chemical analysis of motor oils done by labs that do those things. It'll list the amount of the particular "things" in the motor oil, including the "zinc" level of these new, unused motor oils. Lookin' is free, but posting needs a registration and password "membership".

If it was mine, I'd do the initial time on normal straight-weight 30 motor oil, liberally pouring some GM EOS supplement over the cam and lifters when the engine is assembled and before it's started. Then continue as I outlined above. To me, that'd be a good way to ensure no surprised happened before "fancy" motor oils were introduced to the oil pan.

Just some thoughts,

NTX5467

[Matt Harwood]

I use synthetic in all my cars, old and new. I don't get hung up on the zinc hysteria and its mostly anecdotal evidence, but the benefits of synthetic are well-proven and should serve any of these old, low-RPM engines very well. I'm of the contingent that believes in synthetic because it clings to metal better (more oil on moving parts at start-up), because it flows better cold, and because it is more stable at higher temperatures. I've noticed that my 1929 Cadillac gets oil pressure almost immediately at start-up, runs right about 30 PSI oil pressure even after a long, hot day of touring, idles at about 12 PSI hot (which is exactly where the manual says it should be) so it's working as it should. I've used it in my race cars without ever having a mechanical failure, and in my turbocharged cars, one of which has two turbos and is now over 100,000 miles with nothing more than oil changes and a timing belt replacement as [preventive] maintenance.

The thing about leaks and synthetics isn't that they're causing old seals and gaskets to fail, it's that the synthetic oil molecule is different than the regular oil molecule. Instead of clusters of carbon atoms as in regular oil, synthetic has long chains of molecules that can fit into smaller openings and slide past each other more easily (hence the better lubrication properties). But those same molecules will find their way through holes through which regular oil molecules can't fit. So while some guys use their anecdotal experience with some synthetic oils as proof that it causes leaks, the real reason is that the holes are still there, it's just that one oil can fit through them and another one can't.

For me, synthetic oil is cheap peace of mind. Well, at $7/quart it's not exactly cheap, but I only change the oil once a year in the old cars and about 4 times a year in my daily driver, so it's not a massive expenditure given the many proven benefits. If you have a fresh rebuild with modern gasket materials, I would think that you won't have issues with leakage. Rope seals and cork gaskets may see some seepage, however, but this is not evidence of failure. You might experiment with different brands and see if some leak more than others.

Hope this helps.

[Matt Harwood]

PS: The myth that you can't switch to synthetic and go back to regular oil later is just that--a myth. You can mix the two in the same crankcase without worry, and switch back and forth without any issues. Oil is still oil, they're compatible with each other, it's just that one is slipperier and more stable than the other. This is why I am puzzled over "synthetic blends." What's the point except to extract more money from your pocket? It's expensive like a synthetic, but has regular oil in it so you lose the benefits of the synthetic. A total waste of money either way. Pick one or the other, but don't waste money on the synthetic blends which really only offer the disadvantages of both, not the advantages.

[Durant Mike]

Matt I have to agree with you. I happen to like Red Line synthetic oil. Used in in my motorcycles and then in my TR6 and never had any issues and my engines seemed to run well on it. I was curious and wrote the technical people at Red Line to get their thoughts on using synthetic in the older cars pre 1930 or oil filters. The chemist with the company wrote back that he was running it in his Model A and never had any problems with it. The bases of the letter stated that most antique auto people change their oil at least once a year if not more. The cars are not driven as much so any impurities that accumulate in the oil won't be there long. I'm going to run it in my Durant when she's done.

[Guest morerevsm3]

PS: The myth that you can't switch to synthetic and go back to regular oil later is just that--a myth. You can mix the two in the same crankcase without worry, and switch back and forth without any issues. Oil is still oil, they're compatible with each other, it's just that one is slipperier and more stable than the other. This is why I am puzzled over "synthetic blends." What's the point except to extract more money from your pocket? It's expensive like a synthetic, but has regular oil in it so you lose the benefits of the synthetic. A total waste of money either way. Pick one or the other, but don't waste money on the synthetic blends which really only offer the disadvantages of both, not the advantages.

"hydrocracked synthetic oil" or "semi synthetic" is, in most cases, marketing BS, and is mineral oil slightly more refined and maybe an extra additive, I wouldn't run anything but a group 4 or group 5 full synthetic oil, if you are worried about Zddp, you can buy it and add to synthetic oil

[Guest shadetree77]

The thing about leaks and synthetics isn't that they're causing old seals and gaskets to fail, it's that the synthetic oil molecule is different than the regular oil molecule...... But those same molecules will find their way through holes through which regular oil molecules can't fit. So while some guys use their anecdotal experience with some synthetic oils as proof that it causes leaks, the real reason is that the holes are still there, it's just that one oil can fit through them and another one can't.

I agree with these statements wholeheartedly. My opinion is that if you have an old engine that has not been rebuilt recently or even rebuilt at all I would not use synthetic oils in it. Here's a short story to back up that opinion. I have a 1998 Jeep Wrangler. When I bought it, it had around 90,000 miles on it and it was running strong with absolutely no leaks. After owning it for awhile, I decided to start using synthetic oils in it because I had heard they performed better which is probably true. However, a short time later I developed an oil leak. As the miles added up and time went by the leak slowly became worse until finally I was at the point that I had to add oil at every gas fill up. Eventually, I began to hear a clunking noise in the lower end of the engine. Long story short, it was a spun bearing that resulted from continually running with an insufficient oil level due to the constant leak. Now the Jeep is sitting in my yard immobile and collecting dust. The synthetic oil found the pre-existing holes in my seals and seemed to make them worse with time. But I'm not totally against synthetics. I just think they should only be used in a newly rebuilt engine and NEVER in an old engine. On a side note, when I took the engine apart looking for the cause of the noise everything was squeaky clean. Not a bit of crud or sludge anywhere. That synthetic oil really keeps the engine clean.

Edited August 17, 2012 by shadetree77 (see edit history)

[NTX5467]

The problem is finding WHICH oils are using the higher-group level base stocks for their motor oil! There has been some speculation over in www.bobistheoilguy.com forums, but nothing "concrete".

When the whole zddp situation surfaced, CompCams recommended either "synthetic motor oil or Shell Rotella T" motor oil. Further research revealed that "SL" rated synthetic motor oil has approx 1000ppm of zddp in it, without regard to the brand. The full-diesel Rotella synthetic 5W-40 usually tests out at about 1400ppm, though, even with a "gasoline" AP service rating of SM (but NO ILSAC rating!!!!). So, going back to that original recommendation from CompCams, any synthetic might be fine, but when it was made, SL synthetic was common. Be that as it may. CompCams, Edelbrock, and some oil additive manufacturers now sell their own zddp additives.

Even among normal "dino" oil, some brands will wick through cork/rubber gaskets much sooner than others will, by observation and experience. Even oils of the same viscosity ratings!

Just some thoughts,

NTX5467

[Guest morerevsm3]

I run redline oil which is group 5 base stock, and add zddp