Synthetic Oil

[Mel Goff]

The previous owner of my '74 big block put in synthetic (Mobil 1) oil. The original builder/restorer advised me to get the Mobil 1 out and use a good quality multi grade oil such as Valvoline or Castrol. He said that this motor never leaked a drop but synthetic oil is so 'slippery' that it causes oil to leak right past the seals/gaskets on some motors. The motor has less than 1,300 miles since redone to factory specs. Any input on this?

Thanks in advance for your replies. Mel Goff

[grr]

Re: Synthetic Oil

Mel, is the car leaking oil now? I break in engines with regular otc base oil and run for an hour then change. Then use nothing but synthetic. All the bnew cars use it. I use it and have been since it came public years ago. Your engine will like it better also. What do the new corvettes use? synthetic or regular oil? It's your call.By the way the engines I referred to all pull 6000+ RPM and no oil seal leaks. Again it's your call.grr#33570

[Robert B.]

Re: Synthetic Oil

I have it in my 61 ,65, and 67 427 for last 8/10YRS. and have never had any problems. This oil has been tested and the results are good enough to put in the new corvettes at the assembly line. If your not experiencing any leaks, It is worth the extra $20.

[Patrick T.]

Re: Synthetic Oil

As soon as I purchased my '67, the first thing I did was put 5 quarts of Mobil 1 synthetic oil and have had no problems. The only I problem I ever experienced was with an M-22 Rockcrusher, which I did a total, meticulous rebuild on, and put Mobil 1 synthetic gear lube in, and it leaked like a seive. I gave up on that and just put regular 90 weight in and that cured the problem.

[Gary S.]

Re: Synthetic Oil

This builder must have an old wife around, because this is one of the old wives tales that seem to be perpetuated by well intentioned folks who don't do their homework. Oil is oil and 10W-30 synthetic is no more "slippery" than current 10W-30 petroleum based oil. I don't even know how you compare slippery qualities among oils. The significant advantage to synthetics versus petroleum based oils is their ability to move at low temperatures and their resistance to breakdown at high temperatures. Corvette Fever (maybe Vette) magazine recently ran an article on oils. The final analysis is to do whatever you like. Most of us don't drive our classic Corvettes enough to warrant the use of synthetics, considering the price. The use of a good, high quality petroleum based oil in your rebuilt engine will insure that it will give you years of reliable service. So will synthetics! I have used them in all of my cars from my 66 to my 77 Buick to my 97 Mustang.

[Juliet P.]

Re: Synthetic Oil

I had some oil pressure problems (very LOW pressure at idle only) after the engine was fully warmed up when I switched to synthetic oil. I have a '70 350/300 Auto. I double checked with a second mechanical gauge to confirm it wasn't the gauge, but indeed the oil pressure. Admittedly a large part of the difference in oil pressure is probably due to the weight. Last oil change I inadvertently grabbed the 15W50 Mobil 1 synthetic instead of my usual 10W30 Castrol. I guess I was having a blonde day.

The behavior at RPMs above 1000 or so is about the same with the 2 oils, with perhaps the synthetic 5 psi less than the conventional oil. I get about 40PSI at 2700RPM conventional and 33PSI at 2700RPM synthetic. Cold idle at 1000RPM is about 30PSI for both oils. I haven't had a chance to switch it back to the non-synthetic formulation yet. I thought I'd just leave the synthetic oil in for now and see if any oil leaks I've read / heard about would develop. So far it's been about 2 months and maybe 4-500 miles or so with no new drips on the garage floor that I've noticed anyways.

BTW my understanding of the synthetic oil leak issue has to do with the porosity of some types of gaskets and the molecular structure of the oil. Apparently the synthetic oil is a smaller molecule than the conventional one and the conventional oil swells the gaskets more than synthetic ones helping them to seal better. This to me would imply that it might take a while for the change to show up if gasket replacement has not be coincident with oil change. And a simple retorquing of gaskets might solve whatever leaks might arise. I'm not a molecular scientist so this is based on an engineering interpretation of what I've read and piecing together in my mind how these things might make some sense to me anyways.... ~Juliet

[Bill D.]

Synthetic Oil = lower pressure

Your experience is on the money! The synthetic flows better due to it's makeup. Articles I have read, and my own experience, say 5 psi decrease is correct. I would suggest staying with the 15w50. WB

[Dale Pearman]

Re: Synthetic Oil

Most of us McCof's (Major Cool Corvette Old Farts) like the stuff that was around in the early 60's for Corvettes that were built in the early 60's. I've used Castrol all my life and have NEVER opened up a small block that was dirty on the inside. It's cheap. It works. It ain't broke so why fix it? My 1976 pick up, (Ole Red), has had the same block rebuilt twice without boring, just ridge cleaning and resurfacing. I never change the oil just filters. Most of the oil gets blown out the oil filler tube since my PCV valve is usually pluged up. I just keep adding Castrol on a regular basis. Last time I had damn near 200,000 miles on one rebuild and it was running strong until the lobes fell off the cam! Came home from Cypress Gardens with a spark plug removed from the engine. Haven't been able to hear ever since. Friends called me John Varooom Deere!

My 2001 new diesel truck is an exception. Cummins, who owns a major share of Valvolene, reccomends a special semi-synthetic Valvolene just for the that particular engine. I'm breaking it in on Shell Rotella but will switch to Valvolene at 5,000 miles.

I'd use Castrol in all except late model Corvettes.

Varooom!


CLICK HERE

[Gary S.]

Re: Synthetic Oil

Dale, I wholeheartedly agree with the "if it ain't broke....." comments. I will state that Castrol, Havoline, Mobil, etc, are all great oils. They are NOT the same oil that they were 10, 20, or 30 years ago. That is why the oil containers list API SJ ratings instead of when they used to be SC, SD, etc. The gist of any scientific study on oils is that all of them perform incredibly well. The best thing that we can do for longevity in our engines is frequent oil and filter changes. I sure wouldn't use NOS oil from some long lost 34 year old cache for my 34 year old Sting Ray!

In addition, one of the comments others have made is that perhaps the molecular stucture is smaller, therefore they must seep. I can tell you that since these oils are man made the moelcules tend to be of uniform length, longer than that of petroleum products. Todays gaskets are designed so that no matter what oil you use and what viscosity you SHOULDN'T get leaks. Some folks will have leaks just like some newly rebuilt engines will fail or some new starter or alternator from the auto shop won't work as advertised.

Use what you like and keep on waving. Gary

[Jerry Clark]

Re: Synthetic Oil

Hi Mel:

I am in agreement with those who feel it is an unnecessary expense. Most of the Corvette crowd "treat" our cars to regular service, ( i.e. far more often than most car owners ) I change the oil in my BB about every 500 miles, excessive, probably. If I am leaving the area for an event, it gets cleaned and serviced, I just cant rationalize the added expense only to dump it this often. Maybe I am the minority, but I just love the feel of warm oil in my armpits.

jer

[Ol'Geezer]

Geezer's Cars

[Duke W.]

Re: Synthetic Oil

"Ashless" oils were specified by Chevrolet for racing engines to prevent the buildup of deposits, which can possibly lead to pre-ignition and detonation, but ashless oil have little or no detergent, dispersant, anti-wear, or anti-corrosion additives becaus it's the combustion byproducts of the additive package that leave hard deposits. You don't need these additives in a racing engine because it's assumed that it is being rebuilt frequently, and 100,000 plus miles of service life are not expected. For our cars, we need and want a heavy dose of these additives, which is why I use a CF-4 Heavy Duty diesel engine oil (Chevron Delo). They've got a higher dose of these critcal additives than spark ignition (SJ) oils. The additive package is really more important than the base oil.

The primary advantage of synthetic is a better viscosity index, so it flows better than mineral oil base motor oils at very cold temperatures. Also, it is more resistant to oxidation at high temperatures. Sythetics likely have no disadvantages other that costing more with questionable added benefits. Unless you're driving your vintage Corvette everyday in hot weather and stop and go driving and want to go 5000 to 10,000 miles between changes, it's probably a waste of money. If you drive your car a few hundred to a few thousand miles per year, an annual oil change with a current API specification mineral based motor oil product is sufficient.

Duke

[George Daina]

Been using synthetic for 25 years....

Had a Mobil engineer come to one of our club meetings sometime in '75 or '76. He brought a film to show us what effects Mobil 1 and fossi oils had on two motors that were run 100,000 miles. The fossil oil motor showed cam, bearing, cyl. wall wear while Mobil 1 till had the cyl. wall cross hatches, hardly any bearing wear, after 100,000 miles. I was converted right then and there.

Took delivery of my 91 Blazer S-10 Jan 3rd, 1991, pushing close to 195,000 miles, no oil leaks, no motor noise, no tell tale signs of blue puffs of smoke at startup. After the initial 3,000 mile wear in, first used Mobil, now I use Castrol 5W 50 full synthetic. Haven't used fossil oil in any of my cars since 75/76.

One word why synthetic is far superior over fossil oil. Oil flow during cold start ups, especially in the winter climates. Synthetic flows the same at sub zero temps when compared to oil flow at operating temperatures. 90% of all engine wear occurs at cold temp start ups.

The General says all warranties will be void if fossil oil is used in the Corvettes. Ferdinand Porche says the same, and so does Enzio Ferrari. I guess the General and the two ol' coots know something that we don't.

Anyway, the facts are before ya, m'man, do as ya wish, but I'd find another engine builder.

[Mel Goff]

Re:Thanks everybody for the input...

I really appreciate all of your feedback on this oil question....nice to see that there are so many knowledgeable folks out there.

Thanks again...Mel #33968

[grr]

Re: Been using synthetic for 25 years....

George, Right on.grr#33570