View Full Version : Synthetic Oil Comment---Bad News??

12-14-02, 11:05 AM
I was reading my Covette Fever Mag last night when I read something a little disturbing. February 2003, page 33 ,photo #4. let me quote"It seems that cleanliness was an issue when they were assembled, and the combination of time, heat cycles, and SYNTHETIC OIL will all but gaurantee a leak" .
What's up with that? Do synthetic oils leak more than regular oils?
I just bought an 86 and changed the oil to Mobil 1. Was that a bad move? Your comments please...--John.

12-14-02, 11:35 AM
I switched the ZR-1 and the 84 CF to synthetic oil two years ago with no problems. I believe the theory is that the synthetics have a better detergent quality and remove carbon build up from seals and gaskets, which may cause a leak. Should that take place the only solution I think is to replace the seal or gasket. I believe if you have a few miles on the clock they recommend using a non kerosine based engine flush first before switching to synthetic. Just my experience. 84 CF 91 ZR-1

12-14-02, 01:37 PM
Synthetics tend to leak more because they are thinner.

They are also a 'narrower' range of product, so they tend not to sludge when the lighter aromatics burn off. I am not sure the detergent level is any higher than any quality oil, but the insides of the engine seem to stay cleaner. Perhaps the lower viscosity keeps the gunkies flowing to the filter better.


12-14-02, 01:56 PM
It's not recommended to switch to synth. on a non rebuilt engine or one that has accumulated a reasonable amount of miles.

The leaks are caused by cheapo cork gaskets.Some quality gaskets will keep the engine leak free.

As for the synthetic, there are a couple of sorts. The cheapest is the reconstructed mineral oil with additives.

The pure synthetics come in the di-ester based oils and poly-ester.

The di-esters are the cheapest but since the oil is constructed of 1 sort of chain the complete structure of the oil will disintegrate when you hit the break down temperature.

The more expensive poly based oils are the ones to use in your engine (if you want to fork over the bucks, that stuff is not cheap)

The poly based oil has a selected range of chains (bonds) and when you hit the critical temperature only the weakest bonds (longest chains) will break down, leaving the majority of the oil intact.

This is only a simple representation, it's actually a bit more complicated (bring additives into the picture) but that should give an idea of how things work.


12-14-02, 04:48 PM
Well I thought I would be treating the Vette with top shelf stuff using Mobile 1. Your right it is not cheap. The car only has 51k original miles on it. So hopefully, I will not start seeing puddles of oil under it. Maybe there's not that much dirt inside yet.

The Car Whisperer
12-15-02, 01:30 PM
When I tried synthetic in my 86' it leaked oil. There were no oil leaks before the synthetic. I used it for 2 more oil change cycles and it still leaked, mostly around the front crank seal. I changed back to regular oil and the leaks stopped after a few oil changes. I'm sticking with the old fashioned stuff. I change oil and filter every 3000 mi so I don't see any significant gain in using oil that costs 3x the price of good quality regulay oil.

12-15-02, 02:02 PM
I have heard this is a problem with synthetic oil. Any minor leak will leak even more with synthetic. I have heard not to change to synthetic with older cars. How old...I don't know?? I have not changed and will not change on my 64. I have a 98 M3 BMW and have considered changing on that, but presently still run Castrol GTX oil.

12-15-02, 03:00 PM
If your talking about the C4, I don't think it's always the oil. The intake manifold is known to leak after some number of miles, particularly if the assembly plant didn't get all of the oil film off the surfaces, prior to putting on the sealer. I had the problem and resealed the intake and no problem afterwards. Several of my C4 buds have had the same problem of thier vettes "Marking it's terretory".

The Car Whisperer
12-15-02, 06:24 PM
All I can say from my experience is - Had no leaks before synthetic / had leaks after synthetic.

12-16-02, 08:25 AM
I am running penzoil 5w 30 in my stock 89 with a ac delco oil filter
did have slick 50 in there also but to many bad comments about it so i just run the oil and change the filter 25 k miles. no synthetic here......owners manual doesnt say to run it............lou

12-16-02, 08:32 AM
Synthetics are far superior to mineral oils, the properties can be taylored to exact specs, where the minderals are ballpark. I will never run mineral in any of my engines, synthetic means no sludge, clean engine. If you pull an engine that has run on synth apart you will instantly notice the difference.


12-16-02, 09:09 AM
Marck isn't Mobile 1 still a petroleum base? A true synthetic would be Red Line. Chuck

12-16-02, 09:37 AM
It depends on what product line. I'm not sure, but it could very well be possible that the mobil1 is a reconstricted mineral oil.

I have shell Ultra Helix 10W60 (used in Ferrari challenge) and it's a true synthetic.


12-16-02, 10:31 AM
Originally posted by LOUVETTE
I am running penzoil 5w 30 in my stock 89 with a ac delco oil filter
did have slick 50 in there also but to many bad comments about it so i just run the oil and change the filter 25 k miles. no synthetic here......owners manual doesnt say to run it............lou

i'm pretty sure you meant 2,500 miles right?:)
as far as synthetic goes, like mentioned above, it you never udes it and your car has some miles on it, chances are engine will leak, synthetic keeps the engine cleaner and leaves less gunk.


12-16-02, 11:34 AM
Well I kind of knew this topic would create a good discussion, as far as the technical side of oil--it's all greek to me. It seems to be a matter of personel choice. I'll keep the Mobil 1 in there, and if I see any problems this spring or summer, maybe I'll change it back.
Was going to get her out again today, but it's nasty here. Snow and rain coming.....................John.

12-16-02, 12:08 PM
Originally posted by WhalePirot
Synthetics tend to leak more because they are thinner.


This is something that has allawys bothered me??
Isn't a 10W30 a 10W30 regaurdless of it being natural vs Synthetic?

I thought the basic advantage to Synthetics is that they stay fluid to much lower temps and don't break down at higher temps.

I don't see how the same weight oil is any "slipperyer" either??

Just figured the flow rate at a given temp would be what it is regaurdless.

12-16-02, 12:15 PM
The weights refer to the viscosity of the oil. The viscosity is dependant on the chain size of the components and on stuff like viscosity index improvers, they put that in oil to make sure it doesn't thin out too much.

low weight oils have a lot of vii, see it like this. 10W30 is a 0 weight oil that won't thin out more at high temps than a 30 w oil would (or the 10w oil will be as thin at high temp as the 30w would be)

The advantage to synthetics is they are less rpone to breaking down, this means they will keep adequate lubrication with a much thinner oil film than the minerals.

Mineral oils tend to have a lot of VII (especially the low weight, 5W30, 10W30) and VII don't lubricate, oil does.

The VII are coiled up polymers, coiled up they hardly influence the viscosity, when it gets hotter they coil out, long strads do influence viscosity.


12-17-02, 03:38 PM
Twinnie gives a very good technical view... i will put in in lamens terms to possibly help a bit

Synthetic oil is man made, so they can make every particle of oil the same size, we will call this size X for our sake.

X is just the right size particle of oil, it is small, but not tiny, and not large... this allows for excellent consistancy and protection

Standard oils have a wide range of particle sizes, so, while there are some particles the same X in size, there are many more particles bigger than X, and a minor number smaller than X. Any particle Bigger than X won't protect as well, smaller won't either... there is also a problem with the lack of consistancy.

In synthetic: Since all the oil particles are X in size, if there is a path in any seal or gasket in the engine that an X size particle can get out, any particle of synthetic can work its way through, so you have a nice steady leak.

In standard oil: you may have a few smaller, but the few bigger particles may even act to 'plug the leak' or path out of the engine... so fewer leaks.

The L98 has common leaks with standard oil... with the LT1, those leaks were attemted to be fixed, but the addition of synthetic oil created new leaks...... When my corvette tech talks about the leaks, he refers to the engine as 'seaping oil' since it is just slowly seaping out of the engine.... I have had 3 C4's, my L98 leaked (standard oil), my LT1 did not (synthetic), and my LT4 currently leaks (synthetic).... I think at the end it comes to luck fo the draw... hope this helps:)

12-17-02, 06:27 PM
Clear as oil :crazy

12-17-02, 07:33 PM
LOL, Man! I thought a leak was just a "Leak". Never knew it was rocket science, but thanks for the info.

12-17-02, 08:38 PM
I ran Mobil 1 all last summer. Not a drop leaked. As a matter of fact, I think a few weeps I had the year before actually leak less now. I am very satisfied with the Mobil 1.

Radar :beer :)

12-17-02, 09:15 PM
Originally posted by Corvette-Pilot
Clear as oil :crazy

sounds like my attempt failed:( but, it was worth the try, right?:eyerole

12-17-02, 09:15 PM
I understand what you mean ;)

12-18-02, 07:33 AM
Originally posted by Vettelt193
sounds like my attempt failed:( :eyerole

No not at all,
I greatly appreciate the explaination as I'm sure many others do.
It really makes sense, just makes my head spin.

I would also like to add that I changed over to Mobil 1 in my 97 RAM 4x4 truck at 35-40k miles.
I now have 55k and have not seen anything dripping that wasn't before.
So at least in my case it has not caused any trouble.
Matter of fact, it has been in the low teens each morning the past few days so I'm sure this has helped in the easier starts.
Just wish I could get started at these temps :s

12-18-02, 08:44 AM
I love to read the threads on oils and filters. This one was another good one and informative. I only wanted to comment on the use of Synthetics and new engines. I recently purchased a BMW X5 4.4i. My first oil and filter change will be done when the electronic monitor dictates. It usually is required around 14-15K miles. I now have about 10K miles on it. As I am told, BMW uses pure synthetic oil in their motors.

Also, I have been very fortunate with all the motors I have built or bought. No long term leaks, until this last one, which I built and has a slight rear seal leak I don't intend to fix it until I rebuild it. This is the first motor I have broken in with standard oil and run synthetic oil specifically.

12-18-02, 04:39 PM
I was very reluctant to use Synthetic til I tried it.
In a Motor Home with 68k now 77k no leaks, less oil use, lower temp. In 2 Jeeps with 6cyl at 89k and 92k no leaks, less usage, not sure about temp. Both have 102k and 113k. In my '86 Corvette changed at 98k now 110k same result.
The stuff is great. Mobile 1 with Pure-one filter, soon to be K&N on all.

12-18-02, 04:42 PM
Originally posted by Barrier
Mobile 1 with Pure-one filter, soon to be K&N on all.

is pure one really that good? i use Fram on both my cars and they seem to be working fine

12-18-02, 05:15 PM
The FRAM is about the worst filter out there. The cheezy paper contruction makes that unfiltered oil can leak past the valve in the filter (the end caps are paper and the rubber anti drainback valve seals against these).



I use a tall style System one oil filter, no need to buy new filters and I don't have to take the filter case apart to see if there's metal shavings in the filter.


It has a fine steel gauze filter that can easily be cleaned.


I had long style WIX before this one and was very satisfied.


12-18-02, 05:48 PM
no more Fram for me then .......i just thought that since it was made in Israel it's a decent quality oil filter........thanx for posting this


12-18-02, 05:54 PM
Wow, that was some oil filter study. Check out the ad for Mobile 1 using an 86 Vette. I was cruising Ebay today and came across it.

12-18-02, 07:34 PM
The synthetics do hold up better under high heat conditions. There are several articles on the subject not just for vette but other applications as well. I'll choose Mob 1 or the other synthetics, any day, over conventional lubes, particularly here in fla.
Merry Christmas Guys!

Dave L.
12-18-02, 08:52 PM
Hey guys,as an observer on this post I was wondering how often you change your oil when using synthetic. I started using it in Lori's car (98 Cavalier) about 6 months ago and I have been changing it out between 5-6K. She puts so many miles on that car, using regular oil I would be changing oil in her car about every 6 weeks!

Thanks........ Dave

12-18-02, 09:34 PM
6000 on mine between changes

12-19-02, 07:11 AM
Originally posted by BURGLAR
Hey guys,as an observer on this post I was wondering how often you change your oil when using synthetic. I started using it in Lori's car (98 Cavalier) about 6 months ago and I have been changing it out between 5-6K. She puts so many miles on that car, using regular oil I would be changing oil in her car about every 6 weeks!

Thanks........ Dave

Sounds like she does a lot of highway driving ?
I would think this would allow you longer times between changes vs city driving.
The engine isn't under the same stresses.


Dave L.
12-19-02, 07:15 AM
Thanks Guys. She does a LOT of highway driving. I should be good with 6000 mi intervals.


12-19-02, 07:48 AM
I think it's fairly well established that you can go 6k miles or more between OIL changes, but still make sure to change the FILTER every 3k miles. I change oil in my daily driver (96 Legacy Outback) every 10k miles, but filter every 3k or so. 130000 miles and no problems other than the leaks those cars are known for anyway (see, Vettes aren't the only ones with legendary oil leaks!).

12-19-02, 07:55 AM
yea, my owner manual says 7500 mi for non-dusty highway miles....and that's on Dino Oil. (2000 Silverado).
I'd think the Synthetic could easily go for 7500 in the same conditions...but it's all a matter of what/who we REALLY believe.
I still run the Dino Oil, change it myself every 3K for under $10,
so it's not too much overkill/waste $ wise.

:Steer :w

12-20-02, 10:37 AM
Having never changed just the filter on any car, I have a question. How much oil is going to leak out when the filter is removed? Probably just a little, but I would like to make sure.

12-20-02, 03:27 PM
I haven't yet changed just the filter on the Vette (only put 2500 miles on it) but on the Outback I get very little - between the filter and what drains out I have to add less than a quart.

12-20-02, 03:48 PM
You can't go wrong with the synthetic oil. I've been using Amsoil for 10 years. (the first synthetic oil made) I have never had a problem with it, nor have I known of anyone else to have a problem with it, leaking or otherwise. In fact, in '94 I put it in my brand new Harley right after my 500 mile check-up, and the dealership did it for me. They were reluctant of course because they want their product in it, but the Amsoil guys explained and answered their questions and doubts. Amsoil even warrants your parts if anything does happen due to the oil. It is 100% synthetic. I use it in all my cars, trucks, and even small engine equipment. The Jack Nicklaus Country Club I had worked at uses the same oil in their entire gas powered fleet, including the company trucks, club cars, (which get rebuilt all the time), their small engines, etc. They buy the stuff by the 55 gallon drum.
Not using the synthetic oil on high milage and rebuilt engines is a myth, the oil definetly helps keep it clean. As we all know that every time we turn the key in the car, deposits and grindings come off the parts. The synthetic oil coats those parts for up to a year, even with the car sitting that long. Other advantages are longer oil change intervals, vehicles able to run up to 20 degrees cooler, parts protected, doesn't break down. I been so impressed, I became a dealer. I don't push getting the accounts like I should, I only continue my dealership to get the discounted prices. Hope some of this info. helps with the doubts and concerns, and I apologize for the length.

Bob Yates
12-23-02, 08:36 AM
Well I'm going to throw a wrench in the middle. I use a blend. Semi- synthetic and I change about every 7,500 miles. I use it in all my cars and I think it just makes me feel better in side. Don't know what it's doing inside my engines but everything seems to be fine. If it ain't broke don't fix it. Does anyone know what the TBN ( total base number) is for synthetic oils ? I sure don't. But I know that's important.

12-31-02, 10:12 AM
Bob, your question about the TBN, total base number for synthetic oils can be be found @ go-synthetic.com/properties.
For Amsoil, (for example): Their series 2000 0W-30, which I use a lot, is >11.0
20W-50 is >11.0 ----- the XL 7500 series for 5W-20 is >9.0, 5W-30 and the 10W-30 in the XL 7500 series is both 9.0
the XL series was produced primariarly for service stations to provide to customer to get service on a regular oil change. Which is 7,500 miles. The regular Amsoil 100% synthetic changes for oil is 25,000 miles or 1 year. Their filter changes are every 6 months. The series 2000 0W-30 oil change is 35,000 miles.
The 100% synthetic 5W-30 TBN is >11.0, 10W-30 is also >11.0
They have a semi-blend also, 10W-40 -- >11.0
The high performance sythetics for 10W-40 and 20W-50 are >12.0

Bob there are even more and I do believe for the oils you may be using too. If the Amsoil stuff is interesting to you let me know I could get you some more info.

Bob Yates
01-07-03, 12:06 PM
Thanks for the info. I just got rid of my 81 last August. I mis it. I now have a 86 C4 conv. with aluminum heads. It's cool but my 81 was show stopper. I owned it 7 years had a lot of fun with it . I have a lot of new parts which I never used . Weatherstrips and stuff if you would like a list let me know. I have a vacuum powered heat rizer that's brand new , new GM motor mount. All of the foam seals that go around the raditorand more. Take care......Bob

01-08-03, 09:22 AM
Bob, thanks for the reply. If you don't mind I would like to get a list from you regarding your '81 parts. At the moment I don't need anything, ( as far as I know ), we've got the snow here, and I got the car in November, so it's just been the light tinkering, tightening thing. But I do need a rear view mirror, the glass reflecting stuff is starting to go.
E-mail @ bwalton41@hotmail.com

Thanks --- Brian

"94 Sixspeed
01-09-03, 02:06 PM
Originally posted by rrubel
I think it's fairly well established that you can go 6k miles or more between OIL changes, but still make sure to change the FILTER every 3k miles. I change oil in my daily driver (96 Legacy Outback) every 10k miles, but filter every 3k or so. 130000 miles and no problems other than the leaks those cars are known for anyway (see, Vettes aren't the only ones with legendary oil leaks!).

You got to be kidding... This will probably extend the life of your car by at least 5 or 10k miles.. It will last at least 250k either way, or at least it should.. By then it's time to think about some real power... Or a whole new ride..

01-13-03, 08:01 AM
Hey, if you really like the car you can keep it for as long as you want, especially using Amsoil. The Amsoil Action News mag. they put out has testimonials in it all the time about tear downs and the engines still remaining at specs, even with the big rigs. Log onto to amsoil.com for more info. or if you need other info. like a catalog of spec sheets please let me know. I would also be glad to order whatever you need or help you become a dealer yourself. '94, remember it will also help lower your temps. 10-20 degrees in the engine and tranny. The oil does not break down and will not void any factory warranties, they put it in writing.



01-13-03, 08:46 AM
All I can say is I had a minor valve cover leak before I switched to Mobil 1, I still have a minor valve cover leak after switching to Mobil 1.

I switched at 120+K a year ago. It uses less than 1 qt between changes. I'll keep using Mobil 1 because the engine seems happier.

01-13-03, 09:54 PM
jaa1988, have you determined where the leak is?, a bolt (coming out of threads), type of gasket, or gasket not lined up properly?
Do you think it is the oil causing your leak????:(
You will find the 100% synthetic oil is a little more "stickier" , I can't say that it will help for sure, but your engine would still be, if not more happier.
I think there has to be some type of source where your oil is being allowed to escape. Any pitting on the heads? Good Luck