I always use Castrol semi-syth in my jeep and change it about every 4-4.5k, and i'm not hard on it at all btw

but ive always wondered if semi-sythetic oils have any advantages?

I've heard that they are a good tradeoff b/w dino and synth oils, but i've also heard that semi-syths are just to fill a market gap of "semi-convinced" people

school me tdub

4/24/2008 11:24:59 AM

I donno if this is true, but a myth I've heard about synth oils of how you shouldn't use them in older cars or high mileage cars that used are used to running on reg oils because the particulates and consistency's in synth oils are much smaller than conventional oils, therefore oil is more easily to leak through small fissures in o-rings.

Anyone? Myth or is there some truth to it?

4/24/2008 11:40:33 AM

That is correct.

4/24/2008 11:45:28 AM

i always heard it was because the detergents in the synthetics would clean away deposits that are actually preventing leaks around seals, etc. in other words, you'd switch to synthetic and develop oil leaks shortly thereafter.

Any truth?

4/24/2008 11:47:41 AM

i, too, have heard these things

from mechanics i trust, too

so i'm going with yes, it's true, and don't put synthetic in your vehicle if it's 1.) high mileage on dino oil or 2.) old (which would probably fall into category 1 anyway)

4/24/2008 12:05:31 PM

^(everyone above) I've heard this as well and while I believe its true, there are exceptions.

I started using full synthetic oil in my car at 175,000 miles and have never had a leak.

4/24/2008 12:34:22 PM

I've heard from a few reliable sources that Pure sythentic oil doesn't exist anymore. They are all semi-synth now. Is there any truth to that?

[Edited on April 24, 2008 at 12:37 PM. Reason : .]

4/24/2008 12:36:59 PM

i started synthetic in my 00 taco 3.4v6 at 91k and shorty thereafter it began using a little bit of oil between changes but i never saw it drip oil or anything

4/24/2008 12:41:09 PM

I know that some oils that are advertised as "full synthetic" actually aren't, but some are. I don't know the technical explanation for it though.

Mobil One is full synthetic though, I know that for sure.

4/24/2008 1:26:11 PM

my cars leak enough on dyno. lol i can only imagine the mess with fully synth

4/24/2008 1:31:53 PM

I switched from dino to full synth in an 8 year old Lincoln and saw no leaks or increased oil usage whatsoever. (It did only have about 50k on it at the time, but still an "older" vehicle)

4/24/2008 2:13:40 PM

Quote :

"I've heard from a few reliable sources that Pure sythentic oil doesn't exist anymore. They are all semi-synth now. Is there any truth to that? "

no

Quote :

"Mobil One is full synthetic though, I know that for sure."

actually.....

mobil 1 comes from a group III base stock, which is derived from petroleum. true it is not a dino oil, and is not a blend, but is made from chemically altering a petroleum product.

group iv base stock oils are really the only "fully synthetic" ones (fully synthetic base stock)... they're rather hard to come by and can be expensive... elf and motul are two group iv base stock oils.. i use to elf lubricants (a division of total lubricants) and usually have some around...


as for "semi-synthetic" oil.. it is usually a dino/synthetic blend...


[Edited on April 24, 2008 at 2:36 PM. Reason : http://www.pecuniary.com/faq/oil-base-stock.html]

4/24/2008 2:30:15 PM

whats ams ?

4/24/2008 2:36:04 PM

what what?

4/24/2008 2:36:44 PM

4/24/2008 2:38:07 PM

amsoil is group iv.. a lot of people think its the best oil in the world, when in reality i dont think its better than any other oil made from group iv base stock.

also, castrol syntec recently changed to group iii sometime in the past few years (probably around the time that mobil 1 did).. but you can get what they call "german castrol" which is supposedly green... its still group iv.. not easy to find in the US, tho.

i also heard that royal purple is group iii..

[Edited on April 24, 2008 at 2:41 PM. Reason : http://www.bobistheoilguy.com]

4/24/2008 2:40:35 PM

^ & ^5

That's what I heard. I couldn't put it into those words, but w/e. I remember hearing about that german castrol stuff, and that's what made me think that most "sythentic oils" weren't actually PURE/TRUE synthetic. Thanks for confirming...

So what is the concensus? For a new engine (already broken in), I would assume that synthetic blend is good enough for a DD and the occasional "spirited driving?"

4/24/2008 3:08:50 PM

what car is it? i would just use whatever oil meets the car manufacturer's specifications

4/24/2008 3:55:25 PM

LT1

Its got Castrol 20w50 for the break in period. Oil was changed at 1,000 mi and analyzed. It's been another 1,000 miles an I've thought about changing it to full synth. That's when I was told that REAL/FULL Synthetic is hard to find. Since I don't track/race my car and it's mostly a DD, I figure full synthetic isn't crutial and a blend will do. With that said, I will probably go Mobile 1 or Castol Syntec, whichever is on sale (Unless someone can tell me why Mobile 1 is superior...)

[Edited on April 24, 2008 at 4:11 PM. Reason : .]

[Edited on April 24, 2008 at 4:17 PM. Reason : .]

4/24/2008 4:11:30 PM

that should be fine..

i have Elf (i think it is NF Solaris) in 5w30 if you're interested.. its like $7/liter...

4/24/2008 4:15:32 PM

there's a lot of truthiness in this thread.

4/24/2008 6:15:19 PM

Quote :

"mobil 1 comes from a group III base stock, which is derived from petroleum. true it is not a dino oil, and is not a blend, but is made from chemically altering a petroleum product."

where has exxonmobil/mobil1 admitted to being group III? I've heard rumors that mobil1 was a mix of PAO's and group III, but nothing substantial has popped up, i.e no one has thrown down the money for a definitive analysis (AFAIK).

Redline is a true group IV. That's why it costs ~$7 quart.

Synthetic oil doesn't CLEAN any better than regular oil. What it does do is keep things from building up. With regular oil, the large oil molecules will fill up the gap thus preventing a leak or slowing one down. Since synthetic oil has uniform molecule size, nothing can stop them.

Some cars b/c of tolerances, will use a little bit of synthetic every couple thousand miles, whereas their regular cheaper oil counterpart will use less, just b/c of the size of the molecules. With synthetic, all the molecules are the same size. With regular oil, you've got larger, middle and small all in the same pot. It'll burn off the smaller molecules first, but the larger ones will remain.

Semisynth can be a mixture of true group IV and group II or group II and III or group III and group IV.

It's all marketing.

AMSoil is ok oil, but it thickens up wayyy past it's specs sometimes and that's really NOT cool. I used their oil for years, but I always got SHITTY gas mileage. There was a test online a few years ago that put their oil in camaro or something and ran it for a year. The results were not good. I had my oil analyzed by blackstone labs everytime I changed a filter and topped up, they were not happy about the 5w30 thickening up to a 10w40 after 10k miles.

There really isn't any point to using semisynth, unless you want to extend your drain interval slightly. As long as you change or oil on a regular schedule based on the amount of driving/conditions, any oil will do well.

You can either use conventional group II or group IV.

It's like midgrade gas, there aren't cars that require it, but it makes drivers feel better about not using premuim b/c they are either too cheap or silly.

[Edited on April 24, 2008 at 7:10 PM. Reason : d]

4/24/2008 6:54:20 PM

ok.. some searching shows that mobil 1 is at least partly group iv

Quote :

"Mobil 1® uses high-performance fluids, including polyalphaolefins (PAOs), along with a proprietary system of additives. "

http://www.mobiloil.com/USA-English/MotorOil/Synthetics/Why_Synthetics.aspx

it looks like it is a blend of group iii and group iv stock, tho.. still definitely a good oil.. i ran it for years.. i really only switched to elf b/c its a lot more readily available for me..

4/25/2008 10:28:29 AM