Synthetic fluids - what I know to be true

[jmil1974]

Here's what I do know for sure from my experience and others more experienced than I:

The Chevy mechanic that lives next door only puts synthetic fluids in when possible. He told me it runs significantly cooler in differentials, especially when towing. No reason it wouldn't be the same story with trannies or engines.

I also know that if you run synthetic in an engine with older gaskets and seals, it WILL leak. It's better, but it's messier and likes to find a way out due to it's smaller molecular size and "slipperiness."

I recently mixed conventional and synthetic in my diff. I bought Quaker state regular dexron to do my tranny fluid and QS 10w40 4x4 for my motor. I would use synthetic but I don't feel like changing all the seals at this point. If there are no leaks in my tranny or "new" motor, I may go synthetic on the next change.

Opinions, especially on brand experience encouraged.
Thanks!
Jason

[Project1970]

We've used Mobil1 in pretty much everything except my truck for years (it gets Mobil 20W50 to cut down on the oil consumption...between that and the new heads / etc, it's down to about 1/4 to 1/3 of a quart lost after the better part of 1000mi!). The '94 Z28 has about 81,000 miles and has gotten Mobil1 15w50 since the second oil change (the first one was to Mobil1 10w30 when we discovered the rather common LT1 oil pressure problem...when switching to synth, LT1s don't build enough pressure with 10w30) and still runs great, zero oil burned, just a minor drip at the moment which appears to be around the oil filter seal, probably just a bit of dirt. The '97 Benz has seen Mobil1 since we got a hold of it (my grandma took it to the local Benz shop, which probably used synth as well) and it just turned over 60,000 miles IIRC...no problems / leaks / burning at all there either. Our '97 Suburban had it after the first change and got it until we traded it in after 97,000 miles...and while it had more than its share of problems, not one was oil-related. Same deal, no burning, no leaks, nothing.

My truck will get it after we rebuild the bottom end, and the TrailBlazer will get it with the next change (it just turned 2600mi).

Oh, FWIW - all of the above synthetic changes have been done at 5000 mile intervals. The oil coming out of all of 'em sure looks a lot better than the oil out of my truck after, oh, 30 miles. (quite black)

[COBALT]

I've always heard the opposite about synthetics and differentials. I've heard they run hotter. Right now I'm using a 90w blend of synthetic in my old HO52/72 (or whatever). Randy's Ring & Pinion put it in when they worked on my carrier.

[Church]

I'm running Amsoil's synthetics in my motor, trans, transfer case and both diffs in my 2000 WJ Jeep. When I switched to syn's I saw an improvement of 1.8 mpg! Not only that but my rear diff is sustantially cleaner now that I have switched it over. When I change the motor oil, it still has the golden look to it. It looks as if has not even been used! I do agree with you about the seal problem. I sell Amsoil sythetics and have to warn people about this. This is not only because of the "smaller molecular size and slipperiness", but also syn's keep your motor cleaner. They wash all the grime off of the back side of the seals. This will also create leaks since the dino cant wash nor recondition the seals. There is always someone out there who will disagree with you about the syn vs. dino oil issue. If you want to try it in your motor, it could not hurt, if it does leak just swith back to dino. Hope this helps

[Huck]

Mobil 1 is what Porsche & Mercedes install in their engines and what they recommend. I have used it my farm tractor for winters where it's too cold for any oils and it stays thin. I also converted by 97'vette 6 speed trans to it. Had a history of hanging up between gears without trying a quick shift. Mobil 1 Dextron syntehtic solved that problem. My transmission shop owner uses synthetic in his transmissions. The best mechanic I know who is employed by a local millionaire to maintain and restore his Ferrari's etc. uses Mobil 1 in an old Porsche 928 that he raced for years at Mid-Ohio. After over 200K miles, he pulled the motor to do a rebuild and couldn't find enough wear to justify the work so he just reassembled it. Haven't noticed any leak problem but would not be surprized. If you have a keeper and you want it to last forever, the investment is probably worth it. Huck

[jmil1974]

Thanks for the opinions, fellas. I'm starting out with dino on this deal just to see what kind of condition the seals in my "new" motor are in and to see if any leaks pop up. If it ends up being pretty tight, I'll definitely switch to Amsoil or Mobil 1 next time around.

Thanks again,
Jason

[crazy longhorn]

I am running 85/140 richmond synthetic in the rear diff, as reccomended by richmond for their gears. I was told run a GL6 or higher rating,basically richmond or redline synthetic by the reccomendation. Also , no GM addative for the posi unit & havent had any problems with the diff. i still run the dino stuff in the engine, but it hardly ever sees more than 1000-1200 mi between oil & filter changes(once a season). crazy AL

[Project1970]

Regarding positraction rear axles...I've heard that with Red Line gear lube, you don't need the posi additive, it already has it. However, I can say from experience that Mobil 1 gear lube still needs the additive...

Oh, and I forgot to mention, my 700R4 is running Red Line tranny fluid. 1600mi so far and no problems whatsoever.

[PICKMUP]

Just a note: Remember, don't break a new engine in with synthetic. It is too slick and the rings will not seat. You will get a permanent glazing on the cyl walls and going back to dino after that will not fix it. Run a good 3K before going to syn.

[jmil1974]

Thanks Pickmup. I heard that and was going to go that way anyhow. I said "new" engine because it supposedly has only 3-4k miles on it and I picked it up for a nice price froma guy who just used it to pull in and out of the garage whilst building his Pont 455. It certainly is clean enough to be that low mileage. We'll see how she runs when I get her in.

Thanks again,
Jason

[yellowgmc]

what do the factories use to greak in their engines? vipers' corvettes and porches ( the car i can't spell) all come new with mobil 1 in the pan. i've heard theres no problem using it on a new engine as long as you follow normal changing times. btw i use qs 4x4 10w30 in my new truck and my old truck. never had any problems. my dakaota had 270k kilometers on it and to my knowledge the engine had never been opened up. brought it with me when i moved from canada. that was a pain.

[PICKMUP]

OK, hate to beat this old dead horse, but it might be important to someone who screws up their new engine. Look at Car Craft, Sep, 02, p.94 for a discussion on breakin oils, ring manufacturers' guidance, & why Corvettes are different. We don't have Corvettes...we don't use synthetic oils for our break ins.

[yellowgmc]

what's the gist of the article? i don't have that issue. i had read something in another mag about it being okay a couple of months back. don't remember which on though, too many subsrciptions and they wife just cleaned out my collection (read garbage). thanks.

[jmil1974]

I read that article. If I remember correctly, you can use synthetic oil for break in on motors with tolerances so tight that they don't really need breaking in anyway. That sound right?

[Michael A. K. G]

Originally posted by COBALT
I've always heard the opposite about synthetics and differentials. I've heard they run hotter. Right now I'm using a 90w blend of synthetic in my old HO52/72 (or whatever). Randy's Ring & Pinion put it in when they worked on my carrier.

Here's what I think the discrepancy is.

Synthetic gear lube doesn't transport heat as efficiently as conventional. Therefore, it should not be used to break in a new gearset; the excess heat generated during break-in will remain at the gears, and they will overheat.

But once breakin has completed, the lube is considerably more slippery, and there will be less heat generated in the first place.

[Ackattack]

I plan on using mobil 1 in my engine when I get a few more miles on it (500 on rebuild) and solve my minor oil leak (I think the intake is leaking a little), so I'll probably switch to Mobil 1 about 3500 miles.

I've used Mobil 1 in my car from day one, that's what GM recommends and starting in 2002 they came with it from the factory.

[1-PU70]

Just one more thing. Regular oil has ash in it and that is what builds up in your engine after time and gives the moter and used oil that dirty look. Syn oil does not have ash in it and that is why it stays clean and keeps your engine clean inside.