Romeo wrote: It's all nonsense.

Or is it?

From what I understand, "sludge" from dino oil collects around gaskets and seals (and other places). The reported problem with synthetic oil is that is washes these sludge deposits away from around these (and other) areas. Washing sludge away is not necessarily a bad thing, but it IS a bad thing if the sludge itself is helping to prevent oil from leaking from worn seals and shrunken/cracked gaskets.

It is widely reported that many people DO have problems with oil leaks when they switch over to synthetic oil on an older car, especially one with high mileage.

Having said that, I started using synthetic oil on my '86 GT (190,000 KM) when I bought it three years ago and I haven't had any serious leaks.

Romeo wrote: There should still be detergents in any half decent non-synthetic as well. From everything I've learned about oils (And I've done alot of reading up on them), the difference is in molecular stability, nothing more.

Sign up at Pennock's and console all the guys who've reported oil gushing out of their engines with that info.  

I'm operating under the advice of the chemist we had in for a week from AMS Oil. Believe me, if the guy from AMS tells you his oil isn't all too different from semi-synthetics, you take notice. Besides, people also say you couldn't go from full synthetic back to conventional, but given that my trucks both run a conventional/synthetic cocktail, I take that advice with a grain of salt too.

'Sides, I run Gretchin on synthetic. Hell, for a while I was running her on 5W20. No leaks at all.

Romeo wrote: Besides, people also say you couldn't go from full synthetic back to conventional...

...

I've never heard that before.

One of the most common wives' tales out there. Once you're go to synthetic, you have to go completely. You can't mix, and your engine is supposed to 'adapt' to the higher quality oil.

I have no doubt some guys have seen their engines start puking oil once they did a change where they went to synthetic, however I suspect that's more a culmination of high mileage/poor maintenance simply culminating at the moment than anything else. Like I said, detergent-wise (The stuff that actually cleans out the gunk supposedly holding it all together) both conventional and synthetic oils have that in them.

Romeo wrote: One of the most common wives' tales out there. Once you're go to synthetic, you have to go completely. You can't mix, and your engine is supposed to 'adapt' to the higher quality oil.

That's ridiculous, as there's nothing to back up an old wive's tale like that (which I've never heard). Synthetic "blends" (mixed synthetic and dino oil) are marketed and sold.

However, engines leaking oil when switched over to synthetic has been reported time and time again. Certainly not in every case, and probably only in a small percentage of cases, but it does happen.

Robin, don't rely on information bandied about by Tristan or myself. Google it and draw your own conclusions.

Glad to see that my thread has generated a rather lively discussion. Thanks Patrick and Tristan. I think I will hold off on the synthetic oil for now.

But what about those advertised "high-mileage oil"? Are they really any different from the regular engine oil? I'm not sure if they cost the same or not.

Patrick wrote: Romeo wrote: One of the most common wives' tales out there. Once you're go to synthetic, you have to go completely. You can't mix, and your engine is supposed to 'adapt' to the higher quality oil. That's ridiculous, as there's nothing to back up an old wive's tale like that (which I've never heard). Synthetic "blends" (mixed synthetic and dino oil) are marketed and sold. However, engines leaking oil when switched over to synthetic has been reported time and time again. Certainly not in every case, and probably only in a small percentage of cases, but it does happen. Robin, don't rely on information bandied about by Tristan or myself. Google it and draw your own conclusions.

Kinda strikes me of the whole 'Toyota Gas Pedal' thing: I've just learned to ignore people's reports when it borders on mythical levels of explanations sans scientific study to back it up.

As for the high mileage oil, it's about the same cost as normal oil. It's treated to stay thicker under more conditions (So a 10W-30 would try and stay at 30 weight under more temperatures), and is also higher in zinc content (Which is supposed to aid in valvetrain longevity). I haven't heard any complaints about it yet, but I also can't verify if it works.

Boxin' Robin wrote: But what about those advertised "high-mileage oil"? Are they really any different from the regular engine oil? I'm not sure if they cost the same or not.

Robin, you've brought up an excellent point. "High-mileage oil" has additives in it, which among other things, helps to swell shrunken/worn gaskets and seals.

The synthetic oil that I've used in my '86 GT is high-mileage synthetic oil!

So perhaps that's why my relatively high-mileage engine hasn't had much of a problem with oil leaks.  

Romeo wrote: As for the high mileage oil... It's treated to stay thicker under more conditions (So a 10W-30 would try and stay at 30 weight under more temperatures), and is also higher in zinc content...

Gotta link for any of that?

This is from Castrol's website, but effectively the three main differences between High-Mileage and standard oils are:

• A custom blend of polymers to better seal against leaks, especially under colder temperatures (The polymers added to the oils are what determine the weights, as well as their behavior).
• A rubber reconditioner, which inflates or 'baloons' seals, hopefully getting them to re-seal better.
• And 'metal additives' (This would be the zinc compound the AMS employee mentioned, I assume) to better coat and protect wearing items.

No offence bud, but I suspect you're making incorrect assumptions.

I doubt 10W-30 high-mileage oil will "stay thicker under more conditions" than regular 10W-30 oil. It's the same weight, and therefore each oil would have the same flow characteristics at any given temperature.

And zinc is in very few (if any) engine oils anymore. It might still be in some oils formulated for diesel engines and yes, it is in some specialized and marketed oil additives. However, I highly doubt the amount of zinc added to high-mileage oils by Castrol or any other company is any different than what they now add (or not add as the case may be) to their regular oil.

For more info on this, have a look http://www.ttalk.info/Zddp.htm - Here . (The situation may be even worse now than reported there as their latest "update" appears to be in 2006.)

If (and that's a big "if"), if it turns out that "high-mileage" oil has a high level of zinc in it, then all of us with flat tappets should be using it.

It is the same weight, but a polymer that expands with a lower thermal energy will thicken to it's 30 weight faster than one with a high thermal requirement, which will stay at 10 weight longer.

As for the article, I find that dubious, given that AMS (which isn't the most expensive oil on the planet) was the one that told me their high mileage uses ZDDP. As for Castrol, I'm not sure what it is they have, but presumably it would be something that accomplishes the same thing, if it isn't ZDDP in reality.

Robin, I bet you're sorry now you asked about any of this.

lol

FEAR EXPENSIVE THINGS! RAWR!

Boxin' Robin wrote: ...what is your favourite motor oil brand and why?

Whatever Canadian Tire has on special.

Royal Purple.

Because it makes checking the dipstick fun and exciting! And because I get it for pennies on the dollar when it normally costs a first-born child.

beken wrote:   As well, when I went to buy oil at my local GM dealer, it was a case of Castrol Syntec in a box with a GM logo on it. The parts guy said that's what GM uses on all their cars with the exception of the Corvette, which gets Mobil 1.

GM also requires Mobil 1 in the Solstice GXP or you lose warranty - makes sense as the synthetic stands up much better to the heat of the turbo itself.  They don't have any provision for cooling the turbo once you shut down the engine, which surprises me a little.  On my Fiero, I have a reservoir of cool oil that bleeds through a metered orifice into the turbo bearing after you shut down to give it a chance to cool off.  It is the ash that forms when the oil stops flowing in the sometimes VERY hot turbo that is a killer.

You can certainly extend service intervals a bit with synthetic, and it is great for high mile/year cars.  I don't use it in the race car (you can't use it as a break in oil as it takes so long to allow an engine to finally break in you'd be into the next season!) and I don't bother in the Fiero, I just change every 3000 km or so.