Sulfated ash

[mjoekingz28]

Is a higher number of sulfated ash always bad? Does it depend on a lot of scenarios?


This would be concerning DOHC and OHV gas engines.

 

[mjoekingz28]

My mistake, I put a space after the colon when searching this site thru google and got no real feedback. I eliminated the space and have a lot to read through now.

 

[mjoekingz28]

Now that I've brought it up. Does synthetic oil burn less cleanly than dino? Maybe syn resisting burnoff is undesirable in an oil burner and can leave more or more harmful deposits than a simple conventional that is free-er to burn-off.

 

[Alex_V]

Originally Posted By: mjoekingz28
Now that I've brought it up. Does synthetic oil burn less cleanly than dino? Maybe syn resisting burnoff is undesirable in an oil burner and can leave more or more harmful deposits than a simple conventional that is free-er to burn-off.


I have no scientific evidence but I've thought the same thing.

 

[d00df00d]

Originally Posted By: mjoekingz28
Is a higher number of sulfated ash always bad?

Pretty much.

Originally Posted By: mjoekingz28
Does it depend on a lot of scenarios?

Different factors can affect how bad it is; e.g., it's much worse for a modern diesel engine with sensitive emissions controls than it is for a catless gas-burning race engine. It's never a good thing, though.

At best, it's tolerable as a byproduct of a necessary additive. But it's always bad to some extent. If you can minimize it without bad effects, that's the best thing to do.

 

[d00df00d]

Originally Posted By: mjoekingz28
Now that I've brought it up. Does synthetic oil burn less cleanly than dino? Maybe syn resisting burnoff is undesirable in an oil burner and can leave more or more harmful deposits than a simple conventional that is free-er to burn-off.

I've heard that SOME synthetic basestocks can leave really bad deposits when burned, and that's why Mazda wanted to err on the safe side by recommending only conventional oil in their rotary engines (which burn oil by design).

Don't think it's an issue any more, though.

 

[SR5]

Originally Posted By: d00df00d
Originally Posted By: mjoekingz28
Now that I've brought it up. Does synthetic oil burn less cleanly than dino? Maybe syn resisting burnoff is undesirable in an oil burner and can leave more or more harmful deposits than a simple conventional that is free-er to burn-off.

I've heard that SOME synthetic basestocks can leave really bad deposits when burned, and that's why Mazda wanted to err on the safe side by recommending only conventional oil in their rotary engines (which burn oil by design).


Yes, I've heard the same thing about rotaries. However, I would have no problem running a Group 3 synthetic, because it's just a highly purified and HydroCracked Group 1 or 2 oil.

 

[HerrStig]

Aircraft turbines are total loss engines which use synthetics, and synthetic 2 cycle oil is very popular. That tells us something. Also, most synthetic has fewer additives than conventional to maintain grade and so may cause fewer deposits. It may come down to how cleanly the base stock burns.

 

[d00df00d]

There are plenty of rotary folks who run synthetics that are heavily group IV or V.

IIRC, what I heard was that the problem was only with one specific type of synthetic basestock that wasn't even found in a majority of oils at the time. It was just impossible to tell which oils had it and which didn't, and Mazda didn't feel like going to all the trouble to validate a ton of oils or create a whole new spec when decent conventional oils worked just fine.

Gotta say though, I got none of this from an official source and I can't even find where I originally read it, so please take it with a fistful of salt.

Either way, I can't imagine it's a big problem. I definitely saw Mola Kule here say most synthetic basestocks burn nice and clean, so if it ever was a problem for rotaries, it likely isn't any more.

 

[weasley]

Originally Posted By: d00df00d
Originally Posted By: mjoekingz28
Is a higher number of sulfated ash always bad?

Pretty much.

Bad for what? If you are running a big old diesel engine on high sulfur fuel, you're going to want that sulfated ash as it represents detergent (and hence TBN) content. If you're running a DPF then you want less ash down the tailpipe, so lower ash oil is better. It depends on your needs.

Originally Posted By: SR5
However, I would have no problem running a Group 3 synthetic, because it's just a highly purified and HydroCracked Group 1 or 2 oil.

Not quite. Group III is not made by hydrocracking Groups I or II, it is made by hydrocracking a waxy material that is extracted from crude oil.

The Mazda thing came about because of a difference in what "synthetic" means. In Japan it is like in Germany - Group III is not considered to be synthetic. The missive from Mazda Japan was "don't use synthetic oil in the RX-8". The intent of this message was "don't use PAO in the RX-8". But of course everywhere else people interpreted it as "use only mineral oil in the RX-8". In fact the Mazda oil that they used to fill and service the RX-8 was, itself, group III. I ran mine on group III oil and it was fine.

 

[d00df00d]

Originally Posted By: weasley
Originally Posted By: d00df00d
Originally Posted By: mjoekingz28
Is a higher number of sulfated ash always bad?

Pretty much.

Bad for what? If you are running a big old diesel engine on high sulfur fuel, you're going to want that sulfated ash as it represents detergent (and hence TBN) content. If you're running a DPF then you want less ash down the tailpipe, so lower ash oil is better. It depends on your needs.

Slight but important distinction: what you need are certain properties, which are usually provided by ashy additives. That doesn't mean you want the ash per se. If you can get the same properties with a lower ash additive pack, you'll be better off: same functions, fewer harmful byproducts.


Originally Posted By: SR5
In fact the Mazda oil that they used to fill and service the RX-8 was, itself, group III.

Interesting. Source for this?

 

[weasley]

Word on the street back in the day (I'm talking 2004-ish) is that at least here in Europe the Mazda Dexelia Ultra 5w30 was Total Quartz Future 9000 5w30, which was clearly a Group III at the time (see here for some hints, but it looks like the trail has gone cold).