Unleaded Petrol

[Grant V]

Gents,
I'm running my 6.9 on lead replacement. What must I do to the car if I want to run unleaded?

[Andrew280SEL]

Hey Grant,

Are you talking about valve strengthening and all that? As far as I know theres nothing you really need to do. If you really want to be careful you use that Octane raising additive stuff, but MB supposedly said any post-war merc is fine for unleaded. Is this what you meant?  

[john skene]

I believe that after 1976 the valves are hard enough on Australian and USA delivered V8 cars for straight unleaded to be used. We printed the list (supplied by Mercedes) of cars suited to use unleaded fuel in the NSW club magazine about 5 years ago, has anyone still got a copy?

[Andrew280SEL]

It wouldn't surprise me if Oscar manages to dig up it up 

[Grant V]

Um...from what I understand, if an engine was not designed for unleaded, unleaded can eventually damage the valve seats. But maybe the 6.9 had already been designed with unleaded in mind, and it might just be a matter of changing the timing? (My car is a Euro spec BTW) Or would i have to remove the cylinder heads to get compatible valve seats fitted? In which case I'll just keep running with lead replacement petrol.
However, unleaded is cheaper tha LRP, which...err....sort of comes into the equation when filling a 6.9

[Andrew280SEL]

Yeah, I can see your thinking Grant, I was wondering at first too, but MB seem pretty adamant that any car post-war is fine because of the already hardened valve seats. Any car after 1976 is DEFINITELY fine for unleaded, as they made the switch in that year. But even if yours is pre-76 I don't think theres a major problem. You might consider an additive if so, as for the timing though, I'm not sure about whether the cars over at your place are different in compression or timing etc.

[WGB]

It would be interesting to compare part numbers for Euro vs Oz vs USA heads and if they are the same we would really know that the seat hardening was uniform.

I do not know if the changes in compression ratio between the three engines were in the pistons or the heads but I assume it would have been in the pistons and that the heads may have been uniform.

I have had no problems running my 8.8:1 compression Euro 450 on unleaded but it does like 98 RON.

Bill

[Mforcer]

In my very humble opinion, I would only believe the Classic Center which have stated that no lead additive is required. I use lead free without any additives.

It would seem logical to me that MB Australia simply would not advise specifically about engines that they did not test and I doubt they did any testing. It would be more prudent for them to advise owners not to change the fuel the engines were originally advertised for, not what they were designed to handle.

Why is it that only MB Australia have advertised lead replacement additives for use in older cars? When did other countries stop using lead in fuel? I doubt Australia would have ever had soft valves while other countries had hardened valves?

Also, does compression ratio play any difference for using lead in fuel? I thought that only determined the octane used.

[WGB]

The CR was only mentioned to see if there might be a similarity in heads for different markets.

If the same head is used in a e.g. Euro as in an Oz head you can get a further dimension of objectivity about unleaded suitability.

It's only octane that matters with the CR. But an Oz 8.0:1 is more likely to be happier on 95RON than an 8:8 :1 Euro (117 motor anyway).

Bill

[Grant V]

I'm open to correction here, but I think that lead was added to petrol because of it's anti-knock properties. The higher the compression ratio, the more the engine is inclined to knock, which is offset by using a higher octane rating petrol. A higher octane rating was achieved by adding more lead to the petrol.

[Grant V]

Mforcer,
South Africa has been pretty late with petrol changes, with unleaded only being introduced three (?) years ago, and leaded only being withdrawn from the market in January last year. Leaded was replaced with Lead Replacement Petrol, which is what I use on the 6.9.
Long before unleaded was available in SA, in the late 80's even, all MBs here, whether locally produced or imported, were already set up for unleaded, but tuned for leaded petrol. If I remember correctly, the 560SEC had a round switch in the engine compartment that was turned to different setting if unleaded was used.

[Andrew280SEL]

***I PREDICT OSCAR IS DIGGING INFORMATION AS WE SPEAK***-stay tuned 

[oscar]

 

mate I seriously just walked thru the door and I'm on to it

Tomi recieved an answer from the Classic Centre in Stuttgart that says:


Dear Sir,

Your question about the use of unleaded fuel is easy to answere:
All Mercedes-Benz cars (pre-war and post-war) have absolutely no problems
with unleaded fuel.

We recommend to use fuel with an octane rating of 98 (ROZ) for every type
and also a regular
control of the valve clearance, twice as much as specified by the factory.
In our experience no additional lead substitute additive is necessary.

A normal use of the car is required, of course.

We hope this will help , please feel free to ask if you have further
questions.



Mit freundlichen Gr??en /Kind regards

Andreas Hosch
DaimlerChrysler AG
Mercedes Car Group
Brand Communications
Mercedes-Benz Classic Center
000/R051 - MK/CL
70546 Stuttgart
Phone: +49 (0)711 / 17 -8 40 40
Fax:      +49 (0)711 / 17 -8 34 56


Clicking on the above response will take you to Tomi's original post and his question that was posed.  I think John Skene's comments are spot on regarding early V8's like my 350 that weren't included in the MB AUS list of cars not needing an upper head lubricationg additive.  I never personally found anything that listed early V8's in the "all post war mB engines list" which was on the MB AUS page.  Anyway, sometimes I use it, sometimes I don't.  My early V8 has had all sorts of fuels: leaded up till 1993 approx, then LRP, then from 1997 approx onwards - 91RON unleaded with no additive. 

In previous ownership, without additive and on 91RON unleaded fuel, it's done more km like that then what some lesser cars do in a lifetime.  Approx 200,000km.

Just use 98RON I reckon GrantV.  Upper head lube will be a personal choice.  I know styria uses it. 

Either way, no need to go to the expense of putting new valves in yet.  Might as well burn the old ones first   IF that's what's going to happen which I doubt will.

[13B]

I've now driven a full tank of E10 and a full tank of Premium unleaded.  Didn't notice any difference.

True to the IT industry I work in, I've finally read the paperwork/manual which came with the car after covering some considerable distance... (we call that RTFM - trying something out and then looking at the manual).

Very officially, the brochure says the car will run on 91RON, what with being the 8.0:1 CR / 198kW version.

Therefore I'm going to try and tank of plain old unleaded when i fill up this sunday.  I figure if the car hates it, I can syphon it out and put it in my wifes Verada and my RX7). 

Will post what I find after sunday..

[Grant V]

Thanks, guys. I'll start running 98 Unleaded and see what happens.
Any malfunction or $$$ spent will be covered by Oscar....