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  #1  
Old 05-05-2003, 09:26 AM
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Question W126 280SE: Leaded vs Unleaded Fuel - fact or fiction?

This is a question I have asked many technicians and received various answers. I have a 1983 Euro W126 280SE (engine number 11098922036922).

This has been running on leaded until recently, and has required lead replacement additives with every gas fill. A poll with virtually all independant workshops and technicians have yielded a "don't bother putting additives" based on:

1. Cars of that vintage that have switched without modification have had no problems,

2. Valve seat recession is bull****, and

3. No sense to change perfectly working valve seats until required i.e. damaged.

However, the local MB dealer has advocated a conversion before using pure unleaded.

Will welcome any light on this confusion!!?

Kenny

1983 w126 280se
1983 w123 200
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  #2  
Old 05-05-2003, 01:49 PM
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Leaded fuel creates a " cushion " between the valve & the seat.
Todays engines ( build to operate on unleaded fuel ) have induction hardened valveseats & stellite ( or sometimes sodium cooled ) valves, to cope with the abscence of lead.
You have three choices:
1. Add lead substitute,
2. Run the engines until you have valve recession,
3. Have hardened seats & stellite valves installed.
It's you call.
I can guarantee you, you will have problems, it's just a matter of time.
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  #3  
Old 05-06-2003, 12:53 PM
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I cannot be certain in the case of your Euro, but 1983 was long after hardened seats were implemented in the US.
Unleaded gas began in 1974, I believe. In 1978 it was mandated for imports, if I remember right. Anyways, are you sure your seats are soft?
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  #4  
Old 05-06-2003, 01:14 PM
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Hello,
Not likely for your car to suffer from valve seat recession unless you are regularly running down the PIE at 5000rpm, at least 8 times a day !
Valve seats on Mercedes engines are hard enough to survive on unleaded, my 1976 M115 is still running fine. Mercedes recommends that the valve clearances be checked/adjusted at half the normal interval, 10000km in your M110s case.
Have a good week.
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Old 05-06-2003, 02:10 PM
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The only issue with unleaded versues leaded fuel is detonation. If you can obtain unleaded fuel with sufficient octane to keep the engilne out of detonation, then don't worry about the valve seats.

Even vintage Amercian engines with non-hardened integral valve seats in the cast iron heads do not have a valve recession problem unless they are run very hard such as racing or truck duty, and then the engines only have to be run with leaded fuel early in their life as this will build up a thin lead oxide film on the seats, which will mitigate seat recession for the life of the engine.

Further, if you engine has an aluminum head, it has OEM installed hard valve seats already.

Duke
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  #6  
Old 05-06-2003, 09:15 PM
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Quote:
Originally posted by nachi11744
Mercedes recommends that the valve clearances be checked/adjusted at half the normal interval, 10000km in your M110s case.
Have a good week.
Exactly. The reason for checking ( adjusting is more like it ), is to make up for the gradual valve recession you will get. !!!
Sorry, but I remember the 70's and in particular Ford's problems.
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  #7  
Old 05-06-2003, 09:48 PM
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Not a problem running unleaded. MB has been using hardened seats since sometime in the late 50's to early 60's, possibly even earlier.
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  #8  
Old 05-06-2003, 09:57 PM
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Quote:
Originally posted by csnow
I cannot be certain in the case of your Euro, but 1983 was long after hardened seats were implemented in the US.
Unleaded gas began in 1974, I believe. In 1978 it was mandated for imports, if I remember right. Anyways, are you sure your seats are soft?
That is what I am trying to find out. The official local MB reply was to change them, implying that they are soft.

Presently I am still using lead substitute, although the gas I am using is 98 RON and should ameliorate the problem somewhat. However, I do think the problem of seat recession is real and not imaginary.

Kenny

1983 w126 280se
1983 w123 200
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  #9  
Old 05-06-2003, 10:22 PM
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kennysin

Re-read my point # 2.
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  #10  
Old 05-06-2003, 11:06 PM
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On the subject of " Euro ", I can tell you this.
I frequently visit Germany and, to my amazement, as little as 10 years ago, they were still able to buy leaded gasoline. We have not been able to do so in Canada for about 20 years.
At the same time, anybody with an older car ( 1980's ), qualified for a government taxrebate if they retro-fitted their cars with catalytic converters and hardened valveseats & valves.
Okay, enough preaching, time to move on.
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  #11  
Old 05-07-2003, 04:25 AM
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do a little reasearch on leaded fuel and you just might find out that lead has nothing to do with valve seats at all. When Dupont was looking for a way to raise octane and useing lead to do it was a way to get a patten where other formulars were not though they did the same thing.........
William Rogers.......
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  #12  
Old 05-07-2003, 10:50 PM
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I had read around the subject previously, and have come across a few articles describing the relation of lead to valve seats as another "conspiracy theory" propagated by oil companies for various reasons.

Unfortunately it is all unsubstantiated with no hard scientific evidence, hence this posting.

Presumably one way to test it is to run unleaded until something happens. However, I was hoping someone has already done that and have an answer. Always good to learn from someone else's mistake...............!!!


Kenny
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  #13  
Old 05-07-2003, 11:14 PM
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Lots of 280SEs in this country, running on unleaded for years
without any problems.
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  #14  
Old 05-07-2003, 11:35 PM
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Hello,
OK, you want to learn from others *mistakes*...........
I have in Malaysia my own and two brothers cars as follows, all running on unleaded WITHOUT any additives or valve/seat replacement.

1. 1976 W115 200
2. 1979 W116 450SEL
3. 1972 Alfa GTV
4. 1975 BMW 3.0Si
5. 1979 BMW 525
6. 1980 BMW 628CSi
7. 1982 Volvo 240 B21A

In the US, I ran a 1966 VW Karmann-Ghia (original heads and everything) on unleaded regular gasoline without any problems whatsoever. I always check engine compression on all cars that I own once a year and Ghia had 120psi when I got it in 1998 and left my ownership in 2001 with 115-120psi.

The valve seat recession issue only affects engines with cast iron heads where the seat is cut directly into the iron head, without an insert.
DB gasoline engines have:
1. sodium filled exhaust valve stems
2. stellited seats

The *official* line from DB was that all engines manufactured before 1985 (introduction of W124) cannot run unleaded without retarding timing and halving valve adjustment intervals. If the engines are being ruined by unleaded, how does DB explain all the W114/115/116/123s still in regular use in Germany with the Wurm catalyser?

If you are still not convinced, ask an experienced parts man to cross check the part nos. for the valve seats for the US market M110 and the ROW(rest of the world) M110. I would not be the least bit surprised if it is the same. I do know that ALL Alfa Romeo 4 cylinder twin cam engines used the same part no exhaustvalves and seats for all markets from 1970 onwards.
Have a good week.
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  #15  
Old 05-07-2003, 11:37 PM
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and then you can always consider methane-fueled, propane fueled engines which have never had any tetraethyl lead in the fuel. or compression ignition engines which also never had any tetraethyl lead in the fuel.

when you think on it that way, then you will see that valve seat recession is aggravated/accelerated by other aspects of engine operation not involving a fuel additive.

in the gaseous-fueled engine, the lube oil additive package was the most influential factor in de-accelerating valve seat recession. oh, and by the way, the gaseous-fueled engine is a severe service, heavy duty application engine. your auto engine is a light duty application.

does this help you?
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