Spark Plug Question/Clarification

[yogiysh]

I'm a bit confused about the choice of spark plugs for my 280 se 3.5 L.

At the moment it runs well on Beru 14 8 DU (equivalent to Bosch W8DC ...I believe) but the time has come for my first general tune-up.

In reading some of the past postings for a 4.5L, it was recomended to use the Bosch W7DC plugs. Firstly are the spec requirements the same in both motors in the ignition department (i.e. spark plug gaps and contact point gaps, etc)? Secondly, the question of hot plugs and cold plugs - why would hot plugs be used? The Beru 14 7 DU (~Bosch W7DC) is recommended by one MB spare parts dealer then another recommends Bosch W9DC. The current plugs used falls in the middle of the two. Which one of the three should I choose?

Please note I only use 98 octane unleaded with fuel additive for the valves lubrication because Tobias runs really well on it. The standard fuel just makes the engine run noisier and a lot less power.

Now spark plug gaps. The MB CD says it should be 0.5mm but past posts advise 0.028 which is 0.7mm. The current gap on the plugs being used is 0.7mm. Should I just stick with 0.7mm?

Looking forward to your advice.

[Tomguy]

I know the manual(s) that came with your car probably say 0.023" (0.5mm?) spark plug gap - but 0.032" (0.8mm?) is the proper value. Running 98 is a GOOD thing on the 3.5 - it has high compression, and lower octane tends to ping a lot on it. Since it requires a hotter spark to ignite higher octane fuels, I would suggest the W7DC (the hotter one I believe, but if it's the 9 that's hotter, use that). Hotter plugs can reduce pinging and incomplete combustion, as well as warm up to their self-cleaning temp faster for easier starting and better idling. The original suggestions for the 8 are taking 2 things into account: 1) longer plug life (colder spark in a hotter than avg chamber to lengthen life) and 2) Lower grade fuel doesnt need as hot a plug. I say since you're a DIYer, plug life probably isnt as important, plus modern plugs tend to last a lot longer than the originals.

[psfred]

TAke a good look at the insulator tips when you change them. If they are nice even gray or tan, you have the correct heat range. If they are dark brown, you are either rich or too cold, if blistered too hot.

Chances are what you have are working fine and I would not change heat range.

Peter

[Gilly]

MB calls for Beru 14-7DU or DUO on this engine, I'd prefer the original Bosch W7DC or DCO, gap should be .8mm. (Champion N9YC or YCC is another recommended plug.)

Gilly

[yogiysh]

You're right Tomguy the CD specifies 0.5mm and thank you for the explanation - it makes more sense now.

Pfred I'm looking at the plugs right now (thanks to wireless technology, I've got my computer in the garage - all I need now is a digitall camera so that I can post the conditions of the plugs) and they are all grey to a light reddish brown. Very fine deposit on the tips of the electrodes, no blistering and in looking at the whole set they look pretty consistent in their colouring and conditions. So it looks like all the cylinders are performing similarly (but I haven't done a compression test on this engine though). Could the reddish brown deposits be contributed from the 'Flash Lube' additive?

"If it aint broke don't fix it!" - so I will take your advise and go with what's currently being used.

Now back to the gaps, the current ones are set to 0.7mm, now it's advised to set it to 0.8mm - would 0.1mm make a big differrence?

Thank you everyone for all the wise advise ...

Cheers,

Ysmael

ps - I've attached a scanned picture of Tobias on the delivery trip from Melbourne. Sorry for the poor quality but will post better ones after I invest in a digital camera.

[psfred]

More gap may and may not make a difference, it does on some engines (better spark at low speeds). No idea what it will do for you, but it probably won't hurt.

Reddish color is from manganese in the fuel (to replace the lead), no longer used in the US, but I remember it. Harmless, what you should be worried about is signs of overheating or mixture problems, and it seems as if you are fine on both counts.

Peter

[yogiysh]

Thanks Peter, I'll try thr 0.8mm gap on the next set of plugs. Just finished replacing them as well as a new air filter ( I nearly fainted when they told me the price - AUS$ 70.00 for a Mann airfilter) and Tobias is driving really well !

I've just done my first oil change on a Merc and I love concept of just replacing the filter elements. Thanks to all the previous posts as well as your contribution to them, it made so simple ! ...even the long one about "which way is up" - symantics.

I'm waiting for the contact points to arrive as well as a speedo cable before I even contemplate the timing (yeh, the speedo finally gave up). Here's where I nearly did have a heart attack (I have a habit of checking with Mercedes Benz first), I was quoted, get this, AUS$690.00 plus postage and handling from Germany coming to a grand total of AUS$830.00 (tax incld) !
After peeling myself of the floor, I managed to call MB Classic Spares Dealer in Canberra and they're sending me one a new one (GEMO brand) for AUS$72.50. I think I've finally broken this habit!

As for the timing, it feels a little advanced but I'll check it when can get a hold of a dwell meter and timing light. This might be another posting...

Peter, thank you again and to everyone else that contributes to these forums. I've never had so much satisfaction in DIY car maintenance before!

[nachi11744]

Hello,
Nice car, if you ever think of selling....drop me a line. One of the fastest four door saloons to come out of Germany in the early seventies:0-60 in 9 seconds and 128mph top speed with 16 mpg fuel consumption.

[yogiysh]

Thank you, I'll keep you in mind - at this stage I'm really attached to Tobias - it's my first MB and first V8 and I can't see no other alternatives.

I do really like the feel of this car on the road especially on the freeway and country roads. It's got lots of legs and keeps on going, these engines are superb - can very easily loose my licence whilst cruizing.

There was one for sale in Canberra exactly the same colour, year and model but in concourse condition for AUS$20k and another (non concourse but immaulate) still available here in Sydney but in an Ivory/cream white (if that makes sense). Let me know if you want any details, I can always refer your interest.

Cheers,

Ysmael

[nachi11744]

Hello,
Perhaps you could send me a *private message* with the details of the other two cars, I need RHD and something over 25 years old to qualify for the *classic roadtax* here in Malaysia
Have a good week.

[230/8]

Spark plug recommendations can vary widely depending on who you ask, or in this case, didn't ask. My personal preference is the NGK BP6ES. Has a nice wide heat range, stays clean and works like crazy at .030-.035 gap. I have used Champs, Bosch and NGKs in my 230/8 and 350SL 4.5 and much prefer the NGK. Cost is about the same regardless of brand. Stay away from platinum unless your ignition was designed for them, and it was not.

For what it's worth...

230/8