Spark Plug advice please ?

[Pcn1]

1998 SL320 IL6 M104. (But I have document in the history file saying my car rolled of the line in 06/1997 if thats true I dont know)

My original MB owners books do not state the spark plug type.
Current plugs are Bosch with 3 electrodes but I forgot take any details of it when I had it out.

Just called local MB dealer and they want £66 for a set of 6 (ouch...) but wont tell me the spec obviuosly so I dont shoip elesewhere cheaper.

NGK web site Offer 2 types, upto 06/1996 BCP5ES (Cheaper normal plugs), after 07/1997 they state the 3 electrode type BKUR5ET.

So I could be right on the cross over point.

As the BKEU5ET are are around £8 retail, and I have 3 electrode type fitted by a decent indie garage last time (though thats not to say they got it wrong) Im thinking thats the safe bet.

Any thoughts ?

Thanks

 

[flowrider]

Stick with what you have, 6 plugs for £66 doesn't sound bad, i replaced my spark plugs last year and needed 16!.

 

[grober]

The 3 electrode plugs were designed for the later V6 M112 engine IIRC in turn they were replaced by the superior long life iridium plugs. So I would go for the early simpler BCP6ES or splash out on the later iridium plugs BCPR6EIX
NGK Partfinder

 

[ashenfie]

Based on the Vin number the MB dealer should give you the correct plugs. I would stick with the MB factory fit ones as they are not like any normal plugs. Most likely the factory fits will be single electrode type , but will be correctly gaped and avoid any odd miss fire issues that can result by using other plugs.

Fit the plug is a real pain and need a air gun/can to clear dirt before remove the plugs. Getting the coil packs off and extenders is quite tricky and needs to be done with care.

 

[Joesoap17]

Check on Sparkplugs UK site it shows the cross reference for standard/oem.
As to MB plugs they just get them in from Bosch or Beru and put them in the engines on assembly line straight from the box.
So buy whichever equivalent is best value.
Preferred wisdom is buy copper and change often 1-2yrs or buy iridium and change very 6 yrs

 

[ashenfie]

The plugs in/out and put in my merc looked like attached (as you see not quite your normal plug) and I think are made by Bosch. Manual says 40,000 miles or 4 years. Other plug can be used and may well work ok. I have run into issues with miss fires and non oem plugs on other cars. I purchase mine with a MB dealer via eBay.

 

[Joesoap17]

I tend to use NGK for cars and bikes never had an issue with them.

 

[grober]

According to Sparkplugs UK site there was a period 07/97 to 05/98 when the 104.991 straight six ran a hotter plug 5 instead of 6- don't know why this might be? except perhaps to meet certain emission standards and the later cars have a different advance curve in the ECU?* These are listed as the 3 electrode BKUR5ET and the iridium based BKR5EIX
Your car would appear to miss that window ---just----- meaning its possibly best to run one of the cooler "6" plugs given the choice between two heat grades of plug the cooler plug is safer as hotter running plugs are more prone to pre-ignition
https://www.ngk.de/fileadmin/Dokume..._in_download_area/ngk_zuendkerzen_code_en.pdf

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* mercedes were about to phase out the straight 6 M104 in favour of the V6 M 116 but the M104.991 engine was to soldier on in the W140 S class saloon till 99 I will guess there were some mods to the engine because of this W140 model and the runout straight six SL 's got the same mods??


ps altho

 

[Pcn1]

Grober,

Thanks for that info, much appreciated. Ive done some more digging with a VIN check of the web and its turning up 28/07/97 as the delivery date (yet again, if thats to be belived)
I think even some of the internet souces may get things wrong. I spoke with a reputable ignition parts seller yesterday, gave them my reg number and they pulled the vin code and from their ref data base told me Im running the M112 V6 engine, I said nope, its defo a straight 6 !
Seems you have to be a bit of a private detective to hunt down the right parts for older cars.

 

[grober]

If the car has any MB service history/invoices from its early days under warranty when it might have beeen serviced by an MB dealership it might just detail any plug type used back then?

 

[ashenfie]

I can be quite hard sometime to know what engine is installed. The M112 is a V6? So for it to be a straight 6. I think it replaced the M104 which was a 6 inline engine. So that the engine you have?

 

[Pcn1]

I have the inline 6. The V6 was fitted from 1999 I understand.

 

[Pcn1]

After much thought, Ive bitten the bullet and done something I dont normally do....order parts from the main dealer !
Theres too much confusion about the correct plug for my car as it seems to have rolled of the production line the very month MB changed the plug spec.
So in a perfect world only MB's data base will have the correct details. Im paying £59 for 6 plugs so they had better be the 3 electrode expensive type !! And going forward I'll be able to buy a NGK spec online.

Pick them up tommorow. Thanks to everyone who chipped in with advice.

 

[grober]

After much thought, Ive bitten the bullet and done something I dont normally do....order parts from the main dealer !
Theres too much confusion about the correct plug for my car as it seems to have rolled of the production line the very month MB changed the plug spec.
So in a perfect world only MB's data base will have the correct details. Im paying £59 for 6 plugs so they had better be the 3 electrode expensive type !! And going forward I'll be able to buy a NGK spec online.

Pick them up tommorow. Thanks to everyone who chipped in with advice.

Please let us know which plugs MB supplied make and number {the plug number that is}

 

[ashenfie]

After much thought, Ive bitten the bullet and done something I dont normally do....order parts from the main dealer !
Theres too much confusion about the correct plug for my car as it seems to have rolled of the production line the very month MB changed the plug spec.
So in a perfect world only MB's data base will have the correct details. Im paying £59 for 6 plugs so they had better be the 3 electrode expensive type !! And going forward I'll be able to buy a NGK spec online.

Pick them up tommorow. Thanks to everyone who chipped in with advice.

I know many like the 3 electrode type, but IMHO and experience they don't last any longer, 3 sparks = 3 times as much ware and does exactly the same job no better and no worse.

Iridium will last longer but again cost more. £60 on the right spark plugs every 4 yrs (think that right for the M104) not really that bad.

 

[190]

I know many like the 3 electrode type, but IMHO and experience they don't last any longer, 3 sparks = 3 times as much ware and does exactly the same job no better and no worse.

You only get one spark with a 3 electrode plug or any multi electrode plug. The spark will choose the path of least resistance and in the long term even out the wear across all of the electrodes.

I used 4 electrode plugs in my 190e and while they lasted a long time for a non precious metal type of plug, the engine ran just as well using normal plugs.

 

[markjay]

You only get one spark with a 3 electrode plug or any multi electrode plug. The spark will choose the path of least resistance and in the long term even out the wear across all of the electrodes.

I used 4 electrode plugs in my 190e and while they lasted a long time for a non precious metal type of plug, the engine ran just as well using normal plugs.

Correct.

The 4-electrode Bosch plugs on my Vauxhall Omega had an 80k miles service interval.

The single-electrode NGK Iridium plugs on my Toyota Previa had a 66k miles service interval.

 

[ashenfie]

Correct.

The 4-electrode Bosch plugs on my Vauxhall Omega had an 80k miles service interval.

The single-electrode NGK Iridium plugs on my Toyota Previa had a 66k miles service interval.

I think there is more to it than the number of ground prongs. A manufacture service intervals are based on the test data and safe margins baised by massaging the 'cost of ownership' figures for fleet buyers. We all know how true those sealed for life gearbox stickers are.

 

[grober]

Still waiting to hear which plugs Pcn1 got from his MB dealer????