Again on spark plugs

[dante53]

I cannot get it clear!
I read that many suggest Bosch W9DC or NGK BP5ES spark plugs on w113 engines.
The original spark plugs suggested by my owner manual are Beru D250/14/3 S and Bosch WG250T28. The same spark plugs were original equipment of 250 SE and 280 SE in the same years but they are NLA and probably are obsolete anyway.
They are very cold spark plugs, comparable with Bosch W4/W5 series and NGK BP8 series: a lot colder than Bosch W7, W8 and W9 and NGK BP7, BP6 and BP5 usually suggested.
I understand that old fuel injected engines usually run rich and with lower compression than when new but, taking into account that WG250T28 is a non projected spark plug and that newer spark plugs are generally projected ones (more efficient in igniting the mixture in the compression chamber), it seems to me that up to three temperature grade hotter than originals is really a too heavy jump!
I must replace the old Bosch W7DC actually installed on my engine and i really do not know what kind of spark plug I should install.
The only exact match with WG250T28 I found on the web, according to conversion charts, is NGK BP8EVX, which is a platinum spark plug.
I think that BP8ES would also be an exact match. So, BP7ES, just one step hotter, would be an acceptable compromise.
What is your opinion on this?

Dante

1965 230 SL
Italy

[GGR]

Well, gas is also different nowadays (no lead, some ethanol etc.). Apparently engines run better with a bit hotter spark plugs with nowadays gas. Also engines sold in the US had hotter spark plugs than in Europe on some models. So I don't know. W7DC seems a good compromise, though you may have to go to an MB dealer to get them. In any case, don't fit resistor spark plugs.   

[badali]

I just bought a box of W7DC on ebay.  There are more available on this listing...

http://www.ebay.com/itm/171141929535?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[J. Huber]

...I read that many suggest Bosch W9DC or NGK BP5ES spark plugs on w113 engines.

Dante

1965 230 SL
Italy

Hi Dante, I think you may have answered your own question there -- experience seems to show that these two plugs work well for most broken-in but robust 113s.

A set of these, together with the correct spark plug wires, a good red coil & 1.8 resistor, and new points properly set (or electronic I suppose  ) and you should be on your way!

[Benz Dr.]

I now use BP5ES which conforms to just about every engine I work on. I would only go to a 6 if signs of running too lean were evident.

[dante53]

My old W7DC look quite good. No signs of rich running

[jameshoward]

My old W7DC look quite good. No signs of rich running

So... do you need to change them? Give them a brush, reset the gaps and continue using if they look ok.

[garymand]

If you want opinions...we've got them. 

If you want clarity about what works best in your engine and under your driving style: 
buy one W9DC, one BP8ES, one BP7ES, and one BP5ES. 

Intall them in place of 4 of your current plugs.  After a 50 mile run of your typical, or prefered, driving style, pull all 6 plugs and see what looks best your your motor. 

Then you can give us the facts relative to your motor and how you drive.

[dante53]

James, they look good in relation to fuel ignition but they are worn so I will need to change them soon.

[Paul99]

errr.... this is getting confusing.

NGK plugs - the numbers go SMALLER=HOTTER - larger=colder, and they are all resistor type.

http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp?mode=nml

I have tried BP6ES, and getting a bit of fouling so a BP5ES might be better.  But I also get a bit of pre-detonation so was going to try 7's.    So I guess the "try them all and see which one is best for specific engine" is the way to go!

Some suggesting NON resistor type.  All these NGKs are resistor type.  ??

[jameshoward]

All the NGKs you've quoted or which have been quoted to you are NON resisitor type. Basically, don't buy any NGK or Bosch plug with an 'R' ('R' = Resistor; eg WR9DC) in the spec and you'll be fine.

[dante53]

I replaced my old W7DC with NGK BP7ES. Old plugs present moderate signs of fouling (velvet soot)  but the overall color is a dark brownish one. So, if I'm not wrong, I think they were jut a little bit colder than optimal. As NGK BP7ES are colder than W7DC I expect that they will present even more soot when i will inspect them. Nevertheless, old plugs were worn, ran most of their life with points, an old blue coil and a way out ignition timing, while new NGKs will run from the beginning with electronic points, a brand new red coil and a more reasonable timing. So, let's see what happens.
If they should turn out to be too cold as I expect, I will replace them with BP6ES or BP5ES, depending on the amount of soot I will find on them.
In such case BP7ES will replace the Bosch W5DC installed on my 911 so nothing will be wasted.