Spark plugs
 

What should in a 1989 420 sel

Chances are that the plugs that came with the car are no longer made. You can go to the Bosch usa website and plug in your car to get a list of plugs as well as filters, O2 sensors, etc. Many people prefer the single electrode plug in Mercedes but I have been using the 2 electrode plug for about 2 years with no problems. If you want the single electrode scroll down as the multi-electrode ones are usually first.

Of course you could also check here at Fastlane parts.

Single and inexpensive copper for best bang for buck. Better metal for better life. Never go with multi-prong. Its all marketing and there are no proven gains. After all a flame front is a flame front. And there is this thing call physics that the marketing guys seem to ignore :)

I prefer copper (best conductor of electricity for the engine environment) NKGs. I will never use BOSCH plugs. They blow out too often. I also went a couple steps colder.

I seem to do fine with Beru - basic, cheap, copper plugs.

I've also used Bosch but the basic copper ones seem hard to find now.

NGK are excellent too, I hear.

Also, leads, distributor cap and rotor should be MB original if possible. My leads are Beru and they seem good.

My motto is, "Don't economise on HT components".

RayH

If you go to a racing plug,they are copper and non resistor.

Auto Zone claims that the Bosch Platinum Plus are the best for my car.

Should I install thes plugs?

You may. They are only better in longevity. Replacing plugs every year can wear on the plug threads in the head more. Personally I dont care. I prefer to replace plugs more often since inspecting them can tell a story. But if you are not into replacing plugs every year or so, go platinum, etc. for longer life.

Dont.
 

I used on my 560 sec,after 10 minutes I trow them away.

NGK BP5ES if I recall. Autozone or oreilly have them .

Those are what I'm running in the 420SEL.

Platinum's are all resistor plugs AFAIK. You already have a resistor in your spark plug connector, hence the need for non resistor plugs. Skip the platinums and follow the guys recommendations for one of the other good choices.

Don't get the Platinum ones, or Bosch. I had the same kind from Autozone and they were for crap. Went with $2.00 non-resistor copper and the car loves them!

420 benz, refer to your Owner's Manual for the proper spark plug. If the specified spark plug is no longer available, then rely on a cross-reference chart from another manufacturer to select an equivalent spark plug (heat range and seat configuration). Be sure to use a light coat of anti-sieze paste on the threads and torque properly, so as not to strip the head.

Most newer plugs have a coating which eliminates the need for anti-sieze compound. I know this is true of Bosch probably other major manufacturers.