MR500SEL

I was looking into how much effort would be required to change the spark plugs in my 84 500 SEL. During my probing I removed one of the spark plugs and was surprised to find that the tip of the spark plug was not there – just the thread where the tip would have screwed on. Is this correct? I can’t tell if the tip is stuck in the wire housing or if the correct way to install plugs in this car is without the spark plug tip. ???

Also – I was planning to use the standard Bosch copper plugs (Bosch Super – 7505 W 8 DC). Seems like several threads have cautioned against using platinum type plugs. Is this correct? Is the recommend gap of .032 the way to go? One thread suggested .034 - .036

500MPL

On the '84 500SEL the copper WDC 8 is what is suggested for the car. Also, the tip of the plug that is sleeved into the plugwire is correct as being just the top threads. Bosche makes it possible to use plugs in the two different ways. New plugs will come with the tips either screwed onto the plugs or just in the box. Make sure to use anti-seize paste on the threads going into the heads of the motor. Make sure to use a click style torque wrench and secure to 12lbs. This will give you a consistent depth on the new plugs. Also maintain the gap at .032, and DO NOT use platinum plugs in the 126-037 with 117.963 motors. It's a waist of money and the car doesn't run well with those plugs.

Good luck.

m117968

Actually, MB released a TSB calling for the W9DC' (heavier electrode) as high speed cruising can cause the 8's tip to get too hot and cause pre-ignition. I have spent a fair amount of time on an oscilloscope I have hear at home and have found the best results w/ my plugs gapped at .42. You may also want to make sure your cap and rotor are in good shape. If you don't know when the wires were done last it would be a good idea to replace them, w/ that in mind, the nicest wires I have come across are the Beru's.. The Bosch units are not what they once were...

Best,
Jonathan

Untertürkheim

I know this is an old thread, but this information is always relevant.

I just had my 1988 560SEC serviced, and among the plethora of items replaced were the spark plugs.

I had the Bosch Platinum IR Fusion (4-ground Platinum/Iridium Spark Plugs) (Part # 4507) installed instead of the standard copper cores the dealer was going to use. These plugs are really amazing, I am getting better fuel economy than ever before and the engine is literally smooth enough to balance coins on the cam covers.

I did think this over for a long time, and one thing I did realize is that by having 4 grounds instead of one, and more conductive materials (iridium) there should be less heat generated from electrical resistance, and better heat dissipation with these Ir 4 ground plugs than with the original single ground copper plugs.