I've been thinking about changing my spark plugs while I'm changing the spark plug wires and perhaps the coil in my 190SL. I've read a couple of posts in this forum warning against the Bosch Platinum +4 (reportedly the best plugs for modern engines), and I was wondering why they would not be the best for the 190SL as well. Isn't having the greatest spark always best for combustion?

I have red / been told that 'platinum' plugs are not reccommended for-
1 older cars with standard ignition systems which may not produce enough voltage to fire them reliably.
2 some newer cars because the tiny platinum electrodes may cause misfiring at idle.

Having said that, I've been happy using Bosch Platinums (not sure about the '+4' designation) in my 1972 250 sedan for the past 10 years and Nippondenso Platinums in my 1987 Isuzu pickup for the past 7 years. Both vehicles have some type of electronic ignition with
a hotter ign coil than might be in a straight 'point' ignition system. If you can get them in the correct heat range and thread size it probably wouldn't hurt to try Platinums in your 190SL.

I have red / been told that 'platinum' plugs are not reccommended for-
1 older cars with standard ignition systems which may not produce enough voltage to fire them reliably.
2 some newer cars because the tiny platinum electrodes may cause misfiring at idle.

Having said that, I've been happy using Bosch Platinums (not sure about the '+4' designation) in my 1972 250 sedan for the past 10 years and Nippondenso Platinums in my 1987 Isuzu pickup for the past 7 years. Both vehicles have some type of electronic ignition with
a hotter ign coil than might be in a straight 'point' ignition system. If you can get them in the correct heat range and thread size it probably wouldn't hurt to try Platinums in your 190SL.
Good Luck, Mark DiSilvesto

I have heard the same thing. I think the reason is that "older" engines don't runas clean or as efficent as modern engines. If you have looked at one of these plugs, you will see there is not much of a surface area. The "platnum tip" is exactly that, a tip. As small as a fine ball point pen. These could easily be fouled out. Where as a traditional plug has a center electrode that has larger surface area. I haven't about the plugs needing more voltage to run, but that wouldn't surprise me. It the ease of being fouled up that I have heard before. Modern engines run much leaner (cleaner) than your 190SL was designed to.

Plugs
 

I helped a friend install them in his Audi and he loves them, I plan to put them in my Land Rover. I think they have a gurantee if they don't work they will refund your money.

The problem isn't the Platinum, it's the resistance. MB ignition systems use resistor-end plug wires. You have to be careful about resistor spark plugs, if the resistance gets too high (combination of resistor plug wire ends and resistor plugs) your spark can really start to degrade. If it gets too high, it won't fire worth a damn, and in wet weather secondary voltage could actually secure a path to ground that doesn't really include your electrode gap at all! I am fairly sure that Plat spark plugs on the market are all resistor plugs, I would feel confident about recommending Plat spark plugs if I knew they weren't resistor plugs. Seems an "R" in the plug number mears a resistor plug, never seen a Plat plug without an "R" in the plug number yet.....Gilly

Hemant … Bosch copper plugs work great in a 190SL. The 190SL has a resistor in the rotor and I believe a resistor in the plug connectors. The wires are solid copper and the plugs have no internal resistors. When in doubt, stay stock. The correct plug from Star Quality only costs $1.45 so why pay more.

Use Copper Plugs
 

Hemant,

Jim's right. Use the copper plugs, either Bosch or NGK. NGKs are BP6ES. I highly recommend against the plats, and so do many others. You will find that the techs on this board on more modern cars (like my '92 300E) also recommend against the plats in newer cars. I'm experimenting with the BP5ES as it's a hotter plug and it keeps my plugs cleaner. You can get them from Star or usually your local autoparts store can get them overnight if they don't have them in stock. The BP5ES I had to order from Fastlane - cost me $12 for 4 including shipping (before shipping was free!).