M119.982 Spark plug heat range colder as the engine ages
 

A question for old timers. My M119.982 engine is pushing 172K. As the cylinders are accumulating carbon, thereby raising compression, would you place a colder spark plug to counteract any chance of pre-ignition?

Best place to start would be to read the plugs, but I don't have spark plugs that i can read right now, because they're all fouled up due to top engine cleaning.

But, as a general rule, should you go colder plugs as the engine gets more miles?

Seeing as how you live in a moderate climate I think you can get away with it.
Regards, Eric

No reason for a well maintained engine using the proper tier 1 gasoline to accumulate carbon.

What process did you use for your "top engine cleaning"...?

Well, I'm actually in NorCal now. My location info is old....

Btw, I don't have any pre-ignition issues. I'm just asking out of curiosity.

I've always used Chevr@n 91, but one of my cats had been plugged up (replaced in about a week), and it's probably caused some valve clacking. (All oil plugs are good.) For the top engine clean, I've used MMO through the brake booster, through the PCV, and water through the same two hoses. I'm now also pouring in MMO directly into the plug wells, with the piston just after TDC and the intake valve slightly open. Pouring the MMO that way, I can actually soak the intake valves. Plus, if there is any carbon on the exhaust valve, that should leak MMO slightly and soak.

All this activity has changed the spark plug appearance. The MMO actually didn't cause much change, but the water created a lean condition, so the plugs are a bit blistered.

Anyway, that's just all info for fun. My question is, do old engines benefit from colder spark plugs due to increased compressions ratios....

Well actually you cant get the correct plugs in the states. Bosch F8DC4's are the closest non resistor plug. The F9 non resistor used overseas burns hotter so if anything were running too cold and we have more stop and go, considering we are speed limited to 155 should tell you the engine isnt getting worked over like it should.

Back 40 years ago & farther...changing spark plug heat ranges on most engines was commonplace.

With the spark plugs of today, that isn't necessary at all!

Most older engines would use a "hotter" plug when the mileage got that high.

I think that is the case with plats isn't it? Aren't they very heat "rangey" I'm running them in my 93 4.2 M119 despite the fact that everyone told me not to, that they would ruin my engine, my car, my life, and they would cause my wife to leave me. Everything's still fine 5 years later.
Regards, Eric

LOL, it's so funny how people will warn you that you're making a gamble, abusing your car, just because you're using something not OEM specified.

Btw, what plug part number are you using?

Since I had my plugs out today on my 96 sl500 M119 to do compression checks today I figured I would change the plugs. What would you all recommend I was looking at bosch copper 7927,bosch IR fusion,bosch platinum+2,and bosch platinum+4,but I dont want to really spend $40 to $60 bucks on plugs. Its been running fine on these beru plugs in there now, they look good nice color. but the gap looks to big most are 42 to 46. I thought they were suposed to be 32?

I used the +2s. I honestly don't remember the part number. It was so long ago Iridiums weren't even out yet. I really like the very open ground electrode design of the +2s and
+4s, that is why I use them. I do believe the +2s are just as effective as the +4s though, so don't waste your money sonny, don't waste your bread Fred on the +4s.
Don't forget the spark plug wires! They do go bad and are all too often overlooked!
Regards, Eric

Thanx Eric, I ordered the plugs today from AZ. My car does not have actual plug wires just individual coils for each cyl with a spring loaded plunger that rests on each plug ......................................John........................:D

jsap, refer to your Owner's Manual for the proper spark plug (and gap) for your engine. Do not use platinum spark plugs unless they are listed in the Owner's Manual. Be sure to use premium gas.

You've got the coil on plug ignition! Sorry I missed that you have a 96. All the M119s in my life are older LH/EZL versions as are the ones owned by my buds, I sometimes forget that there are Motronic M119s too, sorry.
Regards, Eric