I would like to get an opinion and some help. I have a 1992 300-E M103-983 six cylinder . The car has 37239 miles only. When is the approprate time to change the spark plugs? I got the Bosch super H9 DCO 0 241 225 573 spark plugs from flast lane. The engine is not missing or having any starting problems.
Should I wait to a certain milage before replacing the plugs.

What is the gap these plugs should be set at? I have the Hazet puller so not to damage the spark plug wire ends and the factory spark plug tool to remove the plugs. Also what tork is approprate to seat the plug cold when doing the service. I cannot fine this information in my engine factory manual.

Thank You
Bob Geco

the torque is on the box the plugs came in 20NM i believe, the gap i use is 0.040 of an inch, the plugs are recommended by mercedes every 15 thousand miles.

The plug gap recommended by Mercedes is the same as the plugs are manufactured--you'll note a gap specification on the box.

You can check them before you install them but they will all be perfect unless a box was dropped. This of course applies to Bosch plugs, only.

Ignore "inch" gap figures and use metric gap figures as befits a German car.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

The recommended spark plug gap for all emission controlled engines is listed on the emission control label in the engine compartment, so there is no need to guess.

For my M103 it is .032" and I believe all other M103s are the same.

H9DCs or DC0s should be gapped at about .032" out of the box, but they should always be checked prior to installation.

The recommended replacement interval is 30K miles for 49-state cars, but MBNA recommended 15K miles for some CA models as a hedge on the emission warranty.

The recommended tightening torque in the M103 engine manual is 20 NM, which is .72(20) = 14.4 lb-ft = 173 in-lb, but I use 150. Most OEMs recommend in the range of 10-15 lb-ft for 14mm taper seat spark plugs in aluminum heads.

Duke

Duke.
I took a close look at the big yellow emission lable. It says reguarding tune up specifaction except for timing and idle to see manual? So I re set the first three plugs to 032. the next two and last plug are going to be a bear to remove because of the close proxcimity to the fender apron.
By the way we need to get together so I can give you back your towel I have been guarding all this time. Lets get together for dinner after the holidays.

Wish me luck:
Bob Geco

I thought the EPA required the plug gap to be listed on the emission tuneup label, but mine doesn't show it either, so I guess I'm wrong on that thought.

The plug gap is listed in the owner's manual - inside rear cover - "What you should know at the gas station". Tightening torque is listed on P81 (see owner's manual index for your car) under "Spark Plugs" - 10-20 NM (7-15 lb-ft). Like I said before, I use 12 lb-ft, which is 144 lb-in or .72(12) = 8.6 NM.

We should get together and flush our power steering systems as soon as we figure out what fluid to use. System capacity listed in my owner's manual is one liter (1.1 qt) so 1.5 to two quarts should do a good flush.

What's the PS system capacity listed in your owner's manual?

Duke