Spark plug gap for 2.3-16v OEM plugs

[crhenkel]

I have found a set of Bosch H8DC spark plugs which were OEM for my 1986 Mercedes 190e 2.3-16v. I typically cant find these plugs anywhere but online and then they are usually old stock. MB doesnt seem to have any more left. The autoparts stores locally dont seem to even know that they ever existed.
I am looking to see what the OEM spark plug gap was supposed to be set at. Can anyone tell me what the original H8DC spark plugs should be gapped at?
Thanks.

[Ferdman]

Check your Owner's Manual.

[Hirnbeiss]

0.8 mm (.032 in) per Haynes, which also lists H7DC as stock plugs.

[crhenkel]

Nope, tried it first. No gap for the spark plugs in the owners manual.
It does call for the type of plug. It calls for a Bosch H6DC instead of the H8DC that the MB EPC calls for and says is no longer available. This shows a similar plug with a different heat range. Dont know which one is the best choice.

[crhenkel]

Thanks for the gap info. I also am finding that the OEM plug number can be different. I have found H6DC , H7DC, and H8DC all listed as the proper spark plug. The owners manual shows 6 as being the correct heat range, the MB EPC parts catalog shows 8 as the correct heat range on the plug. Haynes shows 7.
Anyone care to tell me what might be their best choice for my 2.3 16v? I was using H6DC, and now I have a set of H8DC on the way.

[Ferdman]

The Technical Data section in the Owner's Manual for our 4 MB automobiles lists the spark plug and gap, even the torque value for our 1998 E320. Guess that's an upgrade to the Owner's Manual for earlier models.

Check the Bosch website for information regarding spark plug heat range. For what it's worth I run F8DC4 spark plugs in our 1991, 1992 and 1995 E-Class cars per the recommendation of our local MB dealer's Service Department.

[Duke2.6]

My US Bosch catalog shows the H8DC for the 16V, but the Euro version may have specified a colder plug. (The lower the number the colder the plug.) The gaps for all this series of plugs for use on MB engines is usually listed as .032".

Given typical US driving conditions, the hotter H9DC that is specified for most M103 engines is probably okay for a 16V unless you drive the car very hard.

The OE plugs for model years beginning in 1988 for M102/103 engines had an "O" suffix (such as H9DCO) and this suffix indicated a larger center and ground electode, which theoretically improved plug life. These are perfectly acceptable for all model years if you can find them, and they were usually only available at dealers.

My experience with the H9DC on the M103 engine is that they have little wear at the recommended 30K mile replacement interval and will probably easily run 60K miles on a car that doesn't develop a fuel mixture problem or have excessive oil consumption.

In any event, it's important to use a non-resistor plug to avoid rough idle issues and possibly emission test issues.

Duke

[crhenkel]

Thanks for the help guys. I figure I will try the H8DC plugs that are on the way. I can find the H#DCO plugs fairly easy. Didnt know what the difference was, thanks. Sounds like I can stop trying to find the old style plugs and use the O plugs. I dont drive the car hard so I figure I can use an 8 or 9 temp plug. The manual says 6, the MB EPC says 8. I figure they are all at 0.032 on the gap so that is solved. I was not sure that they were all the same gap. Thanks for all the help.