preferred spark plug for M20 engine?

[stuartinmn]

This is for my 325ix so I'm posting here instead of the tech forum...is there a preferred spark plug for M20 engines these days? I was doing a little searching online and the e30 boards seem to say the Bosch W8LCR originally specified for an M20 engine isn't available anymore but I found multiple places still selling them.

[John in VA]

I, too, see them at Bimmerworld ($3.99), Turner/ECS ($6.79), etc. Maybe they've become available again in recent years.

[Aldo525]

NGK is "preferred" by BMW engines...M20 could be NGK ZGR5A

[Mike W.]

IMO the biggest thing is NOT to use Platinum plugs. They do not like Plats. NGK and Bosch are both good, the silvers last longer than coppers, but both perform well.

[austin8753]

you can find the Bosch W8LCR, but you have to look a little harder. if they aren't worn, i always used to media blast the tips (if full of carbon), clean thoroughly with solvent, and reinstall.

the NGK ZGR5A are a perfectly acceptable substitution, but i've had issues with the porcelain coming loose from the threaded insert - more than once. maybe those were weird, isolated situations, but i haven't used them since, unless i absolutely had to.

[garageboy]

Respectfully, the WR9LS (silver) is the plug of choice. If you search for them by model, you will see that you can even overpay for them at Home Depot! But many places sell them and they're worth it. Hope this helps.

[stuartinmn]

Respectfully, the WR9LS (silver) is the plug of choice. If you search for them by model, you will see that you can even overpay for them at Home Depot! But many places sell them and they're worth it. Hope this helps.

The Bosch W8LCR is what the Bentley manual recommends, as well as many other sources online that say either it or the NGK ZGR5A. However, to further compound the issue I've also found recommendations for a Bosch WR7DC.

I have Autolite plugs in there now, so obviously it's not like the engine will spontaneously combust if I don't have the exact recommended plug but it is kind of weird how there are so many different opinions.

[Mike W.]

Technically WR9LS, the silver plug which gives longer life supposedly. Though I had a set of NGKs I had 45K on and passed Calif smog on. And as Stewart says, the wheels aren't going to fall of if you don't use WR9LS. But lets look at the owners manual.

[turbodan]

WR9LS is spec'd for the B27. The B25 was spec'd W8LCR.

One heat range is not a significant difference in typical use, either one would work just as well.

[Aldo525]

NGK is "preferred" by BMW engines...M20 could be NGK ZGR5A

From an e30 forum, dated 2009: