Different length spark plugs

[mikey]

I just bought some new spark plugs at O'reilley, and when I removed one of the old ones, it was shorter, by about 1/4 inch. Is this OK, or should I return them to the store? They are NGK, BPR5ES-11, stock #7634. The difference is in the threads which screw into the head, not in the outer part, where the wires attach.

[mikey]

I think I'm about to answer my own question. I checked several websites, and the new longer plugs are the correct ones. I checked my receipt from the last plugs, and it lists the same part numbers, but the ones in the car DO NOT MATCH THE RECEIPT!

This might explain a lot. When I replaced the timing belt and water pump in July, I also put those plugs in. Since then the car has backfired through the muffler on desceleration a bit, and the mileage was awful, dropping from near 30 to under 25, perhaps worse. I've been going crazy checking everthing I could think of, but no luck.

What spooks me was that the clerk scanned the box the plugs came in, and it came up correct, but the plugs in the box were wrong. I'm not sure about the individual boxes inside of the 4 pack box. I should have looked at the plugs closer, but I had more on my mind.

Incidentally, the wrong plugs were marked NGK B6HS. Has anyone out there had a similar experience? Could the wrong plugs cause damage, and is such a drop in MPG to be expected?

I just took a little test drive, and all seems better. The next tank of gas will tell a lot.

[ARCHINSTL]

See what those B6HS #7534 plugs DO fit - very few Japanese cars - and none are ours. Amazingly, they fit the second car I ever owned - a 1952 Morris Minor sidevalve (aka flathead/L-head) 4.
http://www.ngk.com/results_fitment.asp?pid=b6hs
Here is the contact page for NGK: http://www.ngksparkplugs.com/About_nGK/contactus.asp
Send them a note - worth a try - maybe you can get a coupon - or baseball cap. Obviously a packaging error.
Tom M.

[dlb]

i didn't have an experience like this with spark plugs but i did with a clutch. it sucked--my dad and i were rebuilding the engine for my '82 air-cooled VW westfalia and i got a new clutch since we had the engine out. went to put it on but it didn't fit at all! compared it with the old one and it was totally different. took it back to the parts place and after sleuthing for 10 minutes they finally figured out that it was packaged incorrectly. they could get me the right one but not for several days due to a holiday weekend, and we had to have the engine back in so we could leave for our vacation before then, so we put the old clutch back on. works fine but i was still choked. just goes to show that mistakes can happen at any point in the chain between manufacturer and consumer.

[Petros]

parts number mix ups from the packaging plant are not uncommon unfortunately. I bought a package of Beck-Arnly rings and got three different size rings in the same box! Needless to say I insisted on a different brand when I returned them. I have even gotten the wrong DVD in a movie box. It always pays to double check the old against the new before you install it, especially if it is something difficult to get to like a clutch. I am in the habit of doing it on everything now.

Those longer spark plugs likely where a high temp plug, that would cause preignistion and misfires. You always want to run the coolest range spark plug that will not foul. Likely the Morris minor is more prone to fouling so they need a higher temp plug than the Tercel.

I am surprised NGK would be so sloppy with packaging, they are a very reputable company and the only plugs I will run, I find them more durable than Bosch, Champion, Autolite, etc.

I would definitely write the company and let them know that you risk engine damage because of the packaging mistake. They may not do anything about it, they would want the batch number (unless by now they already know about it). They might send you a coupon, or ignore you.

[mikey]

A follow up........The mileage is back to normal, 28-30 mpg. The wrong plugs were shorter than normal, so the park was occurring either flush with the cylinder wall or slightly behind it, causing the fuel to not completely burn. Amazing what 1/4 inch can do to proper combustion!

Thanks

[Petros]

I am not sure the location of the spark will make that much of a difference, more likely I suspect you were getting misfires at speed (hardly noticeable) from the wrong heat range of spark plug. Running the plug too hot or too cold will cause misfires, but only at high speeds unless it is really carbon fowled.

[mikey]

Makes sense to me, in my limited knowledge of mechanics. The car idled fine with the wrong plugs. The plugs were in too short a time to get fouled, I suppose, and they looked clean when they were removed. I got the location of the spark idea from another website, but not from anyone with any authority.

[Petros]

FYI, the wrong heat range plugs can get fouled in 5 to 10 min. at fwy speeds. Each spark plug would have 3750 or more times in ten min. You are thinking of plug fouling in a properly running car would take many 1000s of miles. Not true if it is not running properly. Too cold a plug gets carbon deposits on the electrodes that will allow the spark to ground, too hot a plug will heat up the electrode and start to melt the electrode tip, raising resistance. You always want to run the coolest plug possible to make the tip last the longest, but too cool will cause carbon build-up and fouling.