Why New Plugs at Only 8,000 Miles?

Hey guys,

Why is it YAMAHA recommends plugs be changed at only 8,000 miles??

I could see if this was a track bike and you ran the piss out of it, but it's not.

Cars can go 100,000 miles on plugs, why not say 30,000 with the FJR??

I had mine changed at a dealer (I was there getting other stuff done) at about 10,000 miles and the tech showed me the "old" plugs, they looked almost brand new with a "slight" tan color on the plug.

Do you guys really change your plugs around 8,000 miles??

Engineers looked at a worse case scenario to prevent anyone in any situation from having a plug issues. As far as why they don't last as long as cars, a lot of motorcycles fire their plugs in a different way than cars; the spark plugs get fired even when the combustion isn't on that cylinder, combined with high rpms.

Having said that, plugs on my bike weren't changed at all by the previous owner until I did at 22k, and I did it for a second time at 44k miles. Stock plugs each time. No difference in performance before or after either change.

carlson_mn said:

plugs on my bike weren't changed at all by the previous owner until I did at 22k, and I did it for a second time at 44k miles. Stock plugs each time. No difference in performance before or after either change.

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That's what I figured, I'm going to do them about every 20,000 miles, unless I experience rough running before then.

Can cars go 100k? Or is it simple marketing and an ECU that adapts to a decreasingly-effective plug while slowing delivering decreased performance. I'm of the opinion that extended servicing intervals is a marketing ploy genned up to try and offset the increased purchase prices.

The ECU can compensate so you have a plug that "looks good" when you try to read it. After all, the ECU has been "adapting". But what has it cost to the ideal performance while adapting to a worn plug?

Bounce said:

Can cars go 100k? Or is it simple marketing and an ECU that adapts to a decreasingly-effective plug while slowing delivering decreased performance. I'm of the opinion that extended servicing intervals is a marketing ploy genned up to try and offset the increased purchase prices.
The ECU can compensate so you have a plug that "looks good" when you try to read it. After all, the ECU has been "adapting". But what has it cost to the ideal performance while adapting to a worn plug?

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I agree some of the extended service intervals might be marketing but some are also better technology.

But does a plug really get that bad in only 8,000 miles that the ECU has to compensate? That would be my question.

I'm just looking for a "happy medium".

I think the 8,000 mile change is much too soon and according to how my "old" plugs looked, it was, BUT, I wouldn't leave them in for say 50,000 miles either.

I'm betting about 20,000 miles is fine.

How long is everyone else leaving the plugs in for???

I will bet it is something like valve check intervals also, can you spell EPA.

Bounce said:

Can cars go 100k? Or is it simple marketing and an ECU that adapts to a decreasingly-effective plug while slowing delivering decreased performance. I'm of the opinion that extended servicing intervals is a marketing ploy genned up to try and offset the increased purchase prices.
The ECU can compensate so you have a plug that "looks good" when you try to read it. After all, the ECU has been "adapting". But what has it cost to the ideal performance while adapting to a worn plug?

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What can the ECU do to compensate for a bad plug?

Bounce said:

Can cars go 100k? Or is it simple marketing and an ECU that adapts to a decreasingly-effective plug while slowing delivering decreased performance. I'm of the opinion that extended servicing intervals is a marketing ploy genned up to try and offset the increased purchase prices.
The ECU can compensate so you have a plug that "looks good" when you try to read it. After all, the ECU has been "adapting". But what has it cost to the ideal performance while adapting to a worn plug?

Click to expand...

The left rear (#1 cyl) on my Windstar went 110 000 miles, and just before I finally changed it the engine was running within spec on all six.

The plug that came out had a gap you could have ridden an FJR through, and I know it was original because the plug identifier is unique to the factory.

110k on my 2006 cts-v with original plugs, car ran better than stock 1/4 mile times @ 103k miles and mpg is right where it should be. Been meaning to change them soon but they seem to last. Stock AC Delco plugs. 100k is the standard on cars for the last decade.

60,000 miles and I don't know for sure if the plugs have ever been changed. I think they were, but who knows?

Worry less, ride more.

carlson_mn said:

110k on my 2006 cts-v with original plugs, car ran better than stock 1/4 mile times @ 103k miles and mpg is right where it should be. Been meaning to change them soon but they seem to last. Stock AC Delco plugs. 100k is the standard on cars for the last decade.

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What I don't like about leaving them in for 100,000 miles is that they can be a bitch to get out.

Had a mechanic tell me years ago to take them out at 50,000 and put a little something on the threads so they're easier to get out at 100,000 or so,

SoCalFJR1300 said:

carlson_mn said:

110k on my 2006 cts-v with original plugs, car ran better than stock 1/4 mile times @ 103k miles and mpg is right where it should be. Been meaning to change them soon but they seem to last. Stock AC Delco plugs. 100k is the standard on cars for the last decade.

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What I don't like about leaving them in for 100,000 miles is that they can be a bitch to get out.

Had a mechanic tell me years ago to take them out at 50,000 and put a little something on the threads so they're easier to get out at 100,000 or so,

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NGK does NOT recommend using any sort of anti-seize on plug threads. I had always used it but not for the last several years.

https://www.ngksparkplugs.com/pdf/TB-0630111antisieze.pdf

I agree that the interval is a bit on the short side. Mine came out looking really good. Given the cost of approx $34 to change them, I will be doing them slightly beyond their recommended interval (better be safe than sorry I guess - something like every 20000 km (or 12000 miles for most of you)).

I've got 22,000 miles on my '13 model. I hadn't even considered a plug change yet.

It's still running fine and getting mileage in the mid-40s.

Hmmm.....

And the GEN III's don't fire the plugs the same way as the older ones. Each plug has its own coil. My Prius is like that and has 65,000 miles on the original plugs. Still runs the same as always.

SoCalFJR1300 said:

Hey guys,

Do you guys really change your plugs around 8,000 miles??

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No.

JamesW said:

I will bet it is something like valve check intervals also, can you spell EPA.

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I do not think either situation is being driven by the EPA. In the case of the valve check intervals, I believe that is actually a reasonable number of miles between checks. It was chosen based on the degree of confidence that the valves would remain in runnable state until the next check if they are checked and are found to be at the lower edge of the spec range.

In the case of the plugs, I don't have a clue why they chose such a short interval, but 8k miles would have to be about 1/10th of the P95 MTBF for that application. That seems an overly cautious replacement interval. And furthermore, they want you to actually check the condition of the plugs every 4k miles?

Denver_FJR said:

Bounce said:

Can cars go 100k? Or is it simple marketing and an ECU that adapts to a decreasingly-effective plug while slowing delivering decreased performance. I'm of the opinion that extended servicing intervals is a marketing ploy genned up to try and offset the increased purchase prices.
The ECU can compensate so you have a plug that "looks good" when you try to read it. After all, the ECU has been "adapting". But what has it cost to the ideal performance while adapting to a worn plug?

Click to expand...

What can the ECU do to compensate for a bad plug?

Click to expand...

Nothing. Not even a more advanced automotive ECU can compensate for worn plugs.

I would guess that in a car (or the new 3rd gen FJR with COP) the spark voltage is considerably higher than on the shared coil design of the 1st and 2nd gen FJR. What that means is the spark will be able to jump a larger gap with no problems. Larger gap = larger spark = better fuel ignition source. So technically, your bike should run better with worn plugs up to the point where the coil no longer provides adequate voltage to reliably arc the gap.

As for real world replacement intervals... I pull the plugs out every 25k miles (26k miles recco per the manual) for doing a valve check to make it easier to turn the engine by hand. That is a very convenient time to swap in new ones since they are out already. Even the standard non-iridium spark plugs have no problem lasting 25k miles.

On a 3rd gen? There do not seem to be any iridium plugs available that are an exact matches for the new design's longer center electrode tip. So since you are using "conventional" resistor plugs I'd just stick with the 25k miles. If they ever do come out with an exactly matching iridium, you should be able to go 50k miles easily, but you'll still have to unscrew them every 25k miles for the valve check.

I've always changed them with the valve adjustment (i.e. 26200 miles) and never had a problem.

The Subaru, on the other hand, recommends 50k between changes, and it starts to degrade at about 40k, and it takes four freakin hours and seven skinned knuckles and lots of swearing and a sore back to change them out. But I'd rather do that than pay the dealer $400 to do it.

I suspect that modern cars ability to adjust spark with ECU, better fuel atomization and metering according to conditions, and better ring/cylinder tolerance contributes to longer plug life.

I also suspect that motorcycles running at higher RPM's (i.e. plugs firing more), simpler ECU's (i.e. worse fuel metering) and our penchants for wringing the snot out of our engines contributes to shorter plug life.

Thanks Fred. That was my plan; just put new ones back in when checking the valves.

Modern plugs in cars can go 100k plus miles because of advances in the plugs themselves. Modern plugs have platinum and/or iridum tips, that while they dont conduct electricity as well as old school copper plugs, they are much more resistant to wear, therefore they last longer.