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50K miles = Time for Spark Plugs!

24K views 53 replies 23 participants last post by  Sam B 
#1 ·
After getting the oil done this morning at the world famous Harix's in San Gabriel, I decided to try to change the plugs on my own. So, while I was in there, I took a few pics so the rest of you can decide if it's something you want to try.

First getting to them, a bit of a J O B. You need to remove the trunk carpet, net, and trim only to find the access panel basically glued on by double sided tape after you removed the bolts. A little tugging/prying, and it comes off.

Then, you'll notice a bracket over one of the coil packs? Yeah, because getting to them wasn't hard enough already. Luckily, the bracket comes off and goes back on very easily (I think it stabilizes/secures the intake plenum from what I could gather).

Once you get to them, process is fairly straight forward. I did them one at a time, hand tightened each, then added about an eighth to a quarter turn after that (too lazy to get a torque wrench out and check each one). While each coil pack was out, I cleaned them with an air compressor and cleaned all the contacts.

Overall, not a bad job and found the top three plugs actually harder (awkward reach) than the ones you get to from the trunk panel. Once that panel and the crazy surprise bracket came out, they were actually easier.

Oh yeah, almost forgot, changed my K&N air filter (I have two so I don't have to wait for it to dry when I scrub the heck out of it) while I was in there and checked on my Shorai which still looks brand new!
 

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#4 ·
Those plugs were 99% like new still. They say 100K for a reason. While you had fun doing it, you will see 0% improvement. Just being honest. Did my Elise after multiple years of track duty and expected a better running engine. Just didn't happen. Spark plugs are ALMOST getting to be a life of the vehicle item.

The highlight is the picture with the panel removed. Gotta put that one in the memory banks! Also 50K.. Well done, she's broken in now!
 
#6 · (Edited)
Those plugs were 99% like new still. They say 100K for a reason.
BRG, actually Lotus (Well, their service booklet that comes with the car's manual anyway...), says 54K. Hence my rationale to change them.

However, I will say, I am the guy that changes the oil every 5k, the K&N air filter every 5k (I have a spare ready to go every time), brake/clutch fluid every 20K (service booklet says 18K), transmission fluid/gear oil every 30K, and pretty much follow or exceed everything else in the service booklet. As you can see from my mileage, having owned the car for just over 2 years, I do drive it occasionally. So, I like to ensure it's always running at it's best.
 
#7 ·
Julian, they were pretty much spot on which was nice to see. I will say the bottom three (access panel plugs), were notably gunkier than the top three. And there was one (the last one under the surprise bracket), that was notably the gunkiest.

Seemed to be more of an issue of oil seeping up through the threads (not torqued properly???) as all had nice clean (slightly carbonized) firing/igniter tips.
 
#9 ·
Plack, I did a little research before buying my plugs. Most opinions were that you should stick with the factory iridium. Then the debate shifted to NGK versus Denso. At the end of the day, I went with Denso, since all I had to do was drive to my local Toyota dealership. The parts guys were cracking up when they saw my "Toyota".
 
#10 ·
Lotus says 54K?? WOW< I haven't seen a vehicle under 100K in a decade now!!
 
#11 ·
Don't make me say it BRG... RTFM! Just kidding! I was a little taken back on the service cycle as well, but who am I to argue with Lotus engineering. Also, there was no way I was going to pay Lotus upwards of $700 for this! BTW, it's not all labor. They charge like $50+ a plug!
 
#12 ·
Know the manual pretty well, was just shocked at this one. Only made it to 34K on Elise, and 12.5K on first Evora! so I never got to those service lines.
 
#14 ·
I suggest marking each old plug w/cylinder #.

If a problem arises later, you can go back and see the "history".


I carry a spare old set in the car with some tools.
 
#16 ·
Awesome right up. thanks :up:
 
#18 · (Edited)
As to hunky threads, I and really not sure of the source. You mentioned oil seeping (welting/wicking) up threads from cylinder chamber. Honestly I would be surprised of this as a source, implying lots of oil ring blow by. More likely gunk outside of engine building up, especially on the hidden rear bank, sweeping done into plug well and coating the treads as you unscrew the plugs. What leads me mostly to this conclusion is the solids on the treads of the aft bank. This stuff would not come up from within the cylinder, but rather looks like a collection of oil, dirt grease accumulated on the outside.

Good to hear no gap deterioration. As to 100k plug service, I can understand lotus cutting that basically in half. 1st they are running engine harder than Toyo service and second I normally cut service intervals in have from OEM. Goal of OEM is to get you through warranty period, including emissions period of 100k on many of the emission components, they really don't care if your engine blows up at 102000 miles they also don't care if power output is down by 20%. Whereas we as sports car owners do on all accounts.
 
#19 ·
Not that we all have dynos in our garage, but I'd love to see the REAL effect of a new set of plugs on any car for that matter. Is it significant or 1hp tops???
 
#26 ·
100k plug intervals are larely driven by legislation. My B5 Passat I had years back, serivce interval for timing belt: 90k miles. In California? 100k miles. Must be the weather.

You need nice sharp edges on the electrodes, the metal does wear over time and 50k miles is not too early at all.
 
#20 ·
@ Julian, yeah mine was just a thought/theory. Again, as seen in the pics, the plug condition was pretty good sans the gunk on the threads of the aft/bottom three.

@ Brg, not sure about the plugs, but I will say, the car was notably stronger, but it always feels fresher when I do the oil and air filter together. Perhaps the plugs added a bit too.
 
#21 ·
Love seeing a car with 50K plus miles. maybe we need to start a thread with a poll "miles on your Evora"
big +1 for driving her
 
#27 · (Edited)
Again, numbers and emissions numbers would tell the tale best. I did some online research and found little. Every thread is either some company (E3) for example, hawking their wares or some environmentalists spouting off. I'm not talking Ford Explorers circa 1998 with 200K on the odometer and original plugs here. That gets a big DUHHH! I'd love to see 50K v 100K analysis. That would actually be an interesting read!
This is like the old change your oil at 3000miles BS that lingered on unnecessarily for an extra 20yrs coutesy of the oil companies. Finally Amsoil has the balls to advertise on TV 1x/yr! Even that is questionable based solely on mileage for a garaged car in a temperate climate. I'm not afriad to tell you all that for 10yrs my old XJ was serviced with Pennzoil Syn 5W-30 every 10K or 2 yrs and the oil looked pretty damn decent when it came out as a garaged car. My Ascender gets the same protocol, it may be ~7500 miles but it is outside in Maine, but periodically gets a 375 mile run which lets the filter do its job very nicely as well as being fully heated for 5.5hrs+. That is the key. Jag was same way.
And I will tell you directly I don't give a damn if it makes a difference between a motor that last 250K v 275K. Ascender will be rusted out LONG before that. Some old bro has my Jag now probably and it will never even get serviced again....cuse the aside. Just making us question the rationale that goes back to old copper top plugs etc. Just because they look dirt doesn't mean they have any reduced performance. A 5 seconds burst of 50micron particle would make them look brand new.....yea I did this for years back in the day with snowmobiles that used to foul plugs routinely so I know how easy they cleanup. Iridium is a profoundly superior metal.

Believe me, I like to do these jobs... but is it necessary? It was a waste of time and money on my Elise after 7yrs and ~30K miles (a lot of track made me think it would be good). Noticed absolutely nothing at startup, idle or at 8500rpms!
 
#28 ·
Some sage truth in above. Last plug change I made (on PT Cruiser @102,000 miles) done for my curiosity of electrode wear, (and I must say for subsequent sale purposes) showed beautifully light brown electrodes, all equal coloration, but with a gap of approx. 3/16"!! At the time of change, car had better mileage than when younger, never a miss or hesitation, no startup problems etc. It was what I expected, based on previous experience changing my and friend's plugs after 50, 60, 70 thousand miles. This perhaps is one the good parts of computerized control of the newer engines with respect to A/F ratio, VVT and Ignition management etc on a nearly microsecond basis....(still, I miss synchronizing the SU's and Webers!.....).
Of note, removing the plug after very high mileage may pose a problem with metal galling between plug and aluminum head. Stripping threads in head can occur.
One suggestion noted to limit this possibility is to slightly tighten plug prior to removing to break adhesion/carbon/galling and then remove. When replacing, plugs I use NeverSeize very sparingly to make future removal less frightening. Another suggestion noted, is to periodically (say, every 25-30,000 miles) gently loosen/or remove/clean threads andthen replace or re-tighten plugs to limit galling possibility.
Just some thoughts..............:)
 
#29 ·
I'm looking into ordering a few densos on amazon to get free shipping. Anyone know what's the model to use/ I'm seeing different FK/SK#s...

Anyone knowledgeable enough to explain any difference in these numbers?
 
#30 ·
Factory Manual lists:

Denso FK20HR11 (Iridium) for NA

and NGK ILFR7B8 for the S

As is typical with plugs the last number is most likely the heat number, while it would be best for you to Google, as each manufacturer can be different
 
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