Speedboat

Yesterday I put some Denso IK20 plugs into my 2000 LS400. The car is running a lot better, especially because I think one of my old plugs recently died. I was smelling a bit of unburnt fuel, the engine didn't seem to have full power and wasn't as smooth.. but now the gas smell is gone now (There was never any evidence of a leak)

Now for the big news... I took her out onto the highway, and on flat ground (A/C off), I am getting 40MPG at around 75MPH. FORTY miles per gallon. Absolutely insane.. I used to get around 30, which is fantastic for a V8 barge to begin with... but I have to say that I was absolutely shocked to see 40. I did some calculations based on trip odometer and fuel gauge movement and it appears to be accurate.



During the day it averaged down to 30 or 31MPG.. this is from some city driving, A/C on, and some speeding up & slowing down in highway traffic. So, yeah, I'm not exactly getting 40MPG all the time... but in a straight line at 70-75MPH or so i was getting from 36 to 42 MPG sustained, which is fabulous!

I've never used these particular plugs before (and they aren't the OEM plugs -- those are Denso SK20R11) but they sure do seem great. I just thought I'd recommend that any of you thinking about changing your plugs should go for it!

(Note that these IK20 "Iridium Power" plugs are only rated for about 20k miles, but I only put about 5k miles a year on this car so that isn't much of a concern for me.)

PureDrifter

iTrader: (10)

lol sorry to burst your bubble, but your engine was still learning the plugs.
come back with 2 tank MPG numbers>33mpg and i'll be impressed

this is exactly the reason i change the plugs on my LS every year or year and a half with new Copper plugs.

Kansas

"Insane" is certainly an appropriate title for this thread. Carefully calculate your gas mileage for several thousand miles without paying any attention to the trip computer and then report back to us.

That the trip computer in my 2000 LS400 occasionally reports a "CURRENT" reading of 40 or 50 mpg on level ground or even 99 mpg when going downhill means nothing. It's all about the long term.

But wait! I think I see a unicorn! NO ... I see a whole herd of unicorns!

It's fun to dream.

python

iTrader: (4)

no iridium plug is only good for 20k either...they are 100,000 mile or more plugs

Speedboat

I know it sounds crazy, but it sure does seem to be accurate when I've done calculations.

Earlier today I did do a little a test. Once I got down to 3/4th of a tank, I reset the trip computer and the MPG "average" in the computer. After exactly 1/4th of a tank I had travelled 130miles, and the computer said my average over that time was 24-something MPG, which is correct. Yeah, I know it isn't 40 -- I was doing more city driving and had the A/C on for this test, but what I am saying here is that the computer is calculating things correctly. So, I'm not quite sure why it could be wrong only when I happen to be going a steady 75 vs city driving or vs going 45...?

Unfortunately, it's hard for me to 100% verify the highway MPG since I only do highway driving maybe once every 3 or 4 months.



I know exactly what you mean. When I let off the gas going 40 or 50+ I get 99MPG temporarily... but my foot was on the gas here (you can see the tach was reading about 2500RPMs in the pic) and the reading was very steady.

If I can keep it at over 30MPG highway long-term that would be amazing.. but if it does turn out I'm "only" getting 28-30 like usual, well.. I guess I can live with that!

I'd also like to add that I am running Mobil 1 0W-30 AFE. This might have a tiny bit of influence on the MPG as well.

PureDrifter

iTrader: (10)

again, +1 for copper plugs.
hotter spark
plugs are easy to change on the VVTi engines lol.

i've run 0w-40 for a long time, not a significant difference in mileage from the 5w-40 im running now.


you need to get us long term tank mileage, that's what matters.

Speedboat

Yeah I know.. unfortunately I can't really do that. As nice as this car is, it's going to be a pile of junk before I can get real long-term highway data collected, because I only do a couple hundred highway miles a year, max.

As for the plugs, yeah, they were very easy, I was surprised. It was my first time doing then, and I am glad I didn't have to worry about any wires. One of the coils was stuck in there REAL good but I eventually got it out.. most popped right out easy.

Anyway, it was just really amazing to see this so I couldn't help but start a thread about it

Speedboat

Thanks for bringing that up, it looks like I was wrong. Denso's website actually says the "Iridium Power" plugs should be replaced after 30,000 miles, not 20,000. Not quite 100k, but I am glad it's 30 and not 20... means another 2+ years for me since I don't drive it that much. Here's the FAQ: http://www.densoiridium.com/faq.php

deanbrown

Iridium is the most unreactive element known to man. It is much less reactive than platinum, and has a much higher melting point. It does last longer than platinum. The denso web site says they go 120K on their site, though I am sure they would love you to replace them 4 times as much!

Kansas

120,000 miles happens to be the recommended spark plug change interval in the 2000 LS400 maintenance manual. When I had the spark plugs in my 2000 LS400 changed for the first time during the 120,000 mile service in early 2010, I found that the factory installed spark plugs still looked like new and I could tell no difference in performance with the new spark plugs.

I created a thread about the 120,000 mile service including photos of the original factory installed spark plugs at http://us.lexusownersclub.com/forums...1&#entry401477

deanbrown

Agreed - I had 180K on my first set, and all the time I was doing them I was thinking - WTF am I doing this for they look new?

python

iTrader: (4)

yes..i sell plugs all day long..if i dont know what im talking about it reveals itself quickly

Speedboat

Well this would be a lot easier if you guys would just follow the link I posted earlier.. Just because I am new here doesn't that mean my facts are less valid.

No, I am sorry, but it does say 30k. I guess I'll have to quote it because you aren't following the link to the Denso site I posted:

"DENSO Iridium Power plugs, with their .4mm center electrode, have been developed for performance applications. Because gradual wear will “round-off” firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. For this reason, DENSO advises replacement after 30,000 miles."

These are performance plugs, with a very small electrode. These are not long-life plugs. These are not the OEM plugs.

Other Denso materials state even lower figures, such as only 15 to 20k kilometers, as seen here: http://www.globaldenso.com/en/produc...dium/qa_6.html

I understand that, but the manual recommends the SK20R11 plugs (and the NGKs). These IK20 plugs are very different from the original plugs, and so Denso states that they should be changed sooner. I would be much more inclined to follow that instead of what is stated in the manual, because the manual does not consider the fact that you could be using performance plugs.

One of my original SK20R11's failed after 79k miles (granted it was 11 years old), so it doesn't seem unreasonable to change performance plugs much sooner than that. 30k mile intervals means every 6 years for me, so that is just fine.

RA40

iTrader: (6)

Unlike past times where plug changes were 15-30K, the LS's last a long time. The NGK's came out looking pristine. I put in Bosch Platinum since I was familiar with their wear characteristics. At 100K when I yanked them with the TB service, they were again clean. For ours, I've seen no appreciable jump in MPG on plugs alone. Considering the average MPG at is ~28MPG highway, plugs alone would seem suspicious to have them upwards of 40. One of the Amazon reviews mentioned a 5% increase and that at best is 1 MPG improvement. To get upwards of 15MPG more...

I'm due for a plug change and so maybe I'll stuff these in. The GPS will tell with reasonable accuracy how well they do on the first tank. I suspect, these will have similar numbers. In which case an $8 plug will not yield significant changes over a $4 plug. Denso is taking you guys to the bank.

Remember, this is definitely a YMMV.

sethjon

I have no doubt your car NEVER got 40 MPH and am VERY doubful you ever 30. In tip top shape at optimum conditions you MAY get 28 on the highway.