Spark Plug Interval

[AZ Mike]

I am new to the board and have been searching/reading with great interest. I do have a question about the mileage interval for changing the spark plugs. My owner's manual for a '99 LS400 calls for changing the plugs at 90K miles. However, I have read many posts of people changing their plugs at 30K and 60K intervals. Are these shorter intervals overkill, or are there good reasons to swap out more often than called for by Lexus maintenance recommendations?

[jcrome04]

It really just depends on how the plugs are holding up. You could pull them out and see how they look.. but it's kind of a pain to get to them so I'd say while you're in there just change them lol.

A lot of people say stick with OEM or NGK. I believe Lexus recommends platinum. I went with NGK GP Platinums from sparkplugs.com

They were just over $30 shipped.

One more question.. How many miles are on your car? Do you know if they've ever been changed??

[AZ Mike]

One more question.. How many miles are on your car? Do you know if they've ever been changed??

The LS just barely passed 60K miles (I have 3 cars, so it isn't used daily), and is running on the original plugs. It runs smooth as silk; no noticeable operating issues. I just want to maintain it properly.

[Lexusfreak]

Double check the owners manual.....you might have iridium plugs in there.....not platinum's. ;)

I will be changing mine (iridium) at the 60k mile mark personally.

[erg1948]

Double check the owners manual.....you might have iridium plugs in there.....not platinum's. ;)

I will be changing mine (iridium) at the 60k mile mark personally.

I noticed a sticker underhood on my '99 saying to use iridium plugs. Is that good, or bad? Or, in other words, not as long-lasting as the platinums? This is the first I've heard of iridium plugs.

Gene

[jcrome04]

Hmm I may need to upgrade to Iridiums ;)

[Nickhere]

Double check the owners manual.....you might have iridium plugs in there.....not platinum's. ;)

I will be changing mine (iridium) at the 60k mile mark personally.

I noticed a sticker underhood on my '99 saying to use iridium plugs. Is that good, or bad? Or, in other words, not as long-lasting as the platinums? This is the first I've heard of iridium plugs.

Gene

I believe iridiums are 90k plugs vs platinum which are 60k. The iridiums have even more heat resistence and allow the use of smaller guage electrodes for "crisper" more powerful spark.

[landar]

My 98 has original plugs and at 74k miles still runs silky smooth. However, I am starting to be concerned about the

plugs "welding" into place with age. I have heard of this phenomenon, but never experienced it. Some metals will, over time,

become fused together and I have heard that sparks plugs in heads for long periods can undergo this process.

Perhaps it can only happen with dissimilar metal heads and plugs? Maybe its urban legend.... :o

[Lexusfreak]

I believe iridiums are 90k plugs vs platinum which are 60k. The iridiums have even more heat resistence and allow the use of smaller guage electrodes for "crisper" more powerful spark.

Correct.....iridiums are better, longer lasting (and more expensive) plugs than platinum's.

[lenore]

On the RX300 I pulled the plugs at 110k and they looked perfect, changed them anyway. But will tell you the iridiums are long life plugs....On the RX the change interval is 100k.... By the way stick with NGK or Denso iridium, they are great plugs..

[mejojo]

I am new to the board and have been searching/reading with great interest. I do have a question about the mileage interval for changing the spark plugs. My owner's manual for a '99 LS400 calls for changing the plugs at 90K miles. However, I have read many posts of people changing their plugs at 30K and 60K intervals. Are these shorter intervals overkill, or are there good reasons to swap out more often than called for by Lexus maintenance recommendations?

I changed my factory plugs at 200K, and only because I had to get in there anyway to do some other work.

I posted pictures of the plugs here...they looked pretty darned good.

23MPG before and 23MPG after changing the plugs, rotors, caps, wires.

Joe

Picture here:

http://us.lexusownersclub.com/forums/index...ost&id=7423

[cmmetcalf]

Double check the owners manual.....you might have iridium plugs in there.....not platinum's. ;)

I will be changing mine (iridium) at the 60k mile mark personally.

I noticed a sticker underhood on my '99 saying to use iridium plugs. Is that good, or bad? Or, in other words, not as long-lasting as the platinums? This is the first I've heard of iridium plugs.

Gene

Yes Iridiums are longer lasting in general than platinum. They can go 90K but in service in 4 LSs 400/430s I have found that a 50-60K change interval works best for me. I run 89 R+M gasoline in NC with a lot of highway milage (K+N air filter) and they make good milage and good power. After change out the cars don't stay on the starter quite as long and usually pick up a mile or so per gallon. The V8 are really smooth idlers so worn plugs just aren't noticable often.

All of the plugs I have pulled have had good color to them and fairly wide gaps with noticable electrode tip wear at 50-60K. I use NGK Iridium Laser IX plugs and install with copper based thread anti-seize so they will be easier to get out the next time. Also if you DIY be sure and don't overtighten them. Follow the instructions carefully as they come prepackaged with plug gaskets that seal the plug and cylinder head nicely against leaks. You may also want to use WD40 or some other cleaner that is safe to use of rubber to clean the plug wire end with built in transformer (later motors without two distributors '95 up I think) that goes into the spark plug well in the head---as they can build up a fair amount of deposits from the operating environment over time. I like to put them back in clean.

[GKLCPA]

I got a plug change coming up as well. Does it make sense to change the wires as well?

[Randy&Bonnie]

..

[blake918]

Yes Iridiums are longer lasting in general than platinum. They can go 90K but in service in 4 LSs 400/430s I have found that a 50-60K change interval works best for me.

I've found the same thing in my LS. I have used iridiums since I bought my LS, and 60k miles seems to be about what they last for me too. I'd probably run them longer than that, but I know it's time to change them when my mileage starts going down.

I got a plug change coming up as well. Does it make sense to change the wires as well?

Not unless they are out of spec which would be if a wire is over 25 kohms.

[Randy&Bonnie]

..

[Mike Hobbs]

At 137,244 miles, my LS400 is still using its original Denso iridium plugs. When I replaced a defective VVT solenoid valve, the tech removed several plugs for examination and measurement. All met appropriate specs and exhibited no abnormal appearance. There was no difficulty in removing or reinstalling them. I'll continue to use them until they are out of spec., otherwise become abnormal or malfunction. As for the car itself, I've owned a variety of vehicles, including the famous German makes. Elaboration is unnecessary. Suffice it to say, I hope to keep this car for the rest of my (hopefully long) life.