I am trying to decide whether to change the spark plugs on my 2003 Lexus GS-430. I am the original owner -- the car was manufactured in April 2003, and I drove it off the dealer's lot in July, 2003. Although I have only 57,000 miles, here are the reasons I am considering changing them:

1) My fuel economy has dropped by about 3 mpg in the past few months. However, this could be due to a change in driving patterns more than anything else - I am driving shorter trips than I was before. I am up to date on other maintenance, such as changing the air filter, oil, etc.

2) I am concerned about ease of removing the old plugs...I have heard if you keep them in until over 100,000 miles, the threads on the plugs can "fuse" to the threads on the head, which of course is problematic. Of course, I could just remove and re-install the same plugs to avoid this problem, but if I am going to do that, I might as well put in new plugs.

Also, has anyone changed their plugs on the 2001-2004 GS-430? Are all of the plugs easy to get to? The one on the driver's side closest to the driver looks like it might be a bit hard, with the brake cylinder a bit close...

 

Iridium plugs arent scheduled to be replaced until 100k miles. A lot of people replace them at 60k as a part of their 60k service. In my 6 years as a lexus tech, i have yet to see a plug sieze in a spark plug hole. I would say that if you want to wait, you will be safe to wait. If you dont mind spending the money to fork out 8-10 bucks a plug, then i would go ahead and do them. Personally, i replace my plugs every 60k, but thats me. Replacing them is not that difficult at all. Once you get the engine cover off, and unplug all the coils, its pretty simple. A 10mm bolt on each coil pack, and each one slides out. Then a short extention and a spark plug socket, or if you have the long plug socket you can use that too, and the plugs come out easily. If you are mechanically inclined at all, i would say that you shouldnt have any problems with replacing the plugs, and you should have them done in under an hour. Good luck

 

RTGS400,

Many thanks for the response, particularly about not having seen or encountered seized plugs in the Lexus V8 - This is very reassuring. I have changed many plugs on engines earlier in my lifetime, but never have changed a set on an engine so expensive. Nor have I ever changed a set of those 100,000+ mile plugs -- I always seem to trade cars before I encounter that milestone. But the GS430 I have is a keeper, and I expect to have it for some time, and want to maintain it in peak condition. I went back and checked -- The manual says to change them at the 120,000 mile mark. But I do not mind the expense of new plugs -- Probably less than $100 or so, for the chance that I might eek out a bit better performance. I plan to perform a bumch of other preventative maintainance next month, so I plan to go ahead with the plug change then.

Any recommendations on what I should use as an anti-seize compound when installing the new plugs? This is another aspect of changing plugs these days that I haven't dealt with before....

 

Just a dab of standard anti-seize on the threads will work for you. I know plenty of people who dont use any, and they dont have any problems, but since you're putting a steel thread into an aluminum head, i would use just a dab. Plus will run you about 8 bucks each, depending on where you get them. Stick to the OEM Iridiums, and you'll be good Good luck with the maintenence, im sure you'll be fine! Enjoy that GS well past 100k miles, because im at 170k on my GS, and i love it!

 

...replacing them early is SO much better than waiting.

when I purchased my LS form the prev. owner he gave me all the paperwork, receipts, etc for all the work that had been done to the car, both by him and the first owners. He said he'd replaced the fuel pump, timing belt, spark plugs, etc...he had the receipts to back it up.

Well I'll be tearing into my car to make sure soon, because the plugs and wires I pulled out were the factory originals from 1994, over 150K miles ago. Apparently, this car LOOKED like it was being taken care of, and that's it. That said, you do intend on doing this yourself, right? If not, ask to see the old plugs; no mechanic should have a problem with that.

 

As far as the gas mileage drop - did you check to see if you have an O2 sensor code? They should not go bad at that mileage but who knows?

Be happy you don't have a newer Suburu 6 cylinder. I hear you have to raise the engine to get at 2 of the plugs.