2009 Toyota highlander, 115K miles, runs great! I am unsure if I should get the coils and spark plugs replaced for preventative maintenance? There have been no misfires, codes, or signs to get them changed, and I'm kinda leaning towards "if it ain't broke don't fix it", but I wanted to get some opinions on this service. They have never been changed before. Also, since it's a 6-cylinder so the back 3 plugs are hard to get to and I'm not that skilled, so it will have to go to the shop for this service. Should I wait for more mileage, wait until there is a problem, or just get it done? Thanks!
What does the owner’s manual say?
Generally, the iridium plugs are good for 120K or so. Even with the six cylinder, the first three should be easily available (in terms of removal). It wouldn't hurt (as long as you are careful, and extract the plugs when cold) to take a look at the three plugs that are more easily accessible. There are plenty of YouTube explanations of what a good plug looks like, and what bad plugs look like.
I'd leave the coils alone. However, changing the plugs correctly should extend the life of the coil packs.
Given the age and the mileage, if the valve cover gasket has never been changed in twelve years, you might want to do that, as part of preventive maintenance. That would prevent oil from contaminating the spark plugs, in the future.
If it were me, and these items hadn't been done before, I'd do them now, as preventive maintenance, along with an inspection of some other items, such as the radiator. (If it's the original radiator, it's near the end of its life). You might also want to do a "drain and fill" on the transmission and check on the state of the gear oil in the differential.
Generally, the purpose of maintenance is to spend a bit, upfront, rather than spending more later, because you allowed the vehicle to "run to fail." "Run to fail" is best left to for a vehicle where there's a flaw that would be too expensive to fix (such as an old car with a balky transmission). Your Highlander seems like it's very much worth doing reasonable preventive maintenance.
Thanks! makes sense
The iridium park plugs can last 100-120k miles, but I would not change them unless you see some signs of change in performance on the car, simply because for changing the rear ones, you have to take off the intake manifold which is a costly/time consuming job.
I just replaced the plugs on my 2012 BMW X-3 325i SAV [86000 Mi.] NGK's were recommended as were Bosch; but after reading the information on Spark Plugs. I chose to use Double Platinum from Auto lite. [on my previous 2005 BMW X-3 I actually installed Pulstar Plugs {improved performance and MPG a little}.
The problem with waiting for performance change in the car, for changing the plugs, is that you're likely going to shorten the life of the coil packs, since they have to work extra hard to make up for the degrading quality of spark. Then, your changing coil packs and plugs, rather than just plugs.
