'05 Scion tC, bought used. 145k miles , unknown if spark plugs were ever changed. Should I change 'em?

Question

No funky smoke colors, no issues, runs like a champ. Just don't know if it was ever done before or not.

Bought at 92k, car is now at 145k miles

Leave well enough alone or change 'em?

Answer 1

Definitely change them. Even if you pull them out and they looks okay, I'd still change them. Yes, it might cost you a few dollars (denaro, yen, rubles, whatever) to do so, but knowing the state of the maintenance you've done to the vehicle will give you peace of mind as well as help the vehicle to run as well as it can. Any maintenance you deem worthy of this should get your attention. These are things like antifreeze and brake fluid, too.

It seems nobody (even myself ... dang, called it out, didn't I) changes these very necessary maintenance items. Brake fluid should be changed every two years. Antifreeze every 5 years (or at least check the schedule on it from Toyota). Seriously, if you are at all worried about the plugs, since the vehicle is at 145k (whether km or miles) change them out and know that you have good plugs in there which will last you another 100k without issue. Any other maintenance item which you feel uneasy about should be done as well. (After reading a few forums, I guess your tC has a chain and not a timing belt, so you can probably leave that alone. :o)

The big difference in all of this is that if you get it done (or do it yourself), you know where the vehicle lies instead of having a lack of knowledge. I can tell you from experience, most people want to do right by their vehicles, but don't. Don't trust in what other say they've done, do what you believe you need to do, especially if you like the car and want to keep it for a while. You can never do too much maintenance ... well, you pocket book might tell you otherwise. Do what you feel is right, but changing out the spark plugs might give you that tweak in gas mileage you thought you should have, but don't. In the end, you won't hate yourself for changing them out, plus you'll have the added knowledge your car is taken care of until the next time it needs plugs.

Answer 2

The only real way to answer this question is to pull the spark plugs and check their condition. If the electrodes are starting to look worn then replace them, if they still have useful life then check the gaps are still good and save yourself a bit of money by using them longer.