When do the spark plugs need changing?

Hi Bronze. I just changed mine for the first time last week. This was at 200,000 km (125000 miles) and I was amazed how good the plugs I removed looked.

Anyway it's a pretty easy DIY job, so if you want to replace them a bit early then go for it.

 

The recommended change interval is at 120K miles. However if you notice engine misfire then it would not hurt to remove and inspect (or replace) the spark plugs now. Use only the correct NGK or Denso iridium spark plugs.

You may find moisture in a spark plug well which would cause misfire. The spark igniter O-ring does not do a very good job of sealing the igniter opening.

Water can drip down from the engine compartment cowl, onto the engine valve cover. If this is happening, use black sealant on the vertical seam between the two plastic cowl cover pieces.

 

Martin, Patrick has covered it all really, but just a couple of extra checks.
Check the throttle body is clean.
I have also noticed if I move the car when the engine is cold and do not allow it to warm up "not being quick enough with the EV button or forgetting it" turning it off after moving the car a few yards, next morning I can have a a short period of rough running "missfire". The gen3 Prius seems to have real problems with this, but it is a thing I notice in the gen2 to a smaller degree when it is cold. After 6 years with my car the problem "if you can call it that" has got no worse.

John (Britprius)

 

Could it be because of the variable valve timming? H

 

I went online and searched for "scheduled maintenance for a 2014 Prius 2, and it listed 40k miles as the recommended interval for changing the spark plugs. But I see here, that people are mentioning 120k. Can anyone clarify? Thanks.

 

Toyota USA published "Warranty and Maintenance Booklet". A paper copy is included with all new cars, but if it's missing a pdf copy can be downloaded. One source is the Toyota Tech Info website, in the "manuals" tab of the home page.

The interval is 12 years or 120k miles, whichever comes first. CARB States (California and...?) are 15 years or 150k miles IIRC. Same plugs, so...

Attached is a table summary I've done of the 3rd gen US schedule, in Excel and pdf formats. A much easier read. I've attached both a 120k miles version (limit of the booklet), and one extrapolated to 240k miles.

Also attached, an excerpt from the Repair Manual, with the spark plug replacement instruction (pdf format).

Note, Toyota has revised the spec for the plug, from Denso SC20HR11, to SC16HR11, a slightly hotter plug.

Also, if you're planning to DIY, this video is very helpful. I'd take exception to their slathering up the plug threads with anti-seize and torquing to 20 ft/lb though, spec is 15 ft/lb, with no mention of lube, so presumably clean/dry threads. It's video #13, linked here.

BTW, this is a gen 2 forum, but no matter.

 

You are posting in a Gen 2 forum so YMMV.

It depends on what plugs you are using. The recommended iridium plugs (at least on a Gen 2) are 120,000 miles. Lesser quality plugs would be less. I'd expect to change regular copper core plugs every 20,000 miles.