Spark Plug pictures after 120,631 miles

Still looks good to me. In fact I would wire brush them and put them back. I'm all about saving money!

 

The used plugs look pretty good. However the answer to your question would be based upon the spark plug gap.

The correct gap is 1.0 to 1.1 mm. If the gap is 1.2 mm or more, the plugs should be replaced. Do not adjust the gap of a used iridium spark plug.

 

nice pics! how much are 4 plugs?

 

Why is that?

 

Yeah those plugs are in amazingly good condition given the number of miles. I recently changed mine for the first time at 200,000 km (124000 miles) and they looked very similar to yours. Very little wear.

 

There is so little wear on those plugs its unbelievable. I personally believe you could clean them up and be good for another 50-100k miles but others have disputed me on that.

The old ones are made in Japan so they're likely better lol.

 

My belief is that the ground electrode of a used spark plug will become brittle over time, as it is exposed to repeated heat/cool cycles. A plug that has logged 120K miles may have experienced 3,000 or more heat/cool cycles - if you drive 40 miles per trip. Following is text from the Toyota repair manual:

1. INSPECT SPARK PLUG
NOTICE:

Do not clean the spark plug with a wire brush.


Do not adjust the gap of the used spark plug.

(a) Clean the spark plug.

(1) Using a spark plug cleaner, clean the spark plug.

Air Pressure Duration
588 kPa (6.0 kgf/cm2, 85 psi) 20 second or shorter

HINT:


If the electrode is wet, dry it first, then clean it with a spark
plug cleaner.


If the spark plug is wet with oil, remove the oil with gasoline
before using a spark plug cleaner.

(b) Check the appearance.

(1) Check that the threads or insulator of the spark plug

are not damaged.


Recommended spark plug:

Supplier Type

DENSO SK16R11

NGK IFR5A11

(c) Inspect the gap.

(1) Using a spark plug gap gauge, measure the gap of
the spark plug.

Standard: 1.0 to 1.1 mm (0.039 to 0.043 in.)
Maximum: 1.2 mm (0.047 in.)

If the gap is greater than maximum, replace the spark plug.

 

i guess there are two ways to think about it: if you put the plugs back in, you have to inspect them again when? if you replace them, you're good for another 120k.

 

Yeah, I'd toothbrush them with carb cleaner. Actually quite effective. Some plugs don't take kindly to wire brushing, or sand blast, and I think the long-life plugs are in this category.

Still, after digging down to those, and with new spark plugs on hand, c'mon...

 

I suspect the gap is too large.

 

I'm sure it could go a bit longer. But, when the weakened ground electrode (as clearly visible in the image) or porcelain isolator breaks off, the engine will go kaput. Why risk it? Spark plugs are cheap.

 

Here's a zoomed in view of OPs last photo. The green line is cut and pasted, so the same length on each plug. The gap of the old plug still looks fine.



Also, there's still loads of wear remaining on that ground electrode. I suspect that these plugs could run another 120,000 miles and have nothing fall apart. Still I agree with Jacek though, with the relatively low cost of a new set of plugs there's no point in risking it.

 

I don't think it is asking too much to spend $40 on four iridium spark plugs every 120K miles. The idea is to replace the plugs before the engine starts to experience misfiring, after all. And, note that the engine ECU will log a misfire DTC only when a plug has a 25% misfire rate or greater.

In the not so distant past, it was customary to replace regular spark plugs at 12K mile intervals, and later, platinum plugs at 30K or 60K mile intervals...

 

And in the past, I used this spark plug cleaner/tester quite often. You hook up compressed air and plugged into 110v.
You first clean the plug with the compressed air/sand mix. Then move the plug from cleaning chamber into the screw-in test chamber, push on a plug wire, push test to produce a spark, watch the arcing of the spark on the electrodes via a mirror, and increase the air pressure (as would happen in the combustion cylinder) until the plug starts to misfire. Some plugs misfired at an unacceptable low pressure level.

 

Use of such a cleaner is still acceptable per the Toyota repair manual, see my post #9 above which shows the air compressor pressure spec of 85 psi, 20 seconds run time.

 

I'd agree with that logic. If you are at the point where you've already purchased replacement and removed the old plugs, then I think your "all in" for replacement.

I know many Prius owners are about conservation and getting the most out of a resource, but even if the old spark plugs looked great, which they do, I'd be hard pressed to re-install plugs with 120,000+ miles on them. I'd put the brand new plugs in with 0 miles on them, and consider it a preemptive action, avoiding future deterioration.

 

Well, the question is whether the 120K mile or 150K mile change interval is correct from an engineering perspective. According to the Denso website, their long-life original equipment iridium spark plugs have a 120K mile service life. See the second paragraph of following citation:

How Long Do Iridium Plugs Last?


The California PZEV requirement is based upon legislation. As you know, there is no difference in the iridium spark plugs installed in cars shipped to California and CARB states, vs. non-CARB states.

I think it is likely that Toyota accepted the requirement and figured that some % of those cars will log misfires from 120K miles to 150K miles, and Toyota will accept the associated warranty expense.

Suppose 30% of the shipments are to CARB states and 10% of those cars will actually log more than 120K miles during the warranty time duration. Say 30% of those cars log misfires sufficient to set a DTC. That is a pretty small percentage overall: less than 1% of total US shipments.

However, as an owner interested in performing timely preventive maintenance, I think it is very appropriate to change the plugs at 120K miles. So by not making the plugs last until 150K miles, you lost $10 in savings...