Installed New Spark Plugs at 138,000 miles

Liquid wrench, my friend. Or PB blaster. Or pick-your-favorite-penetrating-oil.

Be careful with "lots of force" on any engine part. It's an easy way to turn a routine job into a nightmare.

 

One of my tech friends would break the plugs loose with a long ratchet, then finish the removal process with his impact driver (not gun). I am not brave enough to try it, though.


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And use anti-sieze compound on the new plugs.

JeffD

 

Although this is a controversial topic, anti-seize can cause misfire issues if applied incorrectly and also requires the user to reduce the final tightening torque. NGK advises against using anti-seize since their spark plug threads are already coated with a substance that prevents seizing. I usually install my spark plugs dry, torqued to the spec provided by the spark plug mfg (usually 18 ft-lbs).


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^ I'm not sure about this, but appreciate the heads-up. I've always used a little anti-sieze, but will keep your caution in mind, read up on it when the time comes.

 

Both NGK and Denso have provided original equipment iridium spark plugs for the Prius.

Note that the Toyota repair manual spec is 13 ft.-lb.

 

Thanks for posting the pictures jgod.

That's not really so much "terrible shape" as you may have thought. Sure the arm has a fair amount of deposits after being in there for 138000 miles, but there is very little wear and the gap and the business ends of the electrodes look quite good.

 

http://www.ngksparkplugs.com/pdf/tb-0630111antisieze.pdf

NGK's spec is 18 ft-lbs for our plugs:

NGK Spark Plugs USA

I would follow 18 ft-lbs vs 13. 13 is pretty low - and that spec makes me nervous considering the recent issues with Honda plugs that have ejected themselves from the cyl head when torqued to that spec.

 

One issue with either of the above torque values is that they're so low, with a typical 1/2" drive torque wrench it's down at the bottom of it's range. I've heard that's where they tend to be off by the widest margin.

My torque wrench is of that variety, maybe I'll pick up an extra 3/8" drive inch/pound wrench, research it a bit.

Off-topic, was at the dentist yesterday, getting (expensive!) tooth maintenance: he was using a super-tiny torque wrench on this implant I'm getting, LOL.

 

Your choice. However:

1) the Prius is not a Honda.

2) I have noticed some posters complaining that they notice unusual drag on the plugs as they try to remove them, which shows that insufficient torque upon installation is not an issue. I also have noticed this. The longer the plugs remain installed, the harder it will be to remove them - hence I feel that is a good reason to change the spark plugs no later than at the recommended service interval of 120K miles. Not to mention the spark plug gap growing over the plug's service life, regardless of how good the tip might look in a photo. The spec is 1.0 to 1.1 mm and it is not advised to adjust the gap on a used plug as the ground electrode may weaken and fall off.

3) I haven't noticed anyone saying, "...gee, these plugs came out so easy, I am surprised they didn't eject on their own."

Yes, that would be the proper tool. 156 in-lb would be 13 ft.-lb.

 

1) Fair enough, but the spark plug mfg is specifying this torque value, not me. Besides, for spark plugs, a few ft-lb more is not going to make a huge difference...especially when you consider the number of people out there who are tightening by feel.

2) This can vary. I did one G35 with 120k one month and the plugs were almost finger tight. I did my neighbor's G35 about two months later, which only had 90k, and I was wrestling with the plugs. Regardless, 120k does not seem to be a problem.

3) I use this torque wrench and find it to be an excellent tool for the money. CDI manufacturers Snap-on's torque wrenches (but to different standards, obviously): CDI 2502MRMH Micrometer Torque Wrench

 

A lot of valid points made by many people.
1) Tighten to Toyota's specs (13 ft-lb) as Patrick noted may be best. Toyota told 1,000s of part manufactures to make a part to meet certain requirements, which Toyota then assembles into a car (in our case, a Prius).
2) NGK's higher value of 18 ft-lbs (as noted by The Critic) is what NGK says the spark plug can handle, but shouldn't deference go to the engine manufacture, Toyota and their 13 ft-lb specification? Perhaps the additional 5 ft-lbs over Toyota's recommendation may become a problem down the road?
3) The Critic's reference to many people tightening by hand is probably the biggest culprit, whic probably lead to NGK's Techinical Service Bulletin saying NO anti-seize lube.
4) I personally think a very, very, very light coat of anti-seize lube, say the width of your pinky and thinly applied to only one side of the spark plug should be sufficient. This thin coating will work its way around all the threads as the plug is scewered into the cylinder head and tightened to 13ft-lb with a torque wrench.

 

Did you see any improvement in MPG after replacing the 138k plugs?

 

And that's right where you should stop.

When a manufacturer writes a spec for an application, that spec should be followed. In the case of spark plugs, the torque is specified to prevent damage to the plug, not to the valve cover... the bolts holding the cover on are torqued much higher than the plugs!

Putting grease on threads that should be dry is not a good idea. For one, the torque specified by the manufacturer is most likely a "dry torque": what is achieved from dry thread-to-thread friction. Greasing the threads means that a lot more thread-to-thread friction will need to be generated to achieve the same torque... this can end up damaging the threads if one is not careful.

For two, careless application of grease can end up to misfires should the grease work its way to the head of the spark plug.

Just don't go thinking you're smarter than THE COMPANY THAT MANUFACTURES THE PLUGS and make up your own installation procedure. It's spelled out to you for a reason.

 

No, no, no....get the Harbor Freight 1/4 torque for $14. I just bought one and am now:

1) Looking for something to use it on.

2) Am afraid to use it.....

So, if someone does use it on their plugs and posts their experience...

 

Sounds like a good deal.

Then why not post a picture of it over your other thread . Torque Question? Help an old altar girl? | PriusChat

 

I do not think it will be easy to obtain a spark plug socket that can fit a 1/4" wrench. The 1/4" torque wrench would be suitable for small sockets like 10 mm and smaller.