Spark Plug Inspection

Well, I'll tell you some basics from years of wrenching: invest in a couple of tools first. Shop vac, torque wrench, and a jar of anti-seize. All 3 of these things will last you for years to come.

A well-seasoned Ducati wrench told me this as he mentored me in Ducati valve adjustments/tune-ups; using a torque wrench will put you light years ahead of problems and other wrenchers.

After you pull the spark plug cap use the shop-vac to vacuum around the plug area. On older/higher mileage cars I've used whatever it takes to piggy back that vacuum hose down into the hole; 2 feet of fuel line hosing, whatever, you just gotta clean out the plug area. Using an air-compressor only pushes foreign materials deeper into the affected area.

Anti-seize; "a little dab'll do ya" goes a long way here. Just apply on the top half of the threads. "Top" being as how it will be positioned in the engine. Using less anti-seize also has less effect on your torque wrench when re-installing the plugs. Yes, find the torque values for the spark plugs BEFORE you buy your torque wrench-this will help in buying the correct tool. Newt-meters, foot-pounds, etc..
Seem like overkill? Yes, it is. However, consider that you are playing with one of the 3 essential operations of any combustion vehicle which is mandatory for 100% efficiency-spark, gas, air. But, it's like any other new stuff you do; with repetitions it gets easier and faster.

 

It is sufficient to remove the relay box. Yes, you need to remove the wiring harness connector from each igniter before you can remove the igniter, since the wire harness length is pretty short. Find the little lever on the connector which serves to lock the connector in place, and press it as needed to unlock.

As previously suggested, a vacuum cleaner will help you to remove whatever debris exists. Use a mirror to help you to look into the spark plug wells.

Use a very small amount of antiseize lube on the spark plug threads when reinstalling the plugs. Be very careful not to cross-thread the plug when installing in aluminum heads. I use a length of black rubber hose as a "wrench" to lower the plug into the hole and get it started. The tail of the plug fits into one end of the hose. The idea is that the hose will slip off the plug, if the plug is starting to cross thread.

Tightening torque is 13 ft.-lb and you need a 16 mm (or 5/8") spark plug wrench socket.

 

Why are you pulling spark plugs on a 2009 Prius? You can't possibly have 100,000 miles on the car yet, and the Denso Iridium tipped plugs generally last that long or longer.

Remember the old adage "if it ain't broke, don't fix it"!

 

• Check gap 1 ~ 1.1 mm

If you have Iridiums in there, be very very careful when working at the plug tip.
They are not designed to be altered, and are manufactured to last the requisite number of miles (or thereabouts).
It is oh so easy to snap the tips off of Iridiums, so if you do get them out, clean them very carefully, check the gap very very carefully (if it was me, I'd just clean them), and reinstall.
Bear in mind that the crush washer on the plugs will be crushed from the initial installation, and reseating them may be an issue.

 

Yes, the gap on used iridium spark plugs can be checked but not adjusted.

 

2009 - don't bother you will do more harm than good.

Also, contrary to many old school mechanics - antiseize is not recommended on sparkplugs:

http://www.ngkplugpro.ca/content/contentfiles/pdf/NGKSP-0907-1R-Anti-SeizeonSparkPlugs.pdf

Also, you are better off tightening the spark plug as recommended by the manufacturer than using a torque wrench. For example some plugs say 5/8 turn past hand tight. If you lube the threads with antiseize or anything else the thread tension will be significantly higher at a given torque.

From Champion:

Here are a couple of tips to help assure the success of changing spark plugs. The first is to remove spark plugs from aluminum cylinder heads only when the engine is cool. Since aluminum and steel expand and contract at different rates, removing spark plugs from an aluminum cylinder head while hot can actually cause thread and cylinder head damage. Before installing the spark plugs, make sure the threads are clean and in good condition. If in doubt, run a thread chaser through the plug opening in the cylinder head. Champion recommends that you do not use an anti-seize compound, since one has already been applied to the plugs at the factory. Next, install the spark plugs finger tight and, if using a taper seat spark plug, use a ratchet to rotate 1/16 of a turn. If using a gasket seat type spark plug, after installing finger tight, turn 1/4 to 5/8 of a turn. If this procedure is followed, spark plugs will not back out nor will they seize in the cylinder head.

http://dodgeram.info/Engine-Gas/SparkPlugs/spkplghnbook.html

 

Yes, CCW to loosen. I would not apply grease to the seals as that might cause the rubber to deteriorate.

If this concerns you, perhaps it might be reasonable to use a thin bead of black urethane sealant to glue the bottom of the four gaskets to the valve cover. In that case when you remove an igniter, the gasket will remain attached to the cover.

 

The original equipment plug is either Denso SK16R11 or NGK IFR5A11. The plugs that I have seen installed in Prius are mostly Denso.

The Denso plugs also have this shiny plating on the spark plug metal shell. However if you don't take the plugs out until 120K miles you may find that they are stuck.

So, even if you decide not to use antiseize lube it would still be a good idea to remove the plugs periodically (like at 60K miles) just to make sure they can be removed without major drama.

 

The motor should be cool. Aluminum expands more than steel therefore the spark plug hole will get smaller and tighter when the engine is hot.

Typical Coefficients of expansion:

titanium 1.00
cast iron 1.21
steel 1.63
stainless 1.63
gold 1.65
bronze 1.88
copper 2.04
aluminum 2.73


It typically takes way more than 13 ftlbs to break plugs loose. Typically something closer to 80 ftlbs.

I have pulled plugs from some very high mileage aluminum blocks with no issues. A number of years ago I helped my brother change the plugs in his 3 cylinder Sprint with 110,000 miles on the original plugs.

The original platinum plugs on my Toyota Sienna were changed at 100,000 miles with no issues.

 

We can debate that but definitely remove the sparkplugs with the engine cold.

How to Change the Spark Plugs on a 1992 BMW 318i | eHow.com

How to Change Spark Plugs in a Car - wikiHow

 

Ok, the hole will get larger but the dimensions of the threads in the aluminum head will also be trying to change relative to the steel spark plug. This will tend to increase the tension in the spark plug similar to the effect of increased torque.

Also both the plug and the threads in the aluminum head will be softer when hot.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html