B.C.

Greetings all:

This question is technically related to a Toyota Corolla I own but figure it is probably relevant to our Maximas as well.

1) Do OEM spark plugs (such as Nissan or Toyota) come pregapped for the intended vehicle? I picked up some for my Toyota and was told by the parts counter man (confirmed by the mechanics) that they are pre-gapped and ready to go. When I got home, I checked with my gauge and they were all about 0.028" compared to my owner's manual and FSM recommendation of 0.031". I went ahead and installed them as is since they were so adamant about being told by Toyota that they are "ready to go". I also didn't know if perhaps a TSB had been issued that had changed the gap setting from what I read in my manuals. Besides, the old ones (probably due to electrode wear) were all around 0.040" and the car was still running fine so I figure a few thousand's of an inch either way is not too detrimental. What do you all think?

2) If one desires to periodically check the condition of the plugs, is it acceptable to re-torque the plugs even though the gasket has already been "crushed".

Thanks!

Daniel B. Martin

1) The NGK original equipment platinum plugs for our 4Gen Maxima engines come pre-gapped. You may like to check them at installation time. The correct gap is 0.039"-0.043".

2) With the exception of gross damage you can't really tell anything about the condition of a spark plug by visual examination. You can tell something about the condition of the cylinder by looking at the plug. This is called "plug reading" and it would be done only as part of a diagnostic evaluation of a malfunctioning engine.

You will find photographs of spark plugs with explanatory text at several web sites. Here are two good ones.
http://www.centuryperformance.com/spark2.htm#Reading
http://www.nightrider.com/biketech/spkplghnbook.htm#We

bill99gxe

iTrader: (1)

Thanks, Daniel. Info has been FAQ'd into the Spark plug change post in the Maintenance sticky.

sinewave

Daniel,
I have read in several places that you should use a special plug gapping tool for platinum plugs so that you don't damage the fine plat. wire. I hve checked at all of the part stores here for one and everyone looks at me like I'm crazy. Do you know if they make such a tool and where I could get one?

B.C.

Anyone have any comments on re-installing a spark plug with a "crushed" gasket? I would think this would be ok especially using a torque wrench.

Daniel B. Martin

I haven't come across a plug gapper identified as special for platinum plugs. I think the key feature you want is a tool which adjusts the gap by bending the ground electrode without touching the center electrode.
Example of what you want: Kastar #2633A.
Example of what you don't want: Kastar #712C.
See both at http://www.kastar.com/gauges.htm

sinewave

I've used the wire type gauge for years but it still contacts the center electrode. IIRC, the platinum type should have some sort of forked tip that goes on either side of the platinum but is still supported by the tip.

B.C.

Daniel:

I read your installation instructions for spark plugs in the "sticky maintenance section" and was wondering about your "dab of antiseize" recommendation. I coated the grooves of my spark plugs from top to bottom with anti-seize (made for spark plugs) and then wiped off the excess with my finger such that only the grooves of the threads were completed filled with the compound. I was wondering what happens if some of this material works its way up the thread during installation onto the gasket surface and hence where it sits against the head. Will it harden there or be able to be cleaned off when it is time for another set of plugs?

Thanks by the way for the excellent links on "spark plug reading".

Daniel B. Martin

What you did was fine. Anti-seize will never harden. The concern about using just a dab is that anti-seize is one of the substances which will "poison" an oxygen sensor. A careless technician might put a generous gob of anti-seize on the plug and some of the excess would find its way into the combustion chamber and ultimately to the oxygen sensors.

B.C.

Daniel:

I have done some internet reading since I last posted and some claim that anti-seize provides lubricity to the extent that over torque is possible. However, the old plugs were pretty "frozen" so I guess it's a matter of whether one feels over-torque is possible vs. the benefits of getting them out easily in the future.

I did note that none of the new plugs required over 1/2 turn past finger tight to reach specified torque so this does seem a reasonable amount of tightness without over-torque wouldn't you think? Have you seen any guidelines for plug tightening on a purely "degree of wrench turn" basis?

Thanks!

Daniel B. Martin

This is true for any kind of lubricant. I believe that the factory torque spec for spark plugs assumes the use of anti-seize.

In the days of cast iron cylinder heads this was acceptable. Modern engines, including the VQ30DE engine in our 4Gen Maximas, have aluminum cylinder heads with relatively fragile spark plug threads. If you have years of experience changing plugs then you may have developed a "calibrated" feel. That is acceptable, but I prefer to use a torque wrench.