Got the car back from jag today. They replaced the spark plugs, valve cover seals. I've had a ticking noise for a while and car started to die on start up, then start and run fine(worse when cold but constant).

Thought it might be timing based on what I read in this forum. It's a 97 xk8 conv with 127K on it.

Turns out plugs which I changed a year ago. Used NGK iridium and specked for .048 gap. Dealer told me plugs are supposed to be gapped @ .036, only thing is when I took the old ones, they were also gapped @ .048 to .052 except for one @ .038. Problem was that one was almost siezed in the engine with white residue everywhere.

So, what plugs do you guys like and what is the correct gap?

 

I used BOSCH Platinum 4501

 

I've had bad luck (cold starting issues in winter) with anything but the original brand plugs.

 

Well not sure how to respond. Our car is a daily drive with 113,000 mi on it and to date the plugs never let us down and it is not garage kept.

 

OEM plugs were changed at 43k miles to the NGKs (BKR5EIX-11) with considerable improvement in MPG.

Figured that if the OEMs didn't make it to 100,000 miles, which is the Jag replacement schedule, then changing the $7 NGKs every 40k miles or so was a better bet.

 

Hamish
What were the plugs gaped at .045-.052?

 

I'm with Gus here. I use platinum plugs in AJv8s when I can influence the change cycle on cars I service regularly, and I use them in two of my own Jag V8s. Platinums have a more frequent change cycle which I prefer over the 100,000m iridiums, one reason of which is the seizing problem mentioned. Regardless of how much anti-seize you use, it's lucky to get these plugs back out if they've sat in place for 8 to 10 years. Then again, with all the "activity" most all of these engines have seen with tensioner replacement and other things, the plugs have usually been taken out anyway far before 100K.

 

Don't remember the exact gap, but at the time I researched the gap issue extensively and everything I found said to install straight out the box. However, I did check the gaps of each plug as I installed them and they were within spec.

 

I use the iridium NGK's and am more than happy with them.

imho it is not bad to check the plugs now and then in the 100Kmile timeframe, as besides the potential seizing as stevetech is mentioning it is also good to check the plugs themselves to understand more about the combustion, but as long as the plugs are good they go back in.

 

Ditto for me. No problems and mileage has improved.

 

Thanks for the recommendations on the NGK Iridium IX plugs guys, I replaced all mine at 110k miles (original still installed), as the starting was becoming a little rough lately.

After those were replaced, and my throttle body cleaned out (as best as possible, you don't want to see what was (and still is) in the bottom of this thing...you'd faint) the car starts quick and idles smoother.

As a sidenote, on my first drive, the car ran good, but on deceleration coming to a stop, the RPMs never dropped below 1000, and I was getting a hard downshift - like the lurch symptoms. I assumed the fuel/air ratio and combustion was much different than my previous data, so the computers weren't able to quickly fix this, so to correct it, I performed a hard reset, and the downshift issue went away immediately.

 

I use Brisk DOR 15 LGS plugs and I am pretty happy with them. My gas mileage went up averaging on long interstate trips 24 - 24.5 m/gal while cruising between 65 to 75 mph