Just put a new set of Bosch Platinum +4 plugs into my XK8. The dealer wanted $350 to change the plugs (installing NGKs) but for $51 bucks this got me a longer lasting plug and saved me money on labor. This was not a difficult job, for anyone wondering about removing the coil packs, etc.

The only slightly difficult part is removing the rearward screws on the driver side coil pack cover. The lower rear screw is hard to get at and if you are not careful you can break the fragile (plastic? fiberglass?) coil pack cover, as I did without much effort. The good part is that it is easily fixed with some epoxy.

One thing is the oil in the plug well. This I suspect was leakage over time from the valve cover gasket. There was not much oil in each plug well as you can see from the photo. I think the only way to fix this is to swap out the valve cover gasket, which I did not think was necessary given the absence of other leaks or obvious signs of trouble (no oil consumption, etc.)

Any thoughts on this? Thanks.

 

I dunno Burg, that plug looks nasty fouled, and extremely eaten up (look at that gap!). I'd change the valve cover gasket on that side, last thing you need is a future misfire, a coil going bad, then forced to do the gasket later. Leaks don't get better over time unfortunately.

 

I agree. The XK8 I just got was leaking oil bad enough that the plugs on that side of the engine were submerged in oil, and I think that was the root cause of the engine not starting.

 

I think you're both right, the gaskets should be swapped. I'm beginning to wonder what the material looks like around each plug well - must be pretty thin even when new.

The plug didn't look crazy worn out to me, at least not compared to others I've pulled out in years past. I did not have a new NGK to compare it to, though. Hopefully the Bosh Platinums will outlast the last ones. No idea why the ******* thinks the NGKs are better but to each his own.

 

Just an FYI, I have never liked Bosch platinum plugs. Bosch is very stingy witht he platinum, and only use a needle point of it on the electrode. In my experience that burns away very fast, and quickly erodes the gap too wide.

Then again most of my experience with them is with forced induction engines. That is hard on plugs.

 

I used the NGK Iridium plugs. I have them in all my cars now. Reports are that they will out last the car.

 

Is there something special about Jaguars eating plugs? Since we went to unleaded gas my experience has been that they seem to last for ever.

 

There are about four different versions of Bosch Platinums - which one did you use? I presume the more expensive ones might last a bit longer. Then again this could be marketing hype.

 

I agree about iridium plugs. They're used by manufacturers as another "maintenance free" feature in the same vein as "seal for Life".

With the advent of iriduim plugs and modern engine management systems there really isn't such a thing as a tune up anymore, unless you call replacing the air filter/fuel filter a tune up.

Going backwards to a platinum plug or copper plug puts you back into the maintenance game again because, like the old days, these electrodes do wear. I use platinums in my XK8 because I really don't mind changing them more regularly, and, I have a thing about a steel plug in an aluminum head staying there for 100,000 miles, even with anti-seize.

 

I don't remember which ones exactly. The Bosch plugs I got were about the most expensive plugs the local stores had. I thought paying the most meant I was getting the best, and I was wrong. It was close to 15 years ago that I tried them in a supercharged Thunderbird SC. They were the single electrode type, not the +4 or whatever. They lasted about a week, which is no kinds of fun in a car that takes close to 5 hours to change the 6 plugs.

After that I talked with several people with the SC thunderbirds that had the same experience with Bosch platinums. Similarly, when I got into other forced induction vehicles (SVT Lightning, GMC Typhoon) I kept hearing the same horror stories about Bosch platinums, so I never tried them again. There are much better plugs out there at a lower price.

I had the best luck on the SC and SVT with Autolite Platinums, and more recently with the Denso / AC Iridiums. I've heard good things about NGK's but have never tried them personally.

 

I had a friend with a Merkur XR4ti who used them and had nothing bad to say from what I remember, but maybe he changed his mind later on. Well, perhaps in a non-forced induction car they will be better? Will see.

How did you notice the plugs went bad? It must have been pretty horrible performance-wise if you took them out after only a week!

 

The platinum electrodes burned away, essentially working their way back up the ceramic cone in the center. As they melted away the gap wides and becomes shielded by the ceramic. Performance wise I started noticing a stumble / misfire that kept getting worse under boost / heavy throttle.

It might not be as noticable on a naturally aspirated car, but I feel more comfortable with plugs that have a larger surface area on the electrodes. I am suprised your buddy didn't have trouble in an XR4Ti. Was it completely stock? Maybe they don't degrade quite as quick under low PSI operation.

 

I know he did a few things to the car including adjusting the boost upward, but it was otherwise stock. Never remembered him changing out the plugs sooner than expected but who knows, he might have.

Platinum burns differently (cooler) than copper, so maybe some engines need the extra juice. But Platinum is supposed to last longer, but obviously not in your case. Will see how it goes for me with these.