Hi everyone....

Well, it has been almost 6 weeks now since I have had to replace a failed coil pack on my 2001 XK8....

I have found the Denso packs to be the most reliable thus far, and after replacing 9 no-name brand packs over the last 14 months since ownership, my friend who owns a local garage recommended I remove the covers over the coil packs to allow the heat build-up to escape and should offer some longevity to the coils.

He tells me he's worked on some Volvo and BMW vehicles that suffered the same premature coil pack failures and the cover removal has been the common cure.

Here in the Florida sun and high temperatures, it actually makes (some) sense.

Has anyone besides me actually tried this or heard of this recommendation?

Your input is appreciated.

Doc

 

It might be OK on an XK8, but it would be a disaster on an XKR with hood vents in the rain!!

The Denso (OEM) packs are pretty reliable, it probably should not be necessary.

Do you have any oil leakage in the spark plug wells?

 

No oil leaks in the plug Wells on either side, although the right valve cover bottom rear has a slight drip on the exhaust manifold. Next project to tackle...

When I got the car in Dec 2011 it had a skip in #7 then one in #4 and weeks later #1, and #5 as time went on.

The guy who owned the car before me had replaced all of the coils in July of 2011. That was 5 months prior to him selling it to me. He'd bought the could from Welsh in Ohio for $60 each. I found the receipt and Welsh honored the 1 year warranty and sent me 4 replacements. Those all failed over the next 3 months.

Found some Denso coils from a junk yard for $20 each and haven't had a failure yet. But this was also after removing the covers.

Coincidence? Perhaps.

 

Here in Tucson the summers are much hotter than in Florida with many days well over 100F. My '99 XK8 has 112K miles. I recently changed the plugs and had the opportunity to inspect the Denso packs which I believe are original. If not, I can for sure say that they've been good for over two years and 20K miles.

Point is, I personally wouldn't suspect heat being a problem unless it is the no-name packs are inferior and can't handle harsh conditions. I'd go with the Denso and put the covers back on. There are some pretty delicate wires being protected in there.

All that said, if (when) I do replace coil packs, I'll remember this information. So thanks!

 

Thanks for your input... and I've hear the Denso are pretty decent.

The engine looks naked without the coil covers on it, and I'm considering adding some spacers on the cover screws as a precaution to allow heat escape anyway.

The could always seem to fail while sitting at a traffic light and the dreaded Restricted Performance message pops up. I've had two fail at the same exact time in traffic after exiting the interstate too. I limped the vehicle home that day.

I keep an OBD reader in the back seat pocket. I've used it a lot!

Denso it is... I've seen them new for $40 on
eBay. Autozone has them for $115. Ouch!

 

Instead of leaving covers off why not just cut 3 large holes down the center. This way wires are still protected along bottom edge but better cooling.
Just replace 1; bought new at Auto Zone (Spanish Denso $129) and ordered spare (Prento $48) from Parts Geek made in China.
XK8 has 64K on it.................wife loves it still.................
2007 XK Coupe too but with 2 BU lights!

TTFN, Adrian

 

Adrian -

My first thought was to punch some vent holes in the covers, but common sense got the better of me in the event I ever sell it, yes it would be functional maybe, but aesthetically a turn off to a potential buyer.

Locally Advanced has the Densos for $128 and Autozone for $115.

The coil packs are similar in design to something like the old MSD ignitions we put on our coil / distributor gas engines. I undertstand each coil has a circuit board with something like a capacitive discharge components would have that actually fires the coil windings to produce the high voltage. I have not cut one of my bad ones open but it makes good sense theyre built that way. The ECM does not have enough to directly fire a coil. The electronics in the coil pack seems to be the heat failure culprit. If not shorted coil windings itself.

When I break one open I will confirm this.

Thanks,

Doc

 

When you break it open you will find something missing ... the oil bath.

The old coil and coil pack systems had oil baths to do the cooling and were much bigger. Miniaturisation forced the ellimation of the oil bath. No more oil bath cooling.

 

We used to call that transformer oil during the days I was in broadcast engineering.

With said state power supplies the elimination went along with common tube type radios.

And car generators and regulators...

Thank goodness.

 

Except that you now have a suspected cooling problem. Easily addressed in a conventional separate coil system with a bigger coil or relocation. Not so easy when on top of the plug tower.

The windings did not go away despite the change in method for collapsing the coil field. The method only applies on the 4 wire COP by the way. The 2 wire cop still does it the time tested way of circuit interruption.

 

I can hardly believe that you have had this much trouble with the coils. In my experience, the coils are more suceptible to failure if they are over-worked. I have seen it on Jags, Benzes, BMW's, GM cars, etc. That being said, how old are your spark plugs? Are they gapped correctly? Worn plugs with a wide gap are likely to overload those coils, possibly causing premature failure. I live in AZ, and I don't see failure due to "heat" on any regular basis.

 

I live in Vegas and during the winter months, I have never had a coil fail. In summer, especially this year, when its 112 and up, outside, engine compartment probably close to 200 degrees +, I kill a coil or two a summer. I like the idea of leaving the covers off. I just replaced #6, will leave the covers off and see if they make it through summer.

 

Thanks for the note....

I actually put some spacers under each screw lifting the cover off just about 1/4 inch or more. It seems to let the coils run cooler with the heat escaping.

It looks better, and I haven't had one fail since.

I also just sold the car 6 weeks ago and bought a Ram 1500 lol

I've missed owning a truck. Yet I miss the Jag now too!

 

Huh?

 

All of your recent failures have been infant mortalities so-to-speak. If you want some trouble free, used, OEM coils with probably less than 50K on them, I'll let them go for $25 each +shipping. They've offered up no problems at all in a Black XKR that routinely takes long trips south, "deep" into Florida. I have a set of eight on hand. Anyone interested, just PM me.

Ciao!