One thing I always noticed over the years was the "bubbling" condition of the 4.0 Ltr magnesium valve covers. When I bought our 97 XJ6L (62K) I found it interesting mine was pristine. About two weeks after buying it I pulled the cover and replaced the gasket and upper tensioner and my coil gaskets crumbled apart. I asked my friend who is a jaguar mech what he does and he says he just doesn't use them so I trusted his judgment and went without (wells were nice and clean too) now 1.5 years and 10K later the valve cover is a mess of bubbling and the wells show signs of arcing. My boots seem to be in super good and pliable shape so today I siliconed the joint point of the boot at the top, made my own gaskets and applied liberal dielectric grease at the base/boot opening. I've seen it discussed here before that there is two sides to the gasket vs non-gasket application but after what my valve cover has become w/o I'm convinced they are needed plus excessive arcing will surely cause premature coil failure.

 

I think those paper gaskets are more of a dust seal than anything else. One theory I have for the bubbling of the paint is condensation on the inside of the valve cover due to short runs. Those mag covers are not very high quality and condensation could result in electrolysis.
It would be interesting to hear from others as to drive cycles and cover damage.

 

Sorry, I'm not buying that condensation didn't happen for 16 years and 60K.

 

When differing metals come into contact with one another, they have an in-built emf (electro motive force) which can lead to galvanic corrosion. Could it be that the gasket reduces this emf and hence corrosion?

 

Just FWIW, on my '95 (154k miles) the cam cover has only minor bubbling....and had none at all until 2-3 years ago. Not that I've kept notes on the subject but at least half that mileage was accumlated without the coil gaskets.

In fact, it's only been the last 2 years or so that I've had gaskets....thanks to so many coil replacements.

I'm not a metalurgist so I can't speak with any intelligence on the matter. However, judging from the above, I'm not convinced that the gaskets are significant WRT the cam cover bubbling issue.

Cheers
DD

 

Either way I wish Jaguar would have come up with a better cover. Most I've seen look terrible.

 

My XJ6 didn't have gaskets on the coils. I have owned it for 2 years and don't know how long this has been the case, but the cover is in very good shape. I think the corrosion/bubbling is something of a hit and miss/pure luck thing. So many variables as to climate, humidity, type of driving, spark plugs, condition of coils, electrolysis, cover manufacture variations, etc. etc. I think it might be a hard to quantify and get a definitive answer on.

Just my thoughts..................

 

Now that everybody is talking about it my are not in the greatest shape either. What would be the best way, short of pulling everything off for a paint shop or powder coating?

 

And while we're on the subject, the cover on my donor car is in pretty good shape too, as it's a 3.2 and is marked as such, it's not a lot of use to me, given that my DD is a 4.0l. So I have a good cover up for grabs if anyone is interested. Cover the postage and it's yours and maybe promise to do a good turn or put some change in a collection box of your choice?

 

You have a PM. See my valve cover in the pictures below - more than bubbling but badly corroded around the spark plug wells. The heat and humidity in Hong Kong, and a leaking valve cover gasket may have added to the electrolysis or corrosion process.

 

HI all If I new how to add a photo to this I would. My XJR has 198k around 120k miles and most of those are mine , My cover is blemish free and it is still The the original cover . it has always had gaskets for the coils, and for the majority of it life has only used synthetic oil which is changed regularly irrespective of miles done . I have seen many in poor condition and the only difference that I have noted is I don't use mineral oils . May be I am just lucky to have one that looks perfect inside and out . For show purposes it has been repainted but its current condition is 5 years since this was done. I will try to put a photo up
Rommel

 

Jaguar engine valve cover was manufactured with material defects, much like the Mercedes Benz W124 body engine covers. material use was not capable of high temperature and neither are they properly adhere to the cast magnesium alloy and iron metal material.

Was laughing at the many ridiculous reasons and amaze by the how jag owners can come up with non scientific reasons for the corroding paint, adds humor to the blog hahaha

Only way to restore is to have it powdered coated with material that can withstand up to 4500 degree Fahrenheit, manifold spray paint can also do the job.

 

"Humor"? Re-read this and think about that.

 

not sure wether that is supposed to be sarcastic on not ( Re Read this ) but what I have is what I said. I agree that the cover is made of substandard material for its application the only comment that I am making is a casual observation that I don't use mineral oils and my cover is as new, for a recent photo go to www.jagqld.org.au go to resources and magazines march magazine page 37

 

Unlike the exhaust manifolds which have a common cracking problem regardless of global locations where we drive our X300, why some valve covers stay unblemished whereas others became cooked like mine remains a mystery.

Maybe all those that turn ugly were manufactured on Mondays (LOL...), or something unusual happened or did not happen at the production or assembly line (like temperatures in the O-ring saga in the Challengers).

The one on mine (1995) survived 19 years, only turning bad in the last two years. Was lack of regular use or leaving it idle for a prolonged period a contributory factor? Mine was unused for almost 18 months before my takeover, and maybe rarely used long before that.

There is a general belief that powder coating with bake paint would preserve the valve cover. But, for any paint work, the surface pre-condition, paint choice, worksmanship, and maybe surface temperature at the time of the paint job, may affect the durability of the respray. I would be interested to know if there are repainted covers out there that can withstand the test of time - no, not one or two years, but much longer if I were to be convinced.

If folks have any ideas keep them coming....

 

My point IS sarcastic....4500 degrees F ??? Really???? My valve cover doesn't get anywhere close to that hot OR anywhere close to what an exhaust manifold does Which isn't even close to 4500!!!!!!!. Powder coating??? Good luck with that, not very likley most shops would know how to properly do magnesium. Manufactured with material defects?? How so? Based on what information?? Adhere to cast iron??? The X300 cover is magnesium. Mineral oil vs synthetic??? HUH???? I don't even know how to comment on that or how oil on the inside reacts with the outside (if that was a factor my inside of the valve cover would be trashed, it looks new inside)

FYI magnesium is used extensively in the aviation industry and in the wheel industry and in a lot of cases NOT covered by a protective coating I've seen very little if any corrosion on our aircraft's magnesium parts and I've operated in some pretty intensely humid environments many of our parts are also "allodined" prior to coating which is a chemical etching process (similar in some respects to anodizing). My car spent it's life in Florida...60K no corrosion/bubbling what so ever....10k w/o coil gaskets and having boots disturbed....plenty of bubbling and arcing paths in and outside of the wells. I see plenty of "ridiculous" reasons...all that are outlined in the post I quoted. Anode/cathode reaction can be accelerated by influence of electrical current which could be prevalent by coil arcing which would in turn accelerate the corrosion process when exposed to a humid environment. By ensuring there is no arcing one in turn would theorize one could eliminate a catylist of the corrosion process. If you think it's defects, 4500 degrees, mineral vs synth....more power to ya, just quit referring to peoples ideas as ridiculous until you really look at how your own ideas look.

http://www.magnesiumsquare.com/index...d=27&Itemid=42

 

Of further interest to me (I have both) is my 02 Lincoln LS and 06 Mercury Mariner. They both have a 3.0 both the Lincoln LS v6 and V8 were joint ventures with Jaguar (S type particularly) Both have similar COP's and neither have coil "gaskets" and both the V6 and V8 have "plastic" valve covers not Magnesium in which the coils fit to. Now why didn't those engineers fit paper gaskets to those? In all and in closing I wish no ill will or malice to anyone who shares their $.02 on the subject....any ribbing are sarcasm on my part is all good natured and not meant to hurt anyone's feelings (Ok, I really don't care about your "feelings" but I at least don't wish ill will)

 

Yeah. The idea that any part of the engine gets to 4500 degrees F is pretty outlandish. I would like to know where that idea came from. Am I missing something? And as to the paper gaskets- What would they be insulating? The valve cover from.... the plastic coil case? As to mineral oil, ozone from electostatic discharge and so on, I cannot comment.

 

If folks go to eBay UK (try "rocker cover" / "valve cover", "tapper cover", "cam cover") there are many used valve covers removed from scrapped X300 or like models dating back 1994-1997, and all those still look in reasonable state. So if choosing between whether to recondition a bad one I would rather go for a good used one, in the hope that if it can stay in shape for the last 20 years or so, it should stay that way for many years to come.

 

Bravo, except for the part when i said using 4500 degree paint does not mean your valve cover will reach that temperature, it just said using the 4500 degree spray paint to paint your valve cover, wondering whether you knew what your reading or your emotion is clouding your thought.