IIRC, my 1973 Triumph GT6 had no valve stem seals. Said right in the Owner’s Handbook that the car was designed to consume oil. That stuff went away when we all got concerned about emissions.
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Very interesting, Kirby. As part of my r/r of the camshaft/valve cover seal, I installed a new hose clamp on the PCV system hose that comes off the top of it. The old clamp had cracked and broken in two some time ago, apparently. Something in doing all this maintenance must have had a positive effect on what i thought all this time was an exhaust valve stem seal leak, as since then I do not have the intermittent “blue puffs” out the back end at start up anymore … 
Now I’m really confused. 
I thought for sure we had exhaust valve stem seals on our 4.0s … ? In fact, I even priced a set on Ebay some time back when I was trying to line up a tech to do the r/r work. I remember reading a post in the archives about how a member replaced theirs using the “air compressor trick” i.e. blowing compressed air in through the spark plug hole to hold the valve up and in place while the seals were switched out). 
According to the drawings and parts information on Jaguarclassicparts.com, the Jaguar XJS 4.0 liter engine has Inlet Valve Seals but no Exhaust Valve Seals.
I don’t own any Jaguars with that engine so my information comes from the Jaguar website.
Paul
There are two different 4.0’s in the XJ-S, the AJ6 and the AJ16. D’ya suppose both engines have valve stem seals on the intakes but not exhaust? Or might there be a difference between the two engines? Anybody know?
I just looked at the Classic Parts website, and for the AJ6 it seems to show seals for the intake valves, but none mentioned or shown for the exhaust valves. Question then is, what is causing the blue puffs of smoke out the exhaust on occasional start-ups (only) of Superblue?
The exhaust valves are on the down side of the engine so on shut down the positive pressure in the exh manifold ceases and that allows oil to seep down the stems as the oil sits slightly above the guides.
So, might adding valve stem seals to the exhaust valves on the AJ6 be a way to address this puff of blue smoke on startup? Anybody have any idea what valve stem seals might fit?
Like most (if not all) seals they were good for about 50,000k and by then the had hardened up and become ineffective.
The ones in my '83 V12 had about 65k on them, and they were still soft. The problem was that they had swollen to perhaps 120% of their original size, meaning they fit loosely on the guides and didn’t even touch the valve stems. I think that was probably due to the material interacting with the oil, or perhaps additives within the oil. I had been using Mobil 1 synthetic. Note that some lubricants have additives intended to make elastomers swell a bit because in most cases – such as O-rings – a little swelling makes them seal better. But in the case of the OEM Jaguar V12 valve stem seals, swelling just made them loose and leaky.
The OEM seals are also just plain rubber. Both the teflon seals I installed and the Viton seals being discussed have metal springs intended to hold the seals securely against the valve stems regardless of swelling. They both also have metal collars at the base to hold them securely on the guides.
If your valve stem seals get hard, it might be age or exposure to oil, but I kinda doubt it. IMHO, it’s more likely that some overheating has occurred. Heat is what usually makes these rubber parts get hard and brittle.
If it runs rough on start when the smoke occurs, could possibly be a dripping fuel injector. The raw gas can wash down the cylinder, temporarily causing rings not to seal well.
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Agree. heat messes up rubber or similar materials used as seals. A factoid to Corvair folks.
If it tosses a belt, it will get hot. And, if the engine survives, it will be a “leaker”. Was there with my 63 Camperized Vair van. Changed out the pan gasket, valve cover gaskets, and valve tube gaskets. got most stopped. -
Most think that the “snake oil” used to stop hydraulic leaks in steering and auto boxes is indeed a sealer that works by swelling seals. The trouble is that some just keep swelling til the seal is gone… So, add the snake oil, let it do it;s job. Then flush and refill with clean oil.
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Either my jaguar is weeping or my daughter’s Nissan is spotting my drive???
I know my Jeep weeps. Rear main or valve cover. Not enough to concern me, surely not tackle a fix. Valve cover sounds easy on it’s straight six!! Not so, most is under the cowl!!!
It rarely needs a QT. to top it off between changes.
Just went out to provide Billy his favorite kibble. He does not mind the awful tasting meds added !!! His dish, the top of a waste barrell. perfect. He is messy eater. And during the day, he will butt the can around trying to get it to produce more of the treat. .
Seem like some human trait. Keep butting one’s head against the wall. But, he ahs an impressive set of horns that we lack!!
Carl
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My 97 Volvo 850R is burning 1 qt a month, I would say half of that is from valve stem seals. They are original OEM viton. Problem is, the turbo heat is what eventually makes them rock hard. I will need to pull head to service them.
On the V12, does the heat of the Vee not disrupt the valve stem seals as much? Or is the Vee heat much less than what a turbo would put out?
Many years ago I had a chance to look over a Winston Cup car pretty closely. Those things hold close to 200 mph for a couple of hours at a time, and they had learned a thing or two about dealing with heat buildup. One of the problems was that the valve train would overheat; the valve springs themselves would get hot. Their solution was fascinating. They had two oil coolers up in front of the radiator. The main supply of oil from the oil pump would go into one cooler, actually the second cooler the air gets to, and it’d get down to a reasonable oil temp. After that the oil feed would split, and part of it would go to the galleys to feed the engine bearings. The other part of the oil flow would go into the other cooler, this one being the first thing the air sees so it gets the coolest air. That cooler would get that oil as cool as possible, much cooler than is usually wise to run motor oil. Then it was directed to the valve covers and sprayed directly onto the valve springs to cool them. Then it’d just drain back into the sump.
So, you wanna get your turbo’d engine to quit cooking valve stem seals? That’s probably how to do it. Or I suppose you could just replace them with Teflon seals, that might work.
wow, that’s interesting. Well, these valve stem seals usually go 125,000 miles until they start leaking, so I think I’ll just replace them, and I make sure to run synthetic oil. Will be much cheaper/easier. 
Still curious about the V12…I assume this heat problem everyone talks about with the Vee is mainly an external problem due to it’s oven like structure? If your coolant stays under 190F, then the oil is also being cooled properly, so the engine internals aren’t being cooked?
The Jaguar V12 has a couple of unfortunate design flaws that tend to lead to overheating, but when it’s running as it should it doesn’t run all that hot. In particular, the cam boxes run with little pools of oil on the tappets, so all in all everything in there should remain within reasonable temp limits. That’s as opposed to turbo’d engines which often have exhaust manifolds that glow cherry red when running and tend to really cook right after shutdown. I recall a Mitsubishi turbo that came off the showroom floor with a tiny electric fan in the engine compartment that would blow directly onto the turbo housing for a few minutes after the ignition was shut off.
You might note that the Jaguar V12 originally came with bypass oil cooling, which means the hotter the oil gets the less oil goes to the cooler. That didn’t work on the Autobahn, so Jaguar developed a full-flow oil cooling scheme – and fitted it only to cars sold in Germany! Eventually they fitted it to all models, but it took them a few years.
That Winston Cup car also had a diff oil cooler. The fill and drain plugs in the diff were replaced with AN fittings with hoses connected to a small oil pump driven by a belt running around the drive shaft itself, and then to a small oil cooler under the car and back to the diff.
In the XJR-S, the diff likewise has improved cooling, in the form of a finned rear cover. The shape of the cover on the inside of the diff supposedly helps direct the oil spun off the ring gear to circulate better to stay cool.
Billy the goat, Carl?
That’s a thought, Kirby, and, IIRC, something that came up on the old J-Lers board some years back, but IIRC it had to do with the XJ40 (which I presume also did not have exhaust valve stem seals ?)
Same engine, so I’d presume so. I doubt if the valve stem seal situation would have changed when the AJ6 went from 3.6 to 4.0.
Yup!
He is a guest in my back forty. His former home was in my son’s Sierra. But, as he is getting along in years, fighting off predator mountain lions or coyotes becoming an issue. An Alpine wether of about 10. At least 200 pounds and strong. Plays “rough”, I gotta watch out.
Carl.