On the XJR6, and I assume the normally aspirated AJ16, the crankcase vent hose comes from the valve cover and then splits into two. You can see that here:

https://www.jaguarclassicparts.com/u...-3-2-4-0-litre


On the XJR6, the larger of the hoses connects to the low pressure(prior to throttle body and SC) duct, and the smaller hose goes directly to the throttle body (TB).

As we've found, this arrangement introduces a lot of oil into the intake tract and eventually gums up the TB.

So I'm wondering if that direct connection to the TB is necessary, and actually may be a detriment? I wonder if one could just plug the TB nipple and remove that smaller "Y" in the hose with no adverse effect? This would still leave the larger "Y" in the hose connected to the larger intake duct. Any idea of impact?

Makes one wonder why the split and direct connection to the TB was even designed that way anyway.

I plan to also put an oil separator can on later, but always looking for opportunities to simplify things (less complex hoses) and maybe right a wrong (introducing oil directly to the TB throat) if possible

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A question I too have pondered over, however the small hose is connected to the Throttle body for a reason apparently.
I have attached relative page dealing with this smaller, part load breather hose.
I actually have the engine coolant hoses disconnected as they are not required in our warmer climate, the heating is there to prevent icing during cold weather. This was the topic of a recent thread.
If you choose to disconnect it would be interesting to hear if your driveability is in any way affected.

John Herbert
(1996 XJR)

 

I have disconnected this for years and never had problems.

 

Thanks for the feedback.

It's interesting how relatively more complex the breather system is on the NA cars with the special valve, etc and on the SC cars it is just a direct hose into both the intake duct and TB.

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standard no difference, no valve. Red dotted line is coolant, goes to throttle body

 

That's true, the white "valve" I was referring to is really a "coolant heated restrictor" per the PDF linked above, but no such restrictor body exists for the SC car, which I find interesting.


Anyway, now that I've got the TB off, I can see that the smaller TB vent hose dumps out into the SC bypass manifold directly behind the TB, which may explain why the SC TBs are so oiled up on the backside of the butterfly. With that small hose and high vacuum, it might be creating quite a suction and pulling in more oil than the big hose that goes to the duct upstream.

I can only assume this small hose terminating behind the TB allows crankcase breathing when at closed throttle like idling. You would think this wouldn't be necessary though as the idle air bypass control motor allows air past the TB butterfly when the throttle is closed.

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Anyone else have any thoughts or experience on this topic?

I've got the intake back together, so planning on the oil separator.

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Yes, I installed an ADD-W1 aftermarket oil separator ( the stock Jag separator is junk) in the cam cover hose. I also "T" in the small vacuum hose to help pull the fumes out of the cover. I love the results of all the crap the can collects that don't go into the throttle body

 

Got the catch can installed this weekend, and based on the feedback above went ahead and plugged the small hose that branches off and connects to the TB, dumping oil right on the rear of the butterfly.

So far plugging that hose has had no noticeable effect. So I'll leave it plugged unless something comes up that changes my mind.

I also heard from "Moff1959" who had installed a catch can and also plugged the small hose and ran it for some time with no noticeable ill effects.

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Wait a minute...

You installed a catch can, so you ran the line from the camcover to the can...then from the can to...???...

I'm not sure I understand what you did.

 

I installed mine on a non supercharger 95 6cyl . The hose comes out of the cam cover to side "in" of the catch can, Attach another hose to "out" of the catch can and run it over to the throttle body. I think I used 5/8 or 3/4 inch heater hose .
Now that left me with a small vacuum hose coming out of the EGR valve area, (I don't know what its for) I "T" it into the "in" side hose, (cam cover to catch can).

 

Catch cans are inserted in-line on the crankcase breathing vent hose that runs from the cam cover to the intake tract.

The intake creates a vacuum that depressurizes the engine block and also removes blow-by gases. In decades past, this was just accomplished by a crankcase breather and/or PCV valve.

I can't speak to the plumbing of the NA XJ6, but for the SC car there is an approximately 3/4" diameter hose that connects to the breather nipple on the cam cover that then splits into an approximately 3/4" hose that connects to the intake duct that wraps around the intercooler ahead of the TB, and a smaller approximately 1/2" hose that splits off and connects to the TB directly.

You can see that hose in the diagram linked below, part #1:

https://www.jaguarclassicparts.com/u...-3-2-4-0-litre


So, ignoring the 1/2" hose that this thread is talking about, and I've plugged, you insert the oil catch can between the breather nipple on the cam cover as the "inlet" to the catch can, and the "output" of the can then goes to the connection on the intake duct. The can now intercepts the oil vapor as it is sucked out of the cam cover before it is sucked into the intake.

You can see in the photos above how another owner mounted his can on the left side of the NA engine, and used heater hose to extend the factory connections to the can, which is also what I've done except mine is mounted on the right side of the engine.

If that still isn't clear, do a quick Google on "oil catch can install(ation)" and there are a bunch of photos and videos. The all install the same way on any car.

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I'm clear on the catch can install, I have one on my car. The NA AJ16 is simpler, and I don't have a vacuum hose connected to the EGR, so I guess the XJS is still a simpler assembly.

I was not aware that you guys had a vacuum tied to the EGR, I always assume that everything under the hood, mechanically, is the same.

 

I do not have vacuum tied to the EGR on the SC car, nor do I think there is on the NA car. The diagram I linked above for both the NA and SC car doesn't show any hoses connected to the EGR.

The catch can doesn't have any interaction with the EGR. Not sure how EGR came into the conversation other than "44lawrence" comment above. I think he may have mis-spoke or maybe just meant a vacuum line was in that area. I suspect he was really talking about the smaller line that splits off and goes to the TB, not EGR.

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Sorry I didn't look close enough @ that vacuum hoses location.
Looking from the pass side (USA)under the injector cover its the closest hose to #4 injector (there are two small vac hoses there). This is a Non Aspirated car. If you don't use this hose as I did, using the catch can, you have to cap it off. I figured to put it to some use

 

Yes 44Lawrenxe confused me a bit with his reference to theEGR.

I think we're all on the same page now.

I placed my catch can between the throttle body and camcover, it may be too hot to do its job well. I caught a lot of water in the winter time, but recently I haven't caught as much at all. I may reposition it.

 

Well, I've had the little "secondary" hose to the TB plugged for a week now. So far I can't tell any difference, idle remains where it should be, and no CEL is lit yet.

If anything changes I'll provide an update, but so far I'm going to add my vote to say it is OK to plug that hose and avoid oil vapor depositing right on the back of the TB butterfly.

It also makes adding an oil catch/separator can a lot easier to avoid having to integrate both the larger main breather hose, and the small secondary TB hose.

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You can see the final separator catch can assembly that I installed here:

https://www.jaguarforums.com/forum/x...7/#post1708029

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That will work good, mainly in colder damp weather. The after market can's work so much better than the junky contraption Jaguar sold.

 

Over a month, and still no known ill effects from plugging the small hose or equivalently capping the nipple on the bypass body.

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