Checking the PCV Valve / Serious Engine Oil Leaks

Well, despite using all kind of stop leak products (which I used with great success on my recent blown head gasket, incidentally) on my serious engine oil leak situation w/o success, I’m again thinking that the problem might be a bad/stuck PCV valve that is forcing oil out at various “weak spots” in the engine (i.e. where gaskets or seals exist). The only other plausible explanation would seem to be a rear main oil seal leak, but it is my understanding those are very rare on the AJ6 engine. Further, one of the sealer products I used (Barr’s Leak’s) was especially for same. :thinking: In any event, you can see the leaked oil at various spots on the ground under the engine after running just a few minutes, and it appears to be coming from some point(s) south of the cylinder head. If there were an oil hose anywhere in the system, I would suspect it was blown or loose, given the amount of oil she is losing, but AFAIK there aren’t any. Checking the engine oil cooler assembly shows no sign of a leak there, either (i.e. lines or o-rings).

So, is there a simple test to tell whether the PCV valve is working properly? I have heard that, in general, there is a “stamp” test to tell whether your engine gases are circulating properly around the crankcase. This involves placing a postage stamp over the open end of the dipstick tube with the engine running. There should be just enough vacuum at that point to hold the stamp firmly to the end of the tube. If the stamp won’t stay in that position and just falls away, look out. :grimacing:

Well, doing a little research since my original post, I find out that indeed a bad (stuck) PCV valve can cause major engine oil leaks, as well as other gaskets (possibly even the head gasket on an AJ6? :open_mouth: ). There is a crude “blow” test to determine whether it is blocked, and apparently they can be cleaned up if blocked. I would like to buy a new OEM one, anyway, and it appears they tend to run about $100 or so for the AJ6 version. Anyone know of a cheaper source, possibly?

Now I have a question about the EGR valve … If it is messed up, can it cause similar problems with the engine as a bad PCV valve? Can they be repaired/cleaned, if bad? btw, they appear to be another $100+ replacement item for the AJ6. :confused:

A stuck pcv is definitely bad for engine. It can and will blow out oil seals. Most times a Pcv valve can be cleaned with brake cleaner and work again. Sometimes once those seals are blown out, they need replacing. If its just a small drip, a working pcv can reverse the leak.

But you make it sound like its a big leak, below the head? Make sure its not valve cover, as those easily leak big and need replacement. Mine was, even with a fixed pcv system.

If you’re sure it’s coming from head, well, head gasket could be leaking oil too, not just coolant. Could be blown between oil passage and outside of head?

Clean things up and determine exactly where oil leak is.

1 Like

I thought about the valve cover, but I replaced it about 3 or 4 years ago and there has been no signs of leaks from it to date (esp. at the rear, or the “half moon” seals). I do wonder if the blown head gasket and the oil leaks are related. I do know the one thing that the manuf. mentions in their literature is that their product will not seal up an oil leak to the outside of the head (b/c the oil “lubricates” that area and won’t let the sealing particles - e.g. carbon fibers - stick in that area and seal it off). Hopefully I will get to the bottom of it soon. :crossed_fingers:

Atty, Greg,

Not sure if you noticed, AJ6 engine has multiple, continuous crank’s backpressure extraction points… Just saying.

( look at the hose on top of your 6-banger - connected to air inlet’s elbow boot).

If the above still doesn’t sound clear, I advise Tolkien’s LOTR series…

Janusz is right. There is a giant hose at the camcover that should be more than enough to depressurize the engine directly into the intake elbow…and into the butterfly where you should clean that gunk out annually…or something like that.

I am not aware a PCV even exists for the AJ6/16 engines.

1 Like

Clean the engine as best you can. Remove the hose from the valve cover to allow crankcase to vent to air. Drive the car.
If leaks stop or is reduced significantly, then the PCV system is defective. If no change then make a trip your local church and drop something into the collection plate.


I didn’t know that was a way to soak up all the oil that Jaguars shed. Does the church recycle the oil from the oily rags dropped into the collection plate?

1 Like

There is no PCV system on these cars…there’s that weird egg separator, but essentially the crankcase vents straight to the intake elbow.

Wow … News flash there :open_mouth: btw, “egg separator” ? :confused: And I’m still wondering what the EGR valve is for … ?

Egg separator was a concept that Jaguar used to attempt to keep the intake butterfly from gumming up. Bad idea which didn’t work, btw.

There is no PCV “valve” in the system, but there is a Positive Crankcase Ventilation system in the vehicle. BTW I do know what you meant. (Smile)

So is that gizmo actually on our AJ6 engines, or was just an “experiment” by Jaguar? :confused: I’m also thinking that this arrangement (i.e. the crankcase blow-by going into the intake butterfly) is why it seems there is always a shallow “puddle” of used engine oil in my intake “accordion” when I remove it to clean up the butterfly valve/throttle plate. :angry: That may also be why Superblue blows, in part, her blue smoke sometimes at first fire up in the a.m., as she has always done since I have owned her. :thinking: