Water leaking from under head Acorn nuts

Happy to say that after a couple of years restoring the car it started right up the other day. But, as the subject says I had water leaking from under five of the head acorn nuts.

I’ve never restored a Jag of any type, and this has me rather concerned. Do you have any suggestions on how to solve this?

Could you also confirm that the torque is 54 LBS? (SII of course)
Thanks, Pat

I have the same problem plus a small kesk from had gasket. I put in a radiator sealer which is wirking so far. I retorqed head which didnt work. Thaat doesn’t mean it wnt work for you. Yes 54 ft lb…

Assuming you have a long stud engine this isn’t that uncommon.

A couple of cans of Bars Leaks is the preferred option.

Which version of Bars Leaks? The coppery one? The silver one? Or the pellet one? All of which are marketed at stopping coolant leaks

Thanks, but I have no idea what “Bars leaks” is, would a copper crush washer work do you think? I can’t just do nothing and let it leak all the time… can I ?


You might want to not do anything yet to the nuts and see if the problem leaks go away. After a couple of startups on my rebuilt engine, several of the leaky nuts stopped leaking.

Then try a retorque of the leaking ones and if that does not work, what I did is to put some permatex aviation gasket goo non-hardening on both sides of the washer and when I retorqued them problem went away.

I have since retorqued them a couple fo times and no leaks

Dennis 69OTS

Agreed, I had the same problem after rebuilding the head.
After a couple of start/stop cycles, I tapped the A-corn on the side to make it slide on the head and hopefully seal up, I followed with a I re-torqued and problem solved.

I thought that the cylinder head nut torque increased to 58 ft lbs with the 4.2 engine and thicker head gasket as per the Service Manual Page B.X.s8.


for whats it’s worth I used the liquid aluminum version ( center pic ) with good results in my 69.


I used this, it had a great rating. So far itss working. Time will tell.

I agree with the other fellows who say it should go away after a cycle or two and re-torque

however, if you used new acorn nuts, I strongly suggest you check they are bottoming out with a.002 feeler gauge, had this situation, I noticed before job done and was subsequently advised re chrome old nuts is the way to go


What year car is this? I know on my ‘68 engine the stud holes are open to the water jacket. I had to put thread sealant on the head studs going into the block.

That is what I used in my Rover, with good results (as far as it could go).

It is a '69 SII 2+2, but… point to note is the block is from a '75 or after XJ6 as my original block was cracked but the head is original to the car. I’m told that these studs go right down to the bottom of the block and I put in all new studs.

I’m really hesitant to add any sort of radiator sealer on a freshly built motor I spent a lot of money on, and clogging up the internal water lines that reduces the flow. I guess if I have to I have to but… :slight_smile:

So far from what I have read, the suggestion of the new acorn nuts not seating all the way seems the most plausible, being a repro part and we all know about repro parts :slight_smile:

I appreciate all your help on this.

Retourqe the head every couple hundred miles until the torque stays at your prescribed setting
Mine took 3 times and now it is stays at 54 pounds foot.

I think the issue is that you want to stop the flow before it gets past the surface of the block and reaches the head and acorn nut. Putting a copper washer there even if it could work is a bandaid. Given the way things expand and contract with the temperature I suspect it likely wouldn’t even work. There is a reason the stud washers are extra thick steel.

Bar’s leak should hopefully seal the leak as it passes the stud. You just add it to your coolant and run the engine.

My block doesn’t have the long studs. I’ve never even seen one. Do they only have threads inside the block or is it threaded at the deck level as well?

They are threaded at the bottom, with just a hole in the deck that the stud passes though. There is a fair amount of space (a few thousands, not sure exactly how much, didn’t feel a need to measure last time I had the engine apart) between the stud and the hole in the top of the block. My studs were corroded all the way up, more so in the block than the head, but clearly I have coolant up there. There is a reason the long stud engine tends to have the head stick down. Anyway, not sure how easy it is going to be to get stop leak to work (also, somewhat opposed to using it on any machine I care about). Not sure why I’ve never had trouble with leaking there, but I do have my original washers and acorn nuts.

Wow that doesn’t sound like a great design. If there is any imperfection on the top of the head stud landing it’s going to weep. If I had one I think I’d use silicone or some other hardening sealant between stud and block hole.

That’s of course no help here unless the head is pulled. Maybe I spoke to soon and a thinnish copper washer under the steel washer could help, assuming it could stand up to the torque without splitting. Then Teflon sealant would need to go on the stud threads.

I have to agree, between the rotted studs and stuck head I think I would be happier with a short stud engine. With what POs used for coolant there was a mess in there, I’m hoping that a good, modern coolant designed for dissimilar materials will give less issue.