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I have an issue with the cylinder head on my 1985 series 3 XJ6. I had noticed some fluid collecting in the spark plug wells. I eventually realised that a core plug might be to blame. Having cleaned things up the two plug wells either side of a core plug had fluid in them. The fluid being coolant. The heat from the engine was evaporating off the fluid from the top of the block, leaving only what had run into the spark plug wells.

I thought this was going to be a simple case of replacing the core plug. I got a local mechanic to do this for me. He noticed that there was evidence of slight corrosion around the core plug hole and used some sealant to help with any possible leaks caused by corrosion. The core plug that came out looked as though some of the plating had come off. So I wonder if there was a bit of bi metal reaction going on there.

Sadly this did not resolve the issue so the exercise was repeated with a better sealant. Either JB Weld or something similar. This time, having completed the work and taken the car for a very short run, it was noted that a tiny drop of coolant was visible a couple of centimeters away from the core plug. Closer inspection suggests that there may be a pin prick size hole there. I have attached some pictures. Initial spot of coolant is at the top of the picture CP1. CP2 shows how this develops after about a mile or so more. CP3 after a mile or so more and after some of the resin has come away. Again some coolant can be seen but it's unclear as yet whether this came from the core plug or another hole.

You don't have to be particularly eagle eyed to see that there is obvious sign of a previous repair. This really only became apparent after I had cleaned off the residue of evaporated coolant. I'm wondering if this could just be a hole that was missed in the previous repair attempt?

I'm not really sure where to progress from here. I think the first job this weekend will be to run the engine with the vehicle stationary so I can witness exactly where the coolant is coming from. Will there be enough pressure in an unloaded engine to reproduce the leak though?

Is this a problem that anyone else has had? How have you resolved it?

I was wondering about drilling out the hole, tapping it and getting a small grub screw in there but am not sure if there is enough material in the head to avoid hitting a water channel.

I have been reading about vacuum impregnation for cast aluminum. Obviously this is a head off and strip down job. Huge expense for someone who is not up to this type of job himself.

Could any sort of welding be carried out insitu? Sounds risky to me.

I would much appreciate hearing of any others who have had similar experience and how they resolved or not as the case maybe.

I know it's a lot of work to remove the head but if it were me, I would want to understand whether the problem is indeed localised as per the pics or a warning about the general condition of the head. Certainly, any repairs would be easier with the head off the car. Mike.

Ian,

if it were me I would first try some Radweld and see if that works. (It worked on a cracked (in sevearl places) tractor engine block I had and lasted for quite a few years.)

The second option, if the hole is a pin prick is to drill and tap that and screw in a suitable screw with some thread sealant (loctite). Assuming the fault is between 1 to 3 mm in diameter then at least a10mm screw to eliminate posible minute cracks around the hole? Castings can prove troublesome to weld so I would try a mechanical solution at first.

Alec

Thank you both. Deep down I know the proper thing to do is remove the head but I’m still in the denial phase

If I do go down the drill and tap route what type of metal screw is safe to use. As I believe a steel screw would react with the aluminium in the head.

Hello Ian,

steel in aluminium will not be a problem, after all the plugs are steel bodied. Particularly if you use loctite on the thread.
personally I would try all ways rather than remove the head.

Alec

Sometimes the cause of the porous head is that previous owners may have not kept the correct coolant mix for the engine. That takes a while for an issue to arise. Most things can be repaired but it’s at cost unfortunately. The problem you have is coolant is exiting from the areas shown. You need to find where it’s entry is to properly fix the issue and that will require removing the head and a thorough strip down. The other way is buy a good replacement head. Rebuild that, then swap with the porous head.

I intensely dislike chemical solutions to mechanical problems, however, I would be inclined to instal K-seal in this case. Developed to cope with the design deficiencies of the Rover K series engine and cooling system, and really does a permanent job, contiuing to work even after subsequent coolant changes, yet does not coagulate to block radiator and heater cores.

Rob,

I disagree, how can removing the head show you anything as it is hollow. Porosity is a term used but I think that this is a casting fault, which has developed enough to start a small leak?

Alec

Rob,

I disagree, how can removing the head show you anything as it is hollow. Porosity is a term used but I think that this is a casting fault, which has developed enough to start a small leak?

Alec

Removing the head allows you to thoroughly determine the issue as it can be stripped and tested. Looking at a hole on the outside and sticking a bit of glue on isnt the best engineered solution.
You probably need to grind away the corroded area and see how deep the porosity is then possibly weld the area accordingly. So cylinder head off is the way forward for a perfect repair.