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Leaky thread

The oil pressure sensor is a unit that is basically a bolt (with an electrical connection at the end) that screws into the side of the engine block. And it's leaking oil. :-)

Now, it wasn't flush with the engine block - there's maybe 5 mm of thread (out of 10 mm total) protruding. So I unbolted it, cleaned up the manky stuff on the threads and around the hole, and bolted it back to the recommended torque. There was even more thread showing than before.... but I turned the engine on and it started spewing oil at quite an alarming rate.

So, out it came again, and this time I cleaned out the inside of the hole as gently as I could with a small screwdriver. There is a lot of clag in there, but not knowing quite what was on the other side, I didn't want to start gouging pistons or thread. So, back it went, and this time I crossed my fingers and tightened to about 25% over torque. (I know, I know). Now only about 4 mm of thread showing. But, Ahah! No leakage.

For two weeks. And now it's back with a vengeance. So, out it comes again (which is not so simple - have to borrow the neighbour's inspection pit, remove the oil filter...), clean it up, and try some high temperature gasket compound before screwing back to 25% over torque. No joy. Drip, drip, drip. I didn't really expect the compound to work, because it wasn't being compressed...

So, any ideas? Before I limp to a garage? I suspect the inner oil paths are full of crap - it's a Ford HCS engine which is renowned for this - and I suspect the crap is stopping the bolt screwing in fully. But I'm loath to put in a tap to clear out the thread, not knowing what's on the other side, or to squirt in anything to clear it. I'm thinking maybe a steam clean of the whole oil system is the way ahead - how much is that likely to set me back?

Thanks in advance, Rich.

Reply to
richard
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Have you tried PTFE on the threads?

Reply to
SimonJ

If the switch itself isn't cracked or leaking, then I would suspect that the boss in the engine block is cracked. This is very difficult to fix.

mrcheerful

Reply to
mrcheerful

Loctite 569, 577, or 542 hydraulic sealant. Any of those should do the job.

10 ml bottle around £5. Obtainable from industrial small tool suppliers. Buck & Hickman, J&L Industrial Supply etc. Anaerobic and will seal high pressure unions even if only hand tightened. I've actually sealed loose unions with it when I've wanted an elbow, whatever, to point in a particular direction. Clean the threads and well coat the sensor thread. Screw in as normal. Leave for an hour or two (I think) and it should be sealed. Mike.
Reply to
Mike G

Rich,

I imagine it will set you back the cost of a new engine.

Check the thread on the switch, if it is damaged renew the switch. You will not damage pistons etc. by cleaning out the thread in the block. If you decide to clean out the thread with a tap be carefull, this may be a tapered thread, probably something like 1/8 NPST. It is correct that the switch does not screw fully home, this is because, see above, that the block, switch or both have a tapered thread. I suggest replace the switch, clean the thread in the block and fit the switch dry.

S
Reply to
Steve M

It works best if you clean the oil off first, brake cleaners good for this :-)

Reply to
DuncanWood

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