I would cut the plastic housing with a hacksaw around the bolt area to expose the bolt and then using some mole grips (self locking pliers to remove the bolts).The only other option is to remove the housing ,do as above then apply some heat from a blow lamp to the bolts. obviously you couldnt do this when its still bolted to the engine.

 

Thanks for that. That's the way I'm leaning but I wonder about option 2. Remove the whole assembly from the engine block.

Can anyone clarify if there is also oil passing through that bit and if there would be any special challenges on removal and refitting.

 

If its at the front of the engine ,no oil passes through the housing.If removing the housing you will need some gasket sealer to reseal the housing.

 

Ah, good.

You mean hylomar?

 

Thats the stuff!:d

 

HUZZAH!

Thanks. That's next Sunday sorted :d

 

Various methods for getting stuck screws out.
Use next size up torx head and tap into chewed hole, turning to undo as you do.
Use small chisel on outside of head to tap it loose
Drill or grind head off then after housing off, use mole grips on remaining stub.
Drill in and use extractor
Hacksaw across head and use flat head screwdriver

Good luck

 

One other method depending on access which may / may not work is an Impact Driver with a well chosen bit. Have to use with care though if cast brackets are involved... snap ​

 

Thanks Dancingdad and Renoir.

The trouble with most of these solutions is access. I don't think the impact tool is a runner.

I like the idea of the next size up torx bit but I'm not sure if there's enough room to get a decent swing with a hammer.

Screw extractor sounds interesting. The extractor bits are cheap enough but I wonder if there is room to get in to drill the pilot hole.

I had thought of cutting a slot in the head and I think there's enough room to do it.

Thanks again all for the suggestions. I shall report back.

 

.......I like the idea of the next size up torx bit but I'm not sure if there's enough room to get a decent swing with a hammer..........

You don't actually need a decent swing. Light taps and turn the driver, you don't need to go incredible hulk on it, just pressure and impact can often break the lock and start them turning.

Similar with the small chisel or centre punch on outside of the head. Sorta 45 degree angle anticlock and off vertical, gentle taps and sometimes amazing results

You can also get drill extractors. Sort of a reverse drill bit with no flutes. Drills in backwards and grabs, unscrewing the little swine. The ones I've tried seem okay on wood screws as long as you wind the torque down on the driver, too much and they drill in and strip.

With any tight screws, rather then bags of torque unscrewing and risk stripping the drive faces.
Tighten and a few taps at the same time can often release the grip and won't damage the unscrewing faces.

And penetrting oil :d

 

Cheers, more things to try.

I shall overcome.