Blown head gasket?

My 300Tdi truck cab Defender has developed a squeak! It only happens under acceleration. I dug out my compression tester then realised there wasn't a spark plug hole to stick it in! I removed the fan belt and it still squeaks so it isn't any of the ancillaries. There is an oily patch on the block just below the head. Is the 300Tdi head gasket known to be a weakness?

No spark plug hole on a diesel - but there is a glowplug hole you could try instead

might be your throttle cable needs oiling

I assumed the glow plug hole would be too small but I'll have a look anyway.

You may need an adaptor, however, glowplug hole is the standard for compression checking on a diesel.

From what I've read on other forums it sounds like it might just be the inlet/exhaust gasket. Aparently they commonly fail on number one cylinder.

And you will need a special diesel gauge when measuring the compression. At best, a 300tdi will give 24 bar max, which is ~350psi. Don't try it with a petrol engine gauge!

My gauge only goes up to 300 psi. Anyway, I have convinced myself that the problem is simply a blown inlet/exhaust gasket. I hope I'm right!

yeah, sounds about right there for a 300tdi

The squeak is cured! I replaced the manifold gasket and it was still there. While doing that I noticed black gunge inside the inlet manifold so I suspected a turbo problem. Meanwhile I investigated a vibration which turned out to be a knackered universal joint. I replaced the joint and guess what? No squeak! Strange that it only squeaked at certain speeds in each gear, it seemed to be related to engine speed not road speed. As for the turbo, I'll worry about that later.