error code says cylinder 8 misfire, cylinder 8 spark plug is very wet but can't tell if that is coolant or gasoline or oil, can I borrow engine compression tester from AutoZone to find out if headgasket leaks? what is 2000 Discovery cylinder compression (PSI)? thanks.

or, any other way to find out if headgasket need to be replaced?

 

why the assumption that it may be a headgasket issue?

Check the ceramic part of the plug for cracks and also the plug wire. It could be a bad plug or wire and not arcing in the combustion chamber. If the plug is not firing, your plug will be wet... from unburned gasoline. Check the simple things first.

 

The head gasket is quite thin (way too thin IMHO) on that cylinder where the water jacket channel runs by. It can fail into the cylinder or external down the block or both. Can have overheating, exhaust gas bubbles in coolant (the under dash gurgle that won't go away), misfires, white smoke out tail pipe that continues. But agreed you should check the simple plu issues first. There is also a green dye that can be put in coolant and it will show up as flecks of it on the spark plug if you have a leak. You can also buy a chemical test for around $50 at parts store that tests the coolant and changes color if HG is leaking exhaust into coolant - does maybe 15 tests. Here's pix of blown out HG on a rear cylinder.

 

So when was your engine last tuned along with new 8 mm silicone wires?????
If you have the old grey plug wires, it is time for a tuneup cause they are failing on you which will cause a misfire.

 

I bought this Disco at 150K I think plug wires are old, how do you test these old grey plug wires? thanks!

And, do I need to remove intake manifold when changing plug wires? thanks again.

 

Buy a set of STI wires from British Parts of Utah and some plugs from your local parts store, might want to try some E3-48's, they work well in your engine.
As for installing the wires, I can walk you thru installing the wires without pulling the manifold when you get ready.

 

before I buy new wires how do I test my old grey plug wires?

is Mallory Sprint Wire Spark Plug Wires (8mm) good enough?

many thanks

 

ohmygoodness,, coolant expansion tank becomes so hot you can see boiling coolant running inside coolant tank, and about 20 minutes coolant levels drop to nearly empty, I let engine cool down and open coolant tank cap and coolant return to the tank about 3/4! where is the other 1/4 coolant go? blown head gasket?! but I don't see white smoke from exhaust, I don't see milky oil on the oil stick?!

I noticed coolant dripping from around crankshaft front pulley!? really?! how can it be possible coolant running out from the crankshaft front pulley??! should be engine oil not coolant, right?! can anyone help? I have replaced crankshaft front seal, water pump, thermal stat, upper radiator hose with bleeding screw, power steering pump, etc.

 

The coolant level dropping and returning - sure sign of head gasket problems.

Mine did the same thing.
Plus the cylinder #8 is a dead giveaway.

On these engines - head gaskets wear out like shoes.

So, get a new pair of head gaskets.
Do BOTH heads now.

You'll smile when it is over as you'll have a new engine experience with NO problems.

Ignore it and you'll probably blow a hose from pressure or over heat the engine.

Think of it this way...
Head gaskets being bad is a "good thing". At least you dodged the slipped liner problem.

Your problem is correctable.

 

thanks for advise, I have a compression test tool I want to test compression rate in cylinder 8, what is cylinder 8 compression psi?

thanks again