NCT: Car now undriveable

You signed a waiver to have your car tested so you will have no comeback with the NCT. It sounds like your engine was already on it's way out so it would have happened eventually, test or no test.

Compensation for what?

Your car clearly had a fault going in.

5. The engine is in a fit state to be tested e.g. cam belt / timing belt. You may be asked to sign a disclaimer at the test centre. 

Taken from the FAQ on NCT.IE

Edit: From your OP was it the the tester "mechanic" that said the engine wasn't fit state to to be tested and because of that didn't?

I have always been asked to sign a disclaimer for diesel cars and never for a petrol car.

In any event I doubt that you will get any compensation your engine was either on the way out or required repair before it did fail nothing to do with the test.

"The mechanic told me he didn't do the emissions test because he thought the engine might explode (his words)"

This tells you all you need to know. He didn't even test it as it was so dangerous. Of course you are not entitled to compensation. Maybe he's entitled to compensation from you for bringing in a car that was so dangerous to potentially cause him harm if he tested it.

If the NCT test is going to cause a problem to arise, then that problem was going to arise anyway.

Better that it does arise in the NCT centre than when trying to make a manoeuver at 120KM on the motorway!

I know at the NCT centre in Ballymun whenever I've been there, when the lads collect the cars from where the customer parked it, they usually give it some beans on the way around to the entrance to the test area. (In my opinion this is perfectly fine as it'll give them a bit of a feel for the car before testing it). So am wondering if the OP was essentially nursing the car (as it already had a pre-existing rattle), and when the NCT guy jumped in, simply drove it like any car would be driven and that perhaps exacerbated an already pre-existing condition?

+1 on checking the oil, if you did and topped it up did you replace the oil cap afterwards?

When I had the NCT a few months ago and was collecting the keys from the counter another customer was doing similar to be told the engine was knocking, car was low on oil and that the engine bay was covered in it. Turned out the lad had topped up the oil the day prior and forgot to replace the cap making a proper mess of everything.

Ah now, they also shake it a bit to test the suspension, and brakes... could easily have dislodged some of the Sellotape or Velcro that was holding the exhaust and engine bearings together

Did this rattle, by any chance, sound like a small person was inside the crankcase, hammering to get out? Does it get faster when the engine spins faster? Does it get louder when the engine's under load.

Something like this:

https://www.youtube.com/watch?v=CyxTNuW4apo&t=160s

If you keep driving that thing it'll give itself a new inspection window in the block soon enough.

It needs new engine.

Step 5 of the NCT pre-test checklist would apply here.

Once warmed up a healthy engine should run normally through the full rev range up to redline.

They aren’t liable if your engine fails as they drive it in to, or during, the test. Catching potential failures is the job of your local garage / yourself. I’d say this is just a case of bad timing really, it was going to fail - NCT or not.

Very hard to believe this is not a wind-up.

OP - besides all of the valid points raised, if they were to give you anything it would set a crazy precedent.

They'd have every "close to death" car in the country brought in

What did the garage that collected the car say was the issue?

Would think it very unlightly the NCT will entertain your compensation request, as you did successfully drive it away from there yourself.

What make model year and milage is on it?