sepulchrave

It'll be just fine for topping up, oil doesn't separate into anything, it stays as oil for millions of years before we dig it out of the ground.

Injectors, 1.6 TDI eats them for breakfast and they're expensive, these cars often end up on the market once injector faults start to appear because you have to change the whole lot for a new set.

The turbo is a mechanical device, only the actuator is electrically operated. Have you checked that the wastegate isn't actually jammed since this would give the same symptoms but the ECU would be unable to tell you about it. Which scan tool are you using?

Due to the age of the vehicle I'd be amazed if it was the original turbo.

Has the turbo ever been replaced?

If there's no signs of any damage and especially no sign of oil contamination then the belt will be fine, the reason is that the cambelt has very light duty due to the roller rocker valve gear putting very little stress on it. I've not heard of a cambelt failure on any 1.4 petrol engine in all the years I've been here. You'll be fine.

You're right about the wheels, I was thinking of 15's Vs 16's. Knock yourself out, no-one else has fitted Mark 1 312's to a Mark 2, you'll be the first. I thought all the bits were the same so how exactly would it need different brake lines?

If the brakes fit, the lines should fit, obviously the car needs to be on 17" rims or bigger as well.

Unless you have symptoms of fuel starvation changing the petrol filter is a total waste of time and money.

You'll need to do more than just 'turn' the cap, you'll need keep loosening it until there's a pop of pressure or the cap comes completely off. If you get a pop, immediately screw it back on to avoid the coolant boiling.

I suspect you're overthinking this somewhat. The most likely explanation that rev N is not recommended for earlier cars is that it simply hasn't been tried with them.

No coolant pressure when the engine is still hot after a run?

Ah cannae change the laws of physics captain...

Ok, I give up, it's a petrol engine, it's not a Jaguar XFS, give us a clue...

No, because you'll be fitting all the sensors and ancillaries from your old engine so there won't be any difference from the ECU's point of view.

Head lift is NOT the same as a failed head gasket, the coolant is pressurised by combustion gases ONLY under full boost conditions, even when the coolant is cool this pressure remains in the cooling system, during the head lift the gas pressure pushes coolant out of the pressure release valve which is in the expansion tank cap, hence the cap becomes loosened by the coolant blowing past it.

You may have head lift, does the tank release any pressure when cooled down?

No, you can do that, the clutch will just slip as soon as you get on boost and the standard intercooler will heatsoak almost immediately so power will just drop like a stone. Pointless really.

The 1990's called and wanted their throttle cable back...

If you want 200 horse you're gonna need a new turbo, intercooler, hard pipe kit, and a new clutch, slave and flywheel, the remap is the cheapest bit by miles! You're not thinking straight, think like your bank manager, not a wannabe racing driver! For 165 horse it's £300, for the rest it's more like three grand and that's assuming you can do most of the work yourself!

Somewhat passed sad and heading towards sentimental!

Just remap it, that'll give you enough without ruining it, go for a low torque remap to spare the clutch and flywheel.

Battery no good.

Yes, I've been here a very long time, back in the PD's hey day injector loom failure was common, injector failure, very rare. So...

More likely to be the injector loom than the injector itself, also a much easier and cheaper repair. Always ask first, it's almost never the part mentioned in the diagnostic trouble code.