1.8T Coolant Leak
 

When left unused for a week or so my MkII 1.8T loses a lot of coolant.


The system has been pressure tested, and the engine left running for 1.5 hours, but no obvious leaks have been identified.


Can anyone suggest where I should check to try & find the leak?

The metal coolant pipe that runs around the back of the block has been known to leak around the mounting brackets, not always obvious as the leak tends to evaporate as it runs down the block.

When cold, try running your hand along the rear of the block, below the inlet manifold, sometimes the coolant will be present there from the IMG. When hot it the metal expands and does not leak.

Check all the hoses - I've seen a spate of failures recently, some of which are right next to hose clamps.
You can get a full set of 1.8T hoses for a relatively low price (compared to the individual prices) here:
https://www.dmgrs.co.uk/products/rov...inc-thermostat

Good luck, intermittent leaks can be a real pain to find.
Also, check the cambelt side of the engine for leaks towards the bottom - indicative of a leaking waterpump.

Good luck!

In addition to what the others have said. If there are no visible leaks or dried in coolant staining to be found perhaps the coolant is leaking into the sump. This can occur if the elastomer bead in the head gasket has lost its bond on the gasket (or a crappy fitted MLS gasket could be culprit) allowing coolant to enter the oil drain and then to the sump.

Is the oil level increasing over time? The coolant will sit in the lowermost part of the sump below the oil and will be unseen until it fills up enough and starts to enter the oil pump suction pipe and then the mayonnaise circle of destruction begins with contaminated oil wearing the turbo bearings, mains and big end bearings, camshaft bearing surfaces.

I would look for a small puddle under the water pump. Leaks when stationery and stops leaking when the engine warms up. Starts to leak a few hours after the car has stopped when it all cools down. I’ve had 2 k series engines do the same.