Right. Fitted new oil cooler yesterday. Was idling fine, no leaks, gave it a quick run round the block to test, was fine.
Later, took it to the shops and I could hear it boiling away. Pulled over, popped the bonnet, coolant cap was doing a geyser impression, but I could hear bubbling coming from under the plenum. "Oh bother" says I, limps it to civilisation (low coolant warning came on) and called the RAC. Towed home, and just pulled the plenum etc off, expecting to see evidence of the plate leaking.
Dry as a bone - slight trickle from the drivers side bolt on the coolant bridge, so I'm thinking I've not fitted the washer correctly.
Now, I suspected previously that the coolant pressure cap was faulty - there was splattering of coolant behind it.
If it was faulty, could it be that its let air in, so boiling the fluid and forcing it out through that tiny leak?
Obviously I've refitted the washer, there was no sign of actual damage to it - and intend to use my known good radiator cap off the dead 2.6.
Finally (sorry, I'm thinking as I type) - can I refill the cooling system and turn the engine over by hand, and see if there is a leak on the coolant bridge bolt, or indeed anywhere else?