Coolant pushing past expansion cap not head gasket

Hi All

We are at end of our tether, and on the verge of scrapping our 3.0dci V6 Grand Espace. We have had it six months and it has been in and out of the garage, luckily for 3 moths of those it was under warranty.

Started with check injection and going into limp mode. God knows what the garage did to it, but sure no more check injection. Then noticed a coolant leak, hose had gone, replaced it, now coolant overpressurises into the expansion bottle, comes through seal, ****es all over everything.

Has been into renault dealer, they bled the system, drove great for a day, then under load, old probs are back.

Renault had it back in, have now decided that they cant possibly ascertain where the air may be coming from (head gasket dye test proves Negative)

And as its a V6 gthey wont touch it as it is just too much work to make it economically viable (121000 miles and 2006 model)

Sooooooo, engine runs fine, sounds great, deffo loss of pwer (i think, but then im driving it V carefully)

FAR too good to scrap, cant help feeling we could be trying something else,

ANY advice appreciated, keep it coming :)

Thanks