I'd say whip the belt cover off and check the water pump.

Would the steam be that noticable?

I've check the inside and all is dry. Heater is working fine too.

Checked under the car and cant find any wet spots or puddles. I am totally stumped.

No white smoke at all either.

I am sure you would notice any steam coming out of the bonnet whilst your driving, check inside the car incase the heater matrix is leaking, look for any wet spots, it could be leaking anywhere, check all coolant pipes and the rad, thermstat housing, water pump etc...
No white smoke at all out of the exhaust mate?

I recently picked up a Corsa C 1.3CDTI for my girlfriend. I serviced it and replaced the drive belt (not timing belt) as it was making a horrible grinding noise but is fine now.

The car is running fine, no blue smoke out the back and no “mayo” on oil cap or dipstick so i doubt it is the head gasket.

The other day I noticed the heater was cold and the water temperature was high so I checked the coolant and it was low. I topped it up and the heater and water temperature returned to normal.

The coolant is still going down fairly quickly though. I cant find any leaks.

After a 20 mile journey today i took the cap off the header tank and the was no pressure. I was expecting a ‘Ssssshhhhh’ noise when taking the cap off??

The question is where is all the coolant going and why is there no/low pressure in the system?

Is it possibly the header tank cap is not sealed and its escaping in steam??

Thanks for any pointers in the right direction :thumbs: