Quick update
Hi all, quick update!
I took the car into Vauxhall garage to get them to look at the thermostat. They couldnt find any leakages from the thermostat or the surrounding housing. They did a pressure test, and called me to tell me that they think there are no leaks, and everything seems fine, but that the presence of some coolant residue on are area of the engine near the water pump (ON THE OTHER SIDE OF THE ENGINE FROM THERMOSTAT) sugegsts that there may be a small leak form the water pump. The told me they suggested replacing a seal. £53 they quoted me. I told them that the water pump was on the opposite side of the engine to where coolant was pooling on the driveway so i didnt see why i should replace a seal for a leak which hasnt ever presented itself to me. the only evidence they were going by was the residue on the waterpump area. I obviously refused the sugestion to replace the seal. Vauxhall were useless. so i picked up the car and have taken matters into my own hands.
I looked again at the thermostat housing. i ahve identified that: the leak only happens overnight or when the engine is completely cold. the leak is coming from either, the sealbetween the thermostat and the thermostat housing, OR from the seal between the pipe exiting the engine block coolant jacket which also joins onto the thermostat hosuing. one is above the other and so it was difficult to identify specifically which one was leaking.
Regarding the point about the leak only happening when engine is cold: This suggests that when the engine is hot, the expansion of metal and plastic parts is enough to plug any gaps. its only when the engine is completely cold, and when these parts are compeltely contracted that the leak is occurring. To me, then lead me to suspect that the first line of enquiry should eb to check that all the BOLTS surrounding the thermostat/housing seal AND the coolant jacket/thermostat housing seal are propoerly tightened. so out came the torque wrench today whilst it was still daylight.
I started by checking the bolts around the thermostat housing/thermostat. lo and behold, the lower right bolt holding the thermostat into the hosuing was very loose. i was able to loosen it with my fingers! I didnt have the factory torque settings to hand by i tightened the bottom two bolts on the thermostat housing to a tourque of 10nm which to me is a default torque setting which is much more than finger tight, but not tight enough to cause any problems (i hope). the top right bolt was not reachable so i didnt tighten this one but it seemed to be tight enough already.
I also tightened the two boths on the seal between the pipe of the coolant jacket where it joins the thermostat housing. these were also a bit loose if you ask me- certianly less than 10nm torque so tightened these too.
lastly, i topped up the coolant, and checked that everything was dry. I will see tomorrow morning if there are any signs of leakage. I hope the above tightening will have solved the problem, becaus ei cannot see any signs of cracking, or other damage on the thermostat housing, and these loose screws seem to make sense as being the cause of the slow leak i ahve been experiencing.
ill keep you updated.
PS you can see a photo of the thermostat housing and the location fot he screws i tightened below. i found this picture online. it is the mokka thermostat hosuing and shows the location of the screws i tightened. (gold/brass coloured sockets) the two at the bottom of thelarger opening were the loosest screws on my mokka!...
fingers crossed its all sorted now.