Mini Cooper Overheating

[Lemond]

Is it possible for air locks in the coolant to cause the engine to overheat. Williams Bolton claim this happened during a service on my cooper today. They have retained it overnight to "check it"

[pisquano]

could it be the reason why my mini seldom shows mild signs of overheating?
how long could an airlock last in the tank before it's "naturally" expelled?

my coolant has been refilled from 0 more than 2 months ago now

[C.Noble]

Air locks will cause over heating, but an air lock can only be present if someone never bled it right in the first place... did they change the coolant as part of the service?? or the coolant level has been allowed to drop too low, in which case where did it go?

Common causes for leaks are radiators, thermostat housings split/distorted and cracked expansion bottles (MCS only)

It is possible however that the coolant has been lost over time as it has experienced short "overheats", this is quite possible as the guage doesnt show overheating until its REALLY hot! (see this link for guage operation http://www.mini2.com/forum/first-gen...ml#post3724708 )

Possible causes of overheating (usually when stuck in traffic) are stuck thermostat, bad connection at fan motor, bad connection (for fan motor) in multi connector (clips onto airbox) and I have seen one faulty Engine Coolant Temperature sensor that was reading wrong, but not wrong enough to "flag" up a fault in the engine ECU.

If your car is a Cooper (not an S) get whoever is looking at your car, to check the pressure cap seal's condition. I had one car a couple of weeks ago that had this seal perished causing the cooling system to NOT pressurize, that combined with a low antifreeze content in the coolant caused the system to boil up just BEFORE the fan cut in (spewing out a little coolant everytime) the reason for the boil up is that the fan should cut in at 105 DegC, which is fine for coolant pressurised to 1.1 bar, but is over boiling temperature of coolant at atmospheric pressure.

Hope this helps.

[Lemond]

The coolant strength was weak 15 months after williams manchester changed it. This was highlighted in an inpection 2 service. They changed the fluid but after calling us to tell us the car could be picked up ...they called back to say during a road test the temp had risen to much and the system needed bleeding...hmmm. They claim that they stopped the car and allowed it to cool down.... I am not so sure. As it was back in the garage 10 mins later. They asked us to leave it overnight so they could check it in the morning. This was all at Williams Bolton. I am not happy. Never had a car serviced where they botched the coolant change and am unsure if they could have damaged the cylinder block by driving it while overheated.

[C.Noble]

Pretty bad if they botched a coolant change... a bit of a rookie error that one, but it does sound like that is what has happened.

It is unlikely they have damaged the block unless it was REALLY hot, but depending on how far they drove it overheating, there is a good chance the head has been warped and the head gasket blown... all depends on how vigilant the mechanic was on the road test.