Overheating, mechanics can't find problem
 

Hey guys I have been re directed here from mini mania.

I have a 2005 JCW Mini Cooper s !

Randomly 6 weeks ago the car over heater and coolant started blowing out of the reservoir tank. I took it to a mechanic and he said it was the thermostat and housing and replaced those parts. I picked it up and it over heated again on way home.
Took the car to another mechanic who said it was the cooling fan so I had him replace that part and again it over heated on way home, so I returned the car to him and he replaced the water pump and reservoir cap, and again it over heated.
So now I have the car at another mechanic who has pressure tested the head and he says it all looks perfect, so he replaced the radiator and bled the car for 3 hours. However it still over heats for him.

The car over heats when you drive it and rev it up. It has been 6 weeks with no car and I have spent close to $3000. Can anyone suggest what it might be ?
Thank you

Could be a crack in the head, head gasket, air in the system, inoperable waterpump.

We have replaced two heads both of which on JCWs, due to a hairline crack in the head that is only visible when the valve cover is removed and engine has cooled down.

Find a better Euro specialist and have them do the diagnostic.

Crack develops around the head bolt on the back of the engine nearest the timing housing.
https://cimg3.ibsrv.net/gimg/www.nor...7c23022186.jpg

Sound fitting, would this not show in a pressure test ?
The car has been pressure tested 3 times and scores perfect.
Also the water pump is brand new.

The one car we diagnosed as needing the head replaced had been to the dealer 3 times prior, paid for the diagnostic 3 times over, not many shops know what they're looking for, especially dealers. They just hope the data leads them in the right direction.

You can also test the coolant for exhaust gas, which would indicate a failed head gasket/cracked head.

Remove the oil fill cap, is there a milky brown color to it? Pull the dipstick, color?

The one car that had a cracked head didn't leak enough coolant to change oil color, but wasn't able to hold pressure thus causing the overheat.

Oil colour is perfect and no exhaust emissions in the coolant. That has also been tested 3 times.

He is taking out the new water pump today to check it over, it's all too confusing to me.

Is it possible to have no water in oil and no gas and still have a crack in the head ?

If the leak is between the cooling system and lubrication system then yes, there would be no exhaust gases detected in the coolant.

Have them pull the valve cover and inspect the area pictured above. If everything else has been replaced and is working as it should there's only so many things that could be causing the overheat.

Have they done a compression AND leak down test? What were the results of either test, compression will be in PSI and leak down will be in %.

I will phone and ask for the results, thank you ! You have confirmed what I thought from the beginning that it is the head !

Leak down and compression test for sure. Hope its not the head , but looks like its pointing towards it. Post up if they pull the head and find the crack.

A cracked head normally shows up on when checking gasses in the coolant or visible in in the oil. However, since you have eliminated all the other potential cause, it is directing more towards this. I take it the cooling fan is fully operational? I would have that waterpump checked again.

Where this crack develops is not into the combustion chamber, it is from the water jacket into the crank case, no combustion gasses will be evident.

We've had one customer recently that had a failed HG between 3 & 4 who had the same problems of overheating and coolant out the expansion tank.

As long as the PTO gears are spinning in the SC, the water pump is working. Very simplistic system.

Unfortunately you need to either find another shop to do the diagnostic, or go on a whim and have the head pulled, dye tested, gone through, HG replaced. In these temperatures you won't have an overheating problem if the fans aren't properly operational.

Yes, understand what you are saying but often the waterpump may be spinning but the impeller may not as come loose from the shaft. Although I do appreciate that the waterpump has been changed. Would a hairline crack between the water ways and oil gallery or crankcase show evidence in the coolant? over time should he not see a rise in oil level from the leaking coolant? Also he shouldn't eliminate head gasket.