Hi all, I have a 2015 1.6 TDCi Estate. Five months ago the heater was blowing hot air, then suddenly went to cold air. I then started noticing the car would heat up very quickly, blowing out hot after driving for 1 min, the temperature gauge would go up quick, when it got to the middle of the gauge, 90 degrees, and I assume when the thermostat opened, the needle would drop down to the bottom of the gauge and make its way back up again. It then stays at the middle, never overheats and runs fine. I then noticed the water in the expansion tank would go from maxi to minimum when hot and back up to maxi when cold. Garage couldn’t find anything wrong. I changed the thermostat, no difference. The bleed nipple on thermostat if unscrewed takes 15 sec for fluid to appear. The new thermostat split in half 10 weeks after it was changed, I assume because there were periods when no water was in it. I have changed it again, since then, 8 weeks, have put 4 litres of coolant in topping up expansion tank. I can’t  see any leaks. I have replaced expansion tank cap. The oil filler cap is fine no white gunk and no oil in expansion tank. Please help 

i have read somewhere that if there is no obvious leak on the outside then the leak might be in the engine such as going down the cylinder through the exhaust pipe or mixing with your oil.

have you checked the oil cap for any white substances? or is your exhaust blowing white smokes?

edit: sorry only just read your last pipe regarding your oil.

have a check on the exhaust pipe when idling.

Thanks froggy8 I will have a look when idling, but I haven’t noticed any white smoke, just going to have a look

I don’t know why the temperature gauge goes down when the thermostat opens, is that an air lock somewhere?🤷‍♂️

from what i have read, the thermostat opens to let cold water in the engine so i think it is meant to drop the temp abit.

No white smoke. But did notice oil in the middle of the black thing under the expansion tank. Don’t know what it is

3 minutes ago, K9s said:

No white smoke. But did notice oil in the middle of the black thing under the expansion tank. Don’t know what it is

i have just made a thread about my leak few days ago, mine was leaking at the very same spot as yours if that 'oil' is coolant.

i just changed my tank yesterday as i had a tiny crack and it was leaking on that round thing same as you.

look under the tank and see if its wet.

this is what happened to mine:

 

 

Tank is dry, don’t know what this black thing is, I thought it was an engine mount

1 minute ago, K9s said:

Tank is dry, don’t know what this black thing is, I thought it was an engine mount

i dont know what it is either.

Run car to normal operating temperature looking for leaks, had heating on hot and full blower, air coming out is cold🤷🏻‍♂️

Water in expansion tank has now dropped to below minimum and heating is now hot

1 hour ago, K9s said:

No white smoke. But did notice oil in the middle of the black thing under the expansion tank. Don’t know what it is

That engine mount is hydraulic.  There's oil inside it to smooth out engine vibrations.  Once the oil leaks out, it can't be repaired, just needs replacing.

Thank you, something else to sort out 😮‍💨

7 hours ago, K9s said:

Hi all, I have a 2015 1.6 TDCi Estate. Five months ago the heater was blowing hot air, then suddenly went to cold air. I then started noticing the car would heat up very quickly, blowing out hot after driving for 1 min, the temperature gauge would go up quick, when it got to the middle of the gauge, 90 degrees, and I assume when the thermostat opened, the needle would drop down to the bottom of the gauge and make its way back up again. It then stays at the middle, never overheats and runs fine. I then noticed the water in the expansion tank would go from maxi to minimum when hot and back up to maxi when cold. Garage couldn’t find anything wrong. I changed the thermostat, no difference. The bleed nipple on thermostat if unscrewed takes 15 sec for fluid to appear. The new thermostat split in half 10 weeks after it was changed, I assume because there were periods when no water was in it. I have changed it again, since then, 8 weeks, have put 4 litres of coolant in topping up expansion tank. I can’t  see any leaks. I have replaced expansion tank cap. The oil filler cap is fine no white gunk and no oil in expansion tank. Please help 

Any ideas anyone?

there is a cheap kit you can buy to test the coolant if that helps.

Have you checked for leaks inside the cabin?

If the heater matrix is leaking, the coolant could be under the carpet.

16 hours ago, K9s said:

Water in expansion tank has now dropped to below minimum and heating is now hot

The simple answer there is air in the system.  

I can't say where it's coming from at the moment.  But I suspect it was never bled properly in the first place.  Some cars are just awkward to bleed.  I wonder if it's worth having the system vacuum filled as it should be?  Vacuum filling means there can't possibly be any air left in the system.  Indy garages are unlikely to be able to do it, but most main dealers should have the equipment.

You can have a sniffer test done to check for hydrocarbons in the coolant, which would indicate a faulty headgasket or EGR cooler, allowing exhast into coolant and vice versa, but I don't believe that is the issue in this case.

Thanks guys for your comments, it’s appreciated. I did check inside the car for wet, didn’t check under the carpets, but had a good feel around and it’s dry. 
 

I was thinking of booking it in to a main dealer and getting their opinion. 
 

thank you again