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Dubya · 23rd October 2019, 09:11

A couple of years ago my thermostat cracked catastrophically, managed to get the car home eventually (many stops to let it cool down) with no overheating damage. I fitted a full thermostat kit from Matt, bled using the approved procedure. No issues afterwards, heaters warm, no coolant loss. However the normal running temperature fluctuated between 81 and 84 degrees, no-where near 96 degrees as been suggested is the norm. As said I have had no issues...until recently! Coolant level low, topped up but evidence of leakage from the expansion bottle cap. A couple of days later while sat in traffic I saw steam from under the bonnet, checked OBD and temperature was at 107 degrees before the fan kicked in.

Further investigation found the fan low speed was kaputt, and the high speed kicked in just as the expansion bottle cap would let go, also coolant in the 'vee' due to a hole in the straight pipe between the pump and the thermostat.

I have ordered another thermostat kit from Matt, along with a gold resistor to restore fan low speed operation, when fitted I will report back regarding the running temperature and see how it compares.

Edit: The expansion tank cap has 140 on the top, is this the temperature at which it opens? If so would it be wise to replace this too, seeing as it is opening at 107 degrees, or could the pressure at this temperature have been sufficient to open it?

23rd October 2019, 09:11	#10
Dubya Loves to post 2005 MG ZT-T+ V6 190 Join Date: Jun 2015 Location: Hereford Posts: 474 Thanks: 126 Thanked 139 Times in 103 Posts	A couple of years ago my thermostat cracked catastrophically, managed to get the car home eventually (many stops to let it cool down) with no overheating damage. I fitted a full thermostat kit from Matt, bled using the approved procedure. No issues afterwards, heaters warm, no coolant loss. However the normal running temperature fluctuated between 81 and 84 degrees, no-where near 96 degrees as been suggested is the norm. As said I have had no issues...until recently! Coolant level low, topped up but evidence of leakage from the expansion bottle cap. A couple of days later while sat in traffic I saw steam from under the bonnet, checked OBD and temperature was at 107 degrees before the fan kicked in. Further investigation found the fan low speed was kaputt, and the high speed kicked in just as the expansion bottle cap would let go, also coolant in the 'vee' due to a hole in the straight pipe between the pump and the thermostat. I have ordered another thermostat kit from Matt, along with a gold resistor to restore fan low speed operation, when fitted I will report back regarding the running temperature and see how it compares. Edit: The expansion tank cap has 140 on the top, is this the temperature at which it opens? If so would it be wise to replace this too, seeing as it is opening at 107 degrees, or could the pressure at this temperature have been sufficient to open it? __________________ 7,925th ZT-T to run off the production line, out of 8,249 The 1,709th ZT-T 190 + to be made out of 1,756 The 103rd ZT-T in Mica Blue (Ignition) (code: JGY) to be made out of 160 Mica Blue (Ignition) ZT-Ts Last edited by Dubya; 23rd October 2019 at 09:14.. Reason: Added expansion cap question.