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Hi, I'm new here and I really need all and any advice I can get for my 2011 Manual 1.4 Ford Fiesta Duratec (Malaysia) that has been running on a high coolant temp but isn't overheating for the past 2 months. I'll list down what I've changed below and also elaborate more on the things I've noticed...

Parts changed :
1. Radiator
2. Coolant temp sensor
3. Thermostat housing upper & lower
4. Thermostat
5. Coolant reservoir tank

* I've got an OBD display therefore I can tell the normal coolant operating temp for my Fiesta. With the AC off my car would be running at between 89 c° to 95 c° on a normal day (38 c° outside temp in South East Asia). And with the AC on, the coolant temp would be between 91 c° to 94 c° (38 c° outside temp).

About a month and half ago, my coolant temp suddenly went up to 108 c° while driving slowly at a commercial area looking for a parking bay. The radiator fan kicked in at 105 c° as it should but the temp wasn't coming down so I parked and switched the engine off (fan continues running with ignition off till temp drops to 99 c°)

Ever since that day, I've sent my car to 5 or 6 different mechanics with 1 of them (mechanic 1) saying I've gota blown head gasket, 1 (mechanic 2) saying my cooling system is air locked and the remaining ones are clueless. Mechanic 1 replaced all the above parts except the radiator and reservoir tank. After all the replacements the symptoms are the exact same as before changing.
Mechanic 2 bleed my cooling system and the the problem was gone except for the temp being slightly higher than normal at 96 c° with AC on. I saw that the coolant level was above the max line so I removed coolant till the mid way point between min and max and my Fiesta was running perfect with AC on the temp is stable at 93 c° and AC off at 95 c°. It was this way for 3 days straight till I replaced the coolant reservoir tank (by myself). And Ever since I've replaced the reservoir tank, the temp has again gone back to running high (95c° to 105c° sometimes slightly higher at 105 but will go back down to 99c° when the fan kicks in). I've also tried bleeding my cooling system numerous times but to no avail (I'm not a mechanic, just a guy that know a little about cars). And from all the times I've tried, I've always noticed that the bloody thermostat always remains closed therfore my coolant would boil and therfore be spewing from my reservoir. And the funny thing is that the thermostat would sometimes open (I'd touch the bottom hose upon arriving at destination) but despite this, I was still running a higher than normal temp.

I've noticed that when ever the temp is stable at 100c° or 101c°, it would drop all the way to 95 or 96 if I'd do down shifts of 2 gears (sequentially from 5th to 4th to 3rd). And after I've replaced the radiator (there's a hole on my radiator), the temp would suddenly and totally randomly starts dropping from high 90s all the way down to 80c°.
And it'll again climb back up to the high 90s (quite rapidly).

I hope somebody here can help give me some advice as I've got nowhere else to turn to (mechanics in malaysia doesn't like working on ford vehicles). My car doesn't have oil in coolant and vice versa, no smoke from engine bay, no rough idling, no lost of power (not sure about compression) and dipstick doesn't show any signs of coolant being present. No leakages anywhere visible, don't think I'm losing any coolant (bcos I've tried bleeding the bloody thing so many times I can't remember the level my coolant was at anymore!)

Thank you for reading my extremely long post, any help/advice would be greatly appreciated.
 

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I’m having a similar issue with my 1.6L engine and I’m worried it’s running to hot as well. When you replaced the reservoir did you use the old Cap? The reservoir cap holds the pressure in this cooling system. If the cap is bad, the system won’t hold pressure. This lowers the boiling point making the water in the coolant mix more susceptible to boiling, and turning into steam. Steam can’t cool the engine though, it will eventually get burped up in the reservoir and more liquid will come into system but again without pressure the water will boil and evaporate. Coolant on its own is not as effective at high temp control which is why we mix it with water 50/50. Have you noticed you’ve been losing coolant? The cap might not be completely bad but going bad and when you installed the new reservoir, you had to move the cap, if it’s going bad maybe it intermittently malfunctions and won’t hold pressure. This is just an idea. You can test the caps ability to hold pressure with many coolant pressure tester kits. These are just ideas, Hope this helps!
 
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