can I kindly ask your opinion on my car issue? I'm not deep in field of engines and this problem is causing my serious headache and a total waste of cash without any results.
I've a 2015 VW Polo TDI. All began with cars signaling a low cooler levels, but I was in a hurry and 60 miles away from home so I decided to came back monitoring engine temps on the car's computer anyway. During the way back the engine never had gone back over 90° Celsius. When at home I refilled the expansion tank (was empty) and immediately leaked. So I took it to mechanic, which diagnosed radiator failing because damaged by metal debris on the street floor (what a luck). I saw the broken part. So we proceeded with new one.
When I got back the car I immediately noticed that levels of cooler was 2 inch above the maximum in the tank: he said isn't a problem. While casual city driving in the next days I immediately got a new problem: randomly after a while, during driving (maybe 5 - 15 miles) engine temps ramped to over 100° Celsius and air cooling fan was activated at maximum speed.
I took the car back in store, and mechanic said that was a problem of termostatic valve of cooler system and changed it with a new. Problem again, exactly the same (I monitored that he made quite a lot of miles, so I assume he was testing it).
Took back in, it changed termostatic sensor. Again tests done, again problem.
Took back in and he dropped a car to VW colleagues for a new plunging in the cooler system (everytime this was done) and he said that the replacement sensor was fault and changed it again. Problem after 2 days of normal use was back. More interstingly when I took the car yesterday with the issue "live" (engine over 100°C) coolant wasn't boiling and when we made some engine speed test temp was rising, but after just some seconds, turn off and turn on again temp was 90°C.
Now he is saying that it's surely a problem of blown head gasket, probably caused by my initial trip back home.
I'm a medic and I recently moved so I do not have any mechanic of trust nearby. What it leaves me really bothered is that he seems to proceed by trial and error and from what I googled blown head gasket is a serious problem with really evident symptoms, which are totally absent. I'm really afraid to leave the car stopped for maintenace another month (2 months now) and spend again $2000 more ($1000 spent already) on a car that is $9000 worth now.
What you would do? May the overfilled cooler tank be the cause?
update 1! Done what Steve Matthews suggested and the solution seems to be near. With cold engine I've turned on the car, heater at maximum temperature maximum vent, removed 0,5L of coolant exceeding the maximum line in the ball tank. With cap open, squeezed the bottom hose and 2 bubbles burped out. Test drive#1: 5 miles all ok. Test drive#2: 10 miles all ok. Test drive#3: 10 miles and suddendly again the temp ramped with obvious turning on of the fan. With issue present opened car hood: ball tank of coolant not boiling (neither very hot), level above 1/2 inch above the max and when I turn on at maximum the heaters problem disappears (temp returning suddendly to 90°C).
Final update A late update, just to share the solution with everyone. I brought the car to my old mechanic and he said that was the previous bad work that caused water pump fail that he fixed. He also unmounted the head gasket to make sure that all was right. Shed another 1200$ but problem was gone then. I can't totally trust what he said, but that's all.