My car had a front under chassis damage which was caused by driven over a tree stub at around 40km/h. It was then towed to a workshop to get fixed.
After a HUGE bill, I collected my car. On the day, 20min after I just got it back, there was a lot of water leak appeared somewhere under the engine which I found out when I just parked my car. I called the workshop immediately and they told me it was because they put too much water and I should keep driving.
On the next day, I was driving cautiously at around 2000rpm 60kmh with my eyes staring at the temp gauge. After 15min suddenly there was a strong smell coming into the cabin, it was like some rubber or plastic melting. So I stopped and opened the bonnet. The top of radiator(plastic), where the hose is clamped, is cracked and smoking white smoke. The temperature of the smoke and the engine was high, but the temp gauge still stayed normal. I called the workshop, they told me to drive to their workshop to check.
A week later I was told the gasket was blown and the upper engine maybe broken which is best to just replace the engine, all at my cost. They said the gasket was blown due to high temperature and was caused by broken water pump which was not able to 'see' when they repaired the car. However, the driver is fully responsible due to the neglection on the temperature gauge that he(me) kept driving when the temp is so high.
My questions here:
Given that 1. The temperature gauge always stayed at normal when I drove it 2. The car had also been working very 'smoothly' at low rev(i did not rev high during that 2 days I had the car)
What could be the cause for the blown head gasket? And why did the temperature gauge always stayed normal all the time(i also noticed on the second day, the temp gauge took a relatively very short time to raise to its normal position when warming up)?