This thread is a classic example of
- "fix it before you even know what is wrong"
or
- "repair comes before diagnosis"
Although I have lots of sympathy with the OP, we can all learn from this experience.
Don't start fixing before you are 100% sure of the problem.
Workshops are way to willing to try all options of replacement at the owner's cost.
For this reason, I always advise to be specific when giving a workshop instructions.
In this case the owner (incorrectly) diagnosed his vehicle as suffering from some or other "overheating" problem.
I'm still not sure whether it did overheat or not, or whether the gauge is/was broken.
The correct diagnosis would have been: "The gauge fluctuates".
If it was due to overheating, fair enough.
The moment the owner does the diagnosis, he exonerates the workshop of finding the cause of the problem, and is liable for all costs.
On the other hand (Dêrren), if the workshop makes an incorrect diagnosis, the owner could and should refuse to pay the cost.