citroen c3 overheating Help!!!!

first of all let me say Hi as i am new to the forum

well, where do i start
I purchased a used car from a trader in September 2016 Citroen c3 1.1 desire when I bought it it had only done 36000 mile on a 06 plate 10 year old
just before Christmas it started overheating coolant went brown so i got the cylinder head done new water pump and timing belt cost me £540
still was overheating the garage expected it was the temp sensor
so he replaced that, that cost me £50
and still it it says it over heating
when it does it i have been driving on the motorway
i have took it to the garage were the work as been done and they cant place where the fault is does anyone have any other ideas

Welcome to the forum!

I have absolutely no experience with Citroens, but the cooling system is probably rather typical. As new as yours is, I'm expecting that it uses an electric cooling fan. When the engine is high on temperature, is the electric cooling fan running and moving air? Since the shop suspected the temp sensor, I'm wondering if they identified that the fan is not running. The temp sensor would have nothing to do with the engine actually overheating, unless it is preventing the fan from running.

Also, you mention that it overheats after you've been driving on the motorway. That makes me wonder if either the flow of coolant is insufficient (maybe due to a stuck or backward thermostat) or if the radiator is plugged or blocked or a hose is kinked somewhere. I'd be looking in to these types of issues, but these really are the basics. If your shop has not checked these already, you really should consider finding a different shop.

-Rod

The garage I took my car hooked it up to a diagnostics computer and drove it around the fan kicks in at the right time and does cool the engine but it still persists to come up on the dash board that it's overheating and you can hear the fan run when that happens thank you for your help

With that information, it sounds to me like the shop needs to focus on an obstruction of the radiator or an issue with the flow. They may have had the thermostat out when they changed out the head gasket.

-Rod