W202 C180 1995 overheating

[bravedude]

Hi everybody.
I've got a boiling coolant issue with my C180. I changed my head gasket last year november. The car has been good till now. At the speeds of 110 - 150 km/h, my coolant boils over and spills away. I changed the viscous coupling almost a month ago. But I've realised that at high temperatures the viscous coupling doesn't kick in. I may be wrong though. Please I need some advise.

 

[Hals1985]

Possibly thermostat, if electrical fan check connections to fan. If mechanical check/change the coupling between water pump and fan. I had an overheating issue on a 300zx and it was the heater element leaking and letting air into system. Work through cooling system in steps and check it all

 

[bravedude]

Thanks for the advise. I'll double check on cooling system. Today, driving back home just a 3.1 km drive, I was reading high temps. Just above the 3/4 mark. I decided to take some shots of cooling holes. Just at the thermostat I noticed a the tube has swelled up. I immediate suspicion is the thermostat. I maybe wrong though. Mid last year, I fixed a new thermostat. On the old (original) was written 87 C but new one (analog) was specified 77 C. Could this also be the cause? Please, need some advise. Thanks.