Golf Mk3 1.8 running hot

[GazBrad]

Hi all
I've got a Golf Mk3 1.8 1994 that's done about 145,000 miles. The engine's pretty sweet still but recently I had to have the head gasket replaced and ever since it's been running very hot with the gauge going well to the right.

The coolant level's fine as is the the radiator and the hoses and I can't figure out what's going on. After a motorway blast at about 80ish it flashes up the oil light for a few seconds after returning to normal speeds indicating high operating temperatures. The oil level's fine by the way it's just the coolant temperature that sets this off. Additionally from cold the engine's very hesitant and rough until it warms, are these connected?

Bearing in mind most things might be wearing out now around the engine bay, what does anyone think is going on here?
Any help appreciated.

[jp_paul]

It might be worth your while to remove your thermostat and check its fully operation in some boiling water. Also flush your coolant system out. Are you running on 100% water? as this will cause a higher operating temp than a water/antifreeze mix (antifreeze has superior heat displacement capacity). Failing all of those, try checking the resistance of your temp sender in the thermostat housing at cold and hot. A Haynes manual may tell you the correct resistance you should find.
Hope that helps

[GazBrad]

Thanks for the feedback. The thermostat was changed at the same time as I had the head gasket done, it could be faulty though. I had the winter antifreeze put in at this service as well so that's covered. I'll have a look at that temp sender like you said, it's those things that make you think it's something bigger sometimes, thanks again.