UPDATE: This problem has been resolved, needed to bleed the system.

Background:
My water temp was running high last week after a drive and I got that soul crushing wisp of steam from under the hood. Turns out that the hose that runs from the expansion tank to the thermostat housing had a breach and and had sprayed that area of the engine compartment with anti-freeze. No problem – replaced the hose, topped up the system.

Today:
During a very short drive, the water temp needle quite quickly went up and the warning light came on and I pulled over. This was odd. On inspection, the expansion tank didn't seem particularly hot and the fan didn't come on. I don't have one of those fancy infrared thermometers so couldn't get a measure on the actual temp. But could it be that the temp sensor is bad?

Anything I should be checking? Any help very much appreciated, thanks.

 

Are you sure it's circulating?

 

Thanks for your reply Kiln_Red. It turns out that I was low on fluid. I guess I lost more anti-freeze than I thought. Took it for a drive and all seems well now. I guess it takes a while for the fluid to get around the system .

 

Just needed to bleed coolant system.

 

HF has them for about $20, discounted to maybe $12 or so on sale.

Super duper handy thing to have for lots of reasons. not just radiator/cooling system. Not even just 'car stuff'.

 

First thing before anything: New radiator cap. They can cause exactly the symptoms you are having.

 

did i miss something? it sounds to me like your thermostat is bad. if it isn't opening, heat/pressure build up and it will find a way out, through the cap and possibly through leaks it will create

 

Even though you issue has been solved, for future reference for anyone replacing a thermostat make sure it is installed with the little hole on top.

Otherwise it wont bleed and will cause it to overheat.