Overheating problem

[MattHopkins]

We have recently bought a Ford Freda, 1999, 2.5 litre petrol/LPG. Last week it overheated on the motorway. When we pulled over, the coolant was pouring out of the overflow. There is no leak from any hose and it doesn't overheat or lose coolant when we keep to speeds under 40 mph. The mechanic we use strongly thinks it's a problem with the thermostat. Does this seem the most likely diagnosis? He has asked me to get him some pictures from the internet of the water system but I'm not very technically minded and have not got very far. Is anybody able to help me out? Thanks in advance.
Matthew

[Bob]

Welcome aboard, Mathew.

Someone with more techy knowledge than me will be along soon.

[MattHopkins]

Thanks

[Simon Jones]

Sorry to hear your news. The V6 is not known for overheating problems but it must be bleed using same process as the diesel. The thermostat is a reasonable place to start, but in normal operation it does not open, so driving faster is unlikely to be thermostat related as the increased speed has a much greater cooling effect. I'd recommend checking the waterpump is working correctly.

The thermostat is in the alloy housing on the front of the engine if you do want to check it out.

[MattHopkins]

Thanks for that - much appreciated