Thermostat Trouble

[sadako]

Right, Last night on the way home from work I noticed that my temp was down a little. The engine normally runs the temp half way up, it was just over a third. I put this down to it being a cold night.

This morning on the way to work, I get thge car up to temperature, Got on the motorway and wondered why my heater was getting cold. Looked at the temp and it was less than one quarter. Stopped to check for leaks and it crept back up.

My hypothesis is my thermostat has jammed open and water is running always through the radiator, even if it is too cold. When I stop, no air is flowing through the radiator and it heats up.

Apart from the choke coming on and messing up my fuel economy will this damage my engine? I went in today at 60mph with the heater turned off to try and keep the temp up enough, I am also considering slipping some cardboard over the rad to restrict airflow a little. Could anyone please advise if my hypothesis is correct and roughly how easy it would be to fix.

[DeltaFox]

Could be the thermostat. Could also be a sludged up heater matrix or a big air lock in the system.

Thermostat alone wont damage the engine, at least not if its jammed open (overcooling) but an airlock certainly may cause some if not attended to.
HTH

[GreenV8S]

sadako said:

My hypothesis is my thermostat has jammed open and water is running always through the radiator, even if it is too cold. When I stop, no air is flowing through the radiator and it heats up.

That sounds quite likely. But any time the heater runs cold, consider the possibility that it is because you don't have any water circulation. If this happens the engine will overheat quite rapidly. If the heater warms up again as soon as you slow down, that would tend to confirm your theory.

[sadako]

I believe the heater gets warmer, Since I currently have access to lab equipment I will see if I can borrow a thermometer for a day. The temperature gague definatly is speed dependant right now. When I stop it warms up. I also think it takes its reading right near the engine. I will not rule out the possibility of air in the system although I havnt been able to hear any since my coolant leak was fixed last month - I hink the mechanic bled the last of it out then. However whilst getting some air out when the coolant leak occured I may have dislodged some scale which could have jammed it.

Should I consider a defective water pump?

Is there anything i can do to descale/clean the system without naffing up the gaskets?

A flush is definatly going to happen. The coolant is looking pretty grim in the system and its only been in there a few months

[sadako]

Update: The heater is definatly getting hotter as the gauge goes up. I dont think we are looking at an airlock here. If I were to open the engine bay bleed valve to check should I do that with the engine running or not? I would imagine pressure would be needed but there should be enough if the engine is hot but turned off, However all I have is theory on how things work and no practice. I will contact my mechanic ASAP to see if he can book me in.