Avensis engine running cold

[Londonavensis]

Hello all, just joined the forum today!

Bit of a weird one this, involving a cold engine and air conditioning: My 2.0 petrol Tspirit 2003 runs very cold (according to the temperature gauge which hardly moves from the cold position) The heating is also very ineffective, hardly ever warms up.

I mostly have the air conditioning turned ON to stop the windscreen from steaming up and noticed today that if I turn the air con OFF within a few minutes the temp gauge moves towards the middle of the gauge (where it should be) and the heating becomes nice and warm. But when I turn the air con back ON again, within a couple of minutes the temperature gauge goes right back down and the heating gets cold again! 

I'm thinking a change of engine thermostat might help but any advice or thoughts would be welcome!

[fastbob72]

Hi there,if you find the temperature is barely rising above cold,on the gauge aswell as your heater blowing cool air despite being set to the hot position then 99 times out of 100 it's a blown thermostat. 

 

They have been designed to fail open (safe) for a long time now meaning your coolant will be flowing through to the radiator all the time

Normally it is closed when the engine is cold so the coolant is pumped around the engine internals and possibly the heater matrix allowing it to heat up more quickly. 

The thermostat platebis held shut by basically a metal spring that expands as the hot coolant heats it up,the hotter the more it expands until at the required water temp it opens up fully to allow the hot coolant to flow to the radiator as so ot doesn't overhead. 

When they fail they fail open as it's far better the coolant is cool rather than unable to cool down when it's boiling.

It's a very simple but ultimately very effective system much like the bi-metallic spring used to operate the automatic choke on the the Weber twin choke carbs...... maybe that kind of tech is too old for most folks to remember these days lol. 

Anyway, I'd check your thermostat first. You can drop it, once removed, into a glass of boiling water and see if it closes or just fit a new one and see if that sorts the problem. From your description I'd fit a new one expecting that to sort it because it sounds like a classic blown thermostat...... it's probably arounf £15-25, last time I bought one anyway :)