4ag running cold

[bmak]

the motor in my hatch has been running too cold for ages now. Its fine around town & at idle it sits about half way but as soon as you hit open road (3k and over) the temp drops down to cold. Heater blows cold air etc. The radiator is cold to touch & so is bottom hose. The top hose is hot at all times.

As soon as you slow down temp comes back up, thermostat opens etc.

Thermostat was replaced & seems to work fine & i tried blocking part of the radiator & that helped keep temp up.

What else could it be? It like its getting too much flow at revs but everything is factory.

[spectral]

I presume you've actually sighted the thermostat and made sure its not stuck open? its probably the only thing that can give that type of behaviour.

[bmak]

No but the fact that its not very old & the bottom hose stays cold when the top is hot i assumed its working. I was going to buy another one anyway in case its doing funny things.

[c2888]

WARNING DO NOT OPEN A HOT RADIATOR!

now that is out of the way, you can quickly determine whether your thermostat is busted and not working. Pop the cap off the radiator, and kick it in the nuts (turn the key baz) From cold you shouldn't see any fast movement in the coolant. It will ebb and come up and down as it heats up, but it won't have any significant flow. If it is flowing as cold temperature, your thermostat is open and you should replace him.

From what you are describing, it seems you are describing the thermoswitch as the thermostat. The thermoswitch is the little screw in thingy in the thermostat housing, controls the fans, and the thermostat controls water flow from radiator into the head. Most thermostats have 82deg c stamped into them, so you should have heat ALL the time (after it's warmed up of course) if your thermostat is working.

Dan

[bmak]

No water flow when cold as Ive already checked that. It warms up heater, throttle body etc real quick when 1st started & idled that's why i assume thermostat is ok.

But as soon as i drive fast temp goes way down to cold again.

BTW a mates car that has my old RWD 4ag does the exact same thing. He has had it looked at by many people that have changed sensors, thermostats & other pointless stuff. his is so bad when he first comes back to idle it revs at 2k until the TB heats up again.