Temp Gauge Reads Cold Unless Idling

[cp[mike]]

This doesn't make a whole lot of sense. If the thermostat is stuck open, and your engine has warmed up completely, you should have not fluctuation you speak of.

The theory only makes sense if your engine hasn't had time to warm up. And with the thermostat stuck open, it should take a long time to warm up.

Actually, it makes no sense either way.

if you leave the thermostat open so coolant is always circulating through the radiator, if you are driving down the road, it will cool it down enough to make it so the engine runs colder than normal and the gauge will point to C.

the thermostat closes and lets the motor run without circulating coolant, so it heats itself up with no cooling ability, and it only opens and lets the motor cool down if its getting TOO hot. thats how it regulates engine operating temp.

if hes sitting still, the radiator is getting no air and isnt cooling down the coolant, so its basically as if the motor is running with the thermostat closed, and the needle will rise and itll run warm. once it gets too warm, the fans kick on, creating air movement across the radiator to cool things down.

the fact that his heat blows cold and his idle never drops shows that the coolant is staying too cold... a sign that its passing through the radiator even when it isnt supposed to...

[MRX]

hopefully this is my problem, but mines a bit different...

Motor warms up within 4-5 minutes
Drives fine, temp gauge stays normal UNTIL i either give it heavy throttle or go into boost. As soon as i let off the gas and drive normally again the temp gauge goes back to normal. Fans come on when they're supposed to and all. I've also got a Jackson Racing thermostat in there so i'll put a stock thermo in it and see how it does. I think i'll re-bleed it first tho.

[F22-GURU]

if you leave the thermostat open so coolant is always circulating through the radiator, if you are driving down the road, it will cool it down enough to make it so the engine runs colder than normal and the gauge will point to C.

the thermostat closes and lets the motor run without circulating coolant, so it heats itself up with no cooling ability, and it only opens and lets the motor cool down if its getting TOO hot. thats how it regulates engine operating temp.

if hes sitting still, the radiator is getting no air and isnt cooling down the coolant, so its basically as if the motor is running with the thermostat closed, and the needle will rise and itll run warm. once it gets too warm, the fans kick on, creating air movement across the radiator to cool things down.

the fact that his heat blows cold and his idle never drops shows that the coolant is staying too cold... a sign that its passing through the radiator even when it isnt supposed to...

Excellent Answer!! Couldn't have explained it better myself!!
All comes down to proper circulation.

[4CYLPOWER92]

if you leave the thermostat open so coolant is always circulating through the radiator, if you are driving down the road, it will cool it down enough to make it so the engine runs colder than normal and the gauge will point to C.

the thermostat closes and lets the motor run without circulating coolant, so it heats itself up with no cooling ability, and it only opens and lets the motor cool down if its getting TOO hot. thats how it regulates engine operating temp.

if hes sitting still, the radiator is getting no air and isnt cooling down the coolant, so its basically as if the motor is running with the thermostat closed, and the needle will rise and itll run warm. once it gets too warm, the fans kick on, creating air movement across the radiator to cool things down.

the fact that his heat blows cold and his idle never drops shows that the coolant is staying too cold... a sign that its passing through the radiator even when it isnt supposed to...

I was under the impression that the thermostat is only closed when the engine is cold, such as when the car is first started in the morning. Then when the engine reaches normal operating temperature the thermostat opens.

Is it true that all thermostats close while we are driving, and only open when we are stopped? Even though the engine it still at normal operating temperature while driving on the freeway?

[cp[mike]]

Is it true that all thermostats close while we are driving, and only open when we are stopped? Even though the engine it still at normal operating temperature while driving on the freeway?

if it needs to close, it will. if the thermostat was open on the freeway, i can tell you that the engine wont be at normal operating temperature, the needle will be down at C (ive driven a car for a couple weeks with no thermostat at all)... so if the engine is getting too hot, the thermostat opens hoping there is air flowing across the radiator. if not and the engine is still too hot, the fans will kick on. if the engine is too cold, the tstat closes and lets it warm up.

its a constant cycle, depends on the temperature outside, how long you sit at a red light, etc.

[ray ray]

I forgot Accordinate. Don't forget to turn the heater knob all the way to hot, so that you don't trap any air in the heater core.

4CYLPOWER92 - A thermostat isn't an off and on switch, it varies the amount it opens with coolant temp. If the coolant gets to hot, the metal expands and allows more coolant to flow through the system cooling the engine and causing the thermostat to contract restricting the flow, allowing the temp to rise or stay the same.

As speed and airflow increase, the thermostat will contract, restricting flow and resulting in the engine temp remaining constant.by the way this owequitit im on rayray's computer.

[F22-GURU]

4CYLPOWER92 - A thermostat isn't an off and on switch, it varies the amount it opens with coolant temp. If the coolant gets to hot, the metal expands and allows more coolant to flow through the system cooling the engine and causing the thermostat to contract restricting the flow, allowing the temp to rise or stay the same.

Or you could call it a "Coolant Temperature & Flow Regulator".
'4CYLPOWER92', I hope this has cleared it all up for you.

[4CYLPOWER92]

Okay, learned something new. I knew the thermostat is not an on/off switch, I just thought that the engine at normal operating temp was hot enough for the thermostat to stay open, regardless of other conditions.