Is the coolant light tied to the gauge?

[Mike T]

How directly is the low coolant light tied to the temp gauge? After replacing the 1&2 head gasket, and bleeding the system this 1.9 fills the overflow tank, and after 15 minutes driving, the light blinks and the gauge skyrockets. Sometimes, after pulling over the coolant level is ok and engine feels normal temp. I've replaced the expansion tank and re-bled the system several times. Any ideas? Mike T

[weinerwagen]

The red light flashing should come in from the signal at the rear water bottle with the cap....

the temp guage is getting its signal off the thermostat housing...but if it gets too hot it will override the coolant level sensor and start flashing at you, but if you have air in the system it should come back down quickly...the air pockets are causing the skyrocketing and up and down coolant temp...UNLESS you have a bad thermostat. Is it opening up? I know its hard to tell if they are working, but maybe its defective and not opening up right...new ones will be defective but it is rare.

the skyrocketing is an air pocket...lift the engine up over night, try and get the air to bleed out the back. Its a common issue with the 1.9s. I've had mine gurgling inside the motor from borderline overheat yet the radiator is cold. AIr pockets. Keep trying to force the air to the top either at the front of the radiator or the rear...Air should bleed off after a couple of hours of running...

You open up the heaters too?

[Mike T]

I understand where each gets their signal from, but wondered if the relay tied the two together, making the gauge rise simultaneously.

[weinerwagen]

Check the next time it goes wayyyyyy up, stop and check that motor. Turn it off, do you hear gurgling inside the engine, (its boiling)...if not, or the motor is not hot, then you have an electrical issue. But if it is using fluids then there is a good chance the thermostat is stuck or air pockets.

Then check the connection at the thermostat housing, its the small one. Make sure its not frayed or loose. Does it do it again....? Check to make sure the thermostat is opening. It could be that the thermostat is staying closed cauing the engine to overheat. You should be able to tell if it is getting hot...It might blow fluid out the cap. With the engine idling and with the lite flashing, can you fiddle with the connection in the back to see if the guage reacts? Dont get your fingers in the water pump pully, but you might check the contacts to see if the guage is reacting to you playing with the connection...

If the connection is good, and the sensor is not acting up, then its air in the system. Or thermostat stuck closed.

In my experience, the temp climbs steadlily...not instantly or within a 2 second time period...more in the minutes... when the engine is overheating with a stuck thermostat or air pockets.

I had an 1.9 boil on me several times, but the temp guage took several minutes of steady climbing before the red light started flashing. I walked to the front, turned the engine off, went back and could hear the engine boiling inside the case.

I let it cool, it needed another gallon of anti freesze and off it went, several trips to Phx from Central Cal...

[Mike T]

The thermostat seems to open normally, send hot coolant north to the radiator. What puzzles me is the gauge climbs normally, to about a third up and stays there, behaving itself until suddenly the light starts flashing and the gauge simultaneously zooms to the top. The engine and radiator feel normally warm and the coolant fan cycles on and off normally. Stumps me...[/list]

[walrus]

Maybe bad sensor or connection which breaks down after getting hot.