HI there I am new to the group and have a problem with my wifes 94 Honda civic...The coolant reservoir over flows after a 50 mile trip..The thermostat has been changed and the cooling fan comes on for about 3 minutes after it reaches about half way hot on the gauge.. My question is can the thermostat sender unit be bad , causing the vehicle to run hotter then it should not allowing the cooling fan to stay on long enough? I would like to know how long that cooling fan should run for ..? Or can there be a clog somewhere not allowing the system to function properly ? The radiator was also changed a few months back....Thank you so much for any response... ,,bill gray..

 

welcome to the forum. when your coolant reservoir overflows, does it also blow a lot of bubbles? The cooling fan goes on when the temp gets to a certain temp, and stays on until the water temp goes back down. 3 min seems a bit short. How many miles does the engine have, and check to see if the radiator produces a lot of air.

 

Thank you Acmech for your response... It was a bit bubbly when it was overflowing out of the reservoir. How can i stop the radiator from producing air? Is there a way to bleed it? Thank you again for your response..,bill

 

the bubbling is caused by the compression stroke of the piston pushing compressed air past the head gasket into the water system.. with a high milage car, this cannot be helped other than replacing the head gasket. I'll do some research to see if there might be anything else that can be done.

 

Thanking you again Acmech for your response.... The vehicle has just over 100,000 miles on it.... It seems to lose about 1 cup of coolant per trip ... I also wonder about the sensor that tells the cooling fans to come on.. Could that be faulty and not allowing the fan to come on long enough for the system to cool? Is there a way to check the run time for that sensor? If i do a compression test on the cylinders , will that show if the head gasket is bad? Thank you so much for your kind help ,Bill

 

The fan goes on at a temp the sensor is set for and turns off when the low end of the temp is reached. A cooler thermostate will keep the coolant cooler, but during winter sometimes it is not warm enough ( eastern states ) If you do a compression check and view the rad, you may see where the bubbles are coming from. Normally the sensor goes bad, the fan does not come on at all. My neighbor put in stop leak and stopped his headgasket from leaking, but this also may cause the rad to stop up.

 

Barsleak makes a great product for head gasket problems.. i put some in my dad's 1998 F-150 Tritan V8 when the head gasket started to leak and its been running strong now for almost 18k miles.

 

thank you very much acmech and hayden...I have been off the internet for a bit ,with the flu....I sure appreciate your kind help and will try both ..... Bye for now and I will get back to work on that vehicle after i shake this cold... Thanking you Both ..., bill