Cooling system temp light comes on and car overheats. the bottom hose is cold and top is hot. the fan runs when I shut the car off, but i don't think it runs while the car is running. I let it idle and it overheated whithout the fan ever turning on any ideas PLEASE HELP!

First thing to check when the engine is cold is that if there is enough antifreeze in the radiator and after you run the engine for about 5/10 minuter check both the rad hoses to see if they are both at the same temperature, if the return hose which is the bottom one is cold then replace the thermostat. If both hoses are hot or same temp then make sure the radiator fan comes on?

What are you going by to say it's overheating , temp gauge ? Have you test to see what the actual temp. is > Hook - up a scan tool ,what's the PCM - engine computer seeing for engine temp. ? 223 degress the PCM should turn on the cooling fan . You could buy a Non-Contact Infrared Thermometer With Laser Targeting at harbor freight ! Radiator very hot ????? What is the right temp .
Non Contact Infrared Thermometer With Laser Targeting

Could be a bad temp gauge . Is the coolant surging inside the cooling system ? Does it have a radiator cap ? Have you replaced it ?

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

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Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

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MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

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A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

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sounds like a clogged radiator if there's no water to the top hose, also I would replace your thermostat just in case. What you can do is run your car till it get warm , shut it off, and feel all of your radiator with your hand to see if some parts are cold, then it's a clogged radiator. but it should overheat also check your coolant temp sensor to make sure it's correct. Also just look at the motor and feel it, if it's extremely hot and cannot touch it, then it's overheating.

only the top hose gets hot m8 means the therm is opening up like its needs to do. i think your temp sensor/ sending unit is on the fritz

is the rad fan working??

When you mention the radiator having a hot upper in pipe and a cool bottom out pipe tells me that the coolant is not moving around the engine. This could be down to a water pump not working, blocked radiator, thermostat not opening. The bottom hose should be cooler than the top hose but once the engine is up to working temp which is around 85/90 degrees c for an audi the bottom still should be farly hot to touch. Hope this helps

You say it gets hot and overheats, are you losing coolant when it overheats? If it isn't boiling over, you seemed to cover everything that could be wrong, the fan is working, if it is not boiling over, just registering hot on the gauge, I wonder if it's just a temp. sending unit that's bad, indicating a overheating problem when there really isn't one. The water pump is bad when the shaft bearings go bad, and it will leak at that point. So, let me know if the car is actually boiling over (steam visible, exiting the cooling system)

um...strange ...engine temp reaches 210 before thermostat opens and lets water circulate ..fans go on before that normally..180 or so..hot air from heater going to cold air? strange...could you elaborate for me /us?

turn your heater on to max heat and high fan. then see if you can feel the hoses on the firewall for heat they should be hot. make sure that the fan unit on the radiatoris working if the upper radiator hose is hot the fans should be running if they are not that means that either the relay is bad the thermo sensor is bad or the fan unit is shot... please rate the solution..........thanks

Hi, I think you have an airlock in the pump,You need to drain the water totaly when stone cold.Drain radiator and disconect hoses from waterpump and top hose from themostat. Reconect pump hose and add water slowly into radiator through top hose untill rad is full then squeeze bottom hose vigourously,You ll feel the water tension in the hose, Connect all hoses and top up water level. This must be done cold as hot and cold water will cause an airlock. Hope this helps you out.All the best.Phil