My car started overheating. I checked the top radiator hose and it was hot, the bottom radiator hose was closed. I assumed that the thermostat was stuck so I changed it. After changing it I took it for a test drive, it started over heating again, when I pulled in my driveway, the radiator blew coolant out from the middle.I checked both the hoses and they were both hot. I just changed my water pump 6 months ago. what is the problem/
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It may also be the temperature sensor.
Not knowing your model, if it uses both a belt driven and electric fan, the electric fan (or its sensor) may have failed.
Turn on the AC to see if the electric fan will cycle as it should since this is used (in most vehicles) for engine cooling if the main fan isn't adequate whether AC is in use or not.
On high mileage engines if distilled water was not used instead of tap water (along with coolant), the radiator core can eventually become clogged with calcium deposits. .
CAR OVERHEATING FIRST CHECK FOR LOW COOLANT IN THE RADIATOR COOLANT OVERFLOW JUG.IF COOLANT LEVEL IN OVERFLOW JUG LOW REFILL ADD COOLANT BACK TO THE FULL COLD MARK.PUT RADAITOR CAP ON COOLANT OVERFLOW JUG START ENGINE LET IT IDLE UNTIL IT OPERATING TEMPERATURE.MAKE SURE TOP RADIATOR HOSE GETTING HOT WHILE ENGINE WARM UP.IF TOP RADIATOR HOSE DONT GET HOT WHILE ENGINE IDLING YOUR THERMOSTAT COULD BE STUCK CLOSE CAUSING CAR TO OVERHEAT.IF TOP HOSE IS GETTING HOT.CHECK FOR COOLANT LEAKS CHECK TOP RADIATOR HOSE AND BOTTOM RADIATOR HOSE FOR LEAKS.CHECK FOR LEAKS AT THE RADIATOR CORES AND PLASTIC SIDE CONTAINERS.IF ALL IS GOOD ENGINE OVERHEATING WHILE IN A LONG TRAFFIC LINE, COOLANT FANS NOT COMING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR BLOWN COOLING FAN FUSE OR RELAY.COULD HAVE PCM FAULT.MAKE COOLING FAN ELECTRICAL CONNECTORS AND WIRING NOT DAMAGE OR BROKEN.
YOU NEED BLEED COOLANT SYSTEM.CHECK COOLANT LEVEL IN RADIATOR.ADD MORE DEXCOOL UNTIL COOLANT LEVEL IS CLOSE TO RADIATOR SPOUT.CRANK ENGINE LET IDLE UNTIL TOP RADIATOR HOSE GET HOT.WATCH TEMPERATURE GAUGE.IF TEMPERATURE GAUGE START RISING TO HOT ZONE.TURN OFF ENGINE.LET COOL DOWN.USE LARGE RAG SLOWLY OPEN RADIATOR CAP A LITTLE AT A TIME UNTIL ALL PRESSURE RELIEVED.REMOVE RADIATOR CAP.ADD MORE COOLANT.CRANK CAR AGAIN LET IDLE UNTIL TOP RADIATOR GET HOT.KEEP EYE ON TEMP.GAUGE ALSO.WHEN TEMP.GAUGE STOP CLIMBING.YOUR COOLANT SYSTEM BLED.WHEN DONE LET CAR SET A WHILE CHECK COOLANT LEVEL.ALSO FIRST THING IN THE MORNING CHECK COOLANT LEVEL AGAIN.AND BESURE ADD COOLANT IN THE OVERFLOW JUG TO THE COLD MARK.DONT OVER FILL THE COOLANT RESERVOIR JUG.WORK SAFELY DONT GET SCALDED.
Run the engine and look at the header tank , is there lots of air bubbles coming back out of the water if is then the head gasket may have split and that is down to either a can of Radweld or a strip down repair
If the radiator is not uniformly hot them I would go for that as your problem
Normal operation is that the engine starts the thermostat is closed , engine block heats up and opens water starts to circulate around the block
So to check that you need to fill the radiator with cold water run it for a few minutes check the bottom hose it should be cold
The stat opens and the bottom hose should get hot as the water from the block is pumped into the radiator for cooling.
The radiator should get hot all over and the cooling fan should kick in when the sensor hits the over limit stop.
If that does not happen then get someone to remove the stat altogether (It is only there to get the engine block warm quickly in cold regions )
In which case the bottom hose should go from cold to warm to hot
The thermostat is bolted into the bottom of the water pump, the lower radiator hose connects to a cover that holds the thermostat to the water pump.
the thermostat can be difficult to get at because the AC and power steering pump are all bolted on top of the water pump,
Your problem may not be a bad thermostat. I would also check:
1) water pump, some of the vw pumps are poorly made & tend to go bad.
2) fans belts, it can be tricky to get the right tension on these belts due to a badly designed tensioner system on the power steering & water pump belt.
3) hoses, radiator, coolant tank,. the radiators and coolant tank tend to leak when they get old, the plastic cracks or the rubber seals go bad. Also check the electrical system controlling the engine cooling fans. there are sensors and relays that can go bad. I have owned 8 vw's most of the major problems with these cars was due to electical problems.
4) Engine problems such as a blown head gaskets, or ignition timing problems can cause overheating. luckily VW engines usually don't have these problems, unlike other companies 4 cylinder engines (the Dodge Neons for example)
You'll have to remove the radiator (it isn't that hard) and take it to a Yellow Page listed radiator repair shop...Be prepared to spend $200, less if you're lucky...Don't forget to put water pump lube (NAPA #13 - looks like milk) in the radiator after replacing the fluid 50/50 mix