So here is a cooling system and engine temperature issue thread. Read this before posting on your over heating car and such. I will also outline the commonly failing thermostat. So here's the issues:
-Check that your fans are cycling (If not check your fuse in position 19 for your radiator fans, check your thermoswitch is functioning on lower radiator, or check the fan motor itself)
-Check that you're not low on coolant and that the concentration is 50/50.
-Clogged coolant hoses or plugged radiator. If it only over heats at highway speeds sometimes the lower radiator hose collapses at highway speeds.
-Worst case scenario your head gasket could be blown.
-Thermostat is stuck closed
-Radiator fins could be full of bugs/ dirt etc; clean it out.
-Worn out water pump thus not being able to circulate coolant correctly.
-The only thing that will cause this is a thermostat stuck open, which i will go over right after this.
Thermostat symptoms and replacing (ABA Engine)
The thermostat tends to get stuck open on these 2L engines frequently and will cause the below symptoms. It will cause poor gas mileage and cause your engine oil to start sludging as well as lower than normal heater output. Mine was stuck open so i decided to change it. Its a tedious and dirty job if you're doing it by yourself with a jack on the garage floor. It took me 2 hours on my first time, with no breaks. So here's how it boils down:
Thermostat stuck open
-Will drop in temperature while driving at highway speeds and temperature will fluctuate.
-Will warm up SLOW, if it takes 10 minutes for your car to warm up on a hot day then its stuck open.
-Its simple your car will overheat since your thermostat is stuck closed and won't circulate coolant when it starts to over heat.
First of all you will need the following for the job, i am not going into detail about belt removal. If you have only basic knowledge of working on cars, leave this job to the pros!(I am using tools in metric not imperial.):
-3L of coolant (VW pink G12 coolant) and 3L of water (Cooling system has a 5.8L capacity)
-Thermostat and O-ring
-Thermostat housing (Cheap part, tends to break and warp during removal)
-13mm wrench (For alternator tensioner)
-10mm socket (Thermostat housing), 13mm socket (All power steering bolts except 1), 16mm socket (Bolt that holds power steering pump to main bracket)
-22 mm socket for power steering pump tensioner cog.
1. Use your 13mm wrench to move tensioner away from you and let the serpentine belt hang.
2.Loosen all bolts holding power steering pump to the pivot bracket and use the cog to remove tension on the power steering belt. Don't try and turn the cog if all the bolts aren't loose or removed, you will strip the cog, it's soft metal. Then remove belt off the car, i left the serpentine belt just hanging on pulleys.
3. Now that belt is off, remove the 3 bolts that hold the power steering pump and bracket to the block. Once this is done the pump will drop and you can just let it hang, NO NEED TO DISCONNECT ANY POWER STEERING HOSES.
4. Open the expansion tank for coolant and get ready to drain it. Now that P/S pump is hanging, you will see the thermostat housing right about where P/S pump was. Now disconnect the coolant hose that is connected to thermostat housing and coolant will drain out of the system.
5. Use your 10mm socket to remove two bolts on thermostat housing (I used penetrating fluid to loosen these up, just in case). Pull the housing off and VOILA there is the thermostat, simply pull the thermostat right out. Might give you some trouble so use pliers if needed.
5. Put the new thermostat in, and O-ring on after the thermostat is in place (NOTE: The thermostat will not stay in place until you put thermostat housing back on. The O-ring is tough to keep in place with out it dropping out(Very frustrating), but keep trying it will happen.)
6. Now everything is the reverse of removal, good luck!
You will notice the difference in warming up time right away, its crazy
Power steering pump bolt info: