Need to change coolant or add antifreeze is only 20% -9 degrees in Audi 80 1.9TDI

it does not use antifreeze. you will need to buy Dexccol premixed 50/50 coolant. There is no universal coolant, use Dexcool only, it is red. you should never ever add water, only premixed coolant.
the premixed is good to -40 degrees F.

The drain plug on this radiator is plastic, nearly impossible to reach, and highly likely to leak if you do get it loose. I try to never loosen them up because of this. I would first test to see what the freeze point of the coolant is and then if you need to add some 100% antifreeze to lower the freeze point remove some coolant from the reserve tank and add the correct type of antifreeze back into it there. Use some sort of sucker to remove the coolant, DO NOT use your mouth on a hose to do so. Antifreeze is highly toxic. Coolant will circulate through the reserve [or degas tank as Ford calls it] and will eventually mix thoroughly with the rest of the coolant. -24F to -30F degrees is what the factory mix is usually good for. DO NOT add too much antifreeze as the correct blend is needed for the system to cool properly.

car over heating because thermostat faulty its stuck closed not opening allowing coolant flow from engine to radiator.hot climate need 50/50 antifreeze and water.straight water will boil away at 212 degrees. engine can get hot as 225 degrees you need add coolant to raise engine coolant boiling point temperature.

As long as the strength of the antifreeze is still at least -20 degrees, I wouldn't change it.The problem with flushing a coolant system and putting in new coolant is has a strong acid base and will start to eat at old freeze plugs in the engine,starting them to rust faster and then leaking your new coolant. You will be using Green antifreeze, not orange or yellow.

SOUND LIKE HEAD GASKET LEAK.CHECK ENGINE OIL FOR SIGNS ANTIFREEZE CONTAMINATION..OIL WILL LOOK LIKE MILK SHAKE.IF USING WATER IT EVAPORATES AT 212 DEGREES. ENGINE COOLANT TEMPERATURE CAN CLIMB UP TO 220 DEGREES.IF OIL IN CRANK CASE LOOKS GOOD.ADD 50/50 WATER AND ANTIFREEZE. ANTIFREEZE WILL RAISE BOILING POINT TO KEEP COOLANT FROM EVAPORATING.SEE IF YOU LOSING WATER ITS BOILING AWAY LIKE WATER IN A TEA KETTLE.

The GM recomend using GM Dex-Cool Red Coolant.
The matter of fact is that many consumers has filed out complaints againts GM Dex-Coll Reed Coolant.
http://www.consumeraffairs.com/news04/2006/08/gm_dexcool.html
http://www.consumeraffairs.com/news04/2008/09/dexcool_settle02.html
http://www.consumeraffairs.com/automotive/gm_dexcool.html
We replace it with:
ANY COLOR ANTIFREEZE
ALL MAKES ALL MODELS
of cars and light trucks
add to ANY color antifreeze
PRESTONE.

It's up to you. Ask before, but if you decide to change the type of coolant then:
If your intention is to add coolant only, then you need:
PRESTONE 50/50
PREDILUTED ANTIFREEZE/COOLANT

If your intention is to flush the RADIATOR (Cooling System), then you need:
Mix with
ANY COLOR ANTIFREEZE
ALL MAKES ALL MODELS
of cars and light trucks
add to ANY color antifrezze
PRESTONE
EXTENDED LIFE up to 150000/mile 5 year protection.
On the back you have to read directions:
Step 1 Drain. Step 2 Flush. Step 3 Fill.
Recommended to ad 30% volume distilled water to 70% volume Antifreeze. If you flush the system and rinse with water you must add only 30% water to the antifreeze. There is more water trapped inside the engine compartment, because the thermostat is closed. Make sure to have a coolant density tester. When you finish one of 5 balls must sink, that indicates that you reached 50/50 strength. That means 50% Prestone and 50% Water, which will provide to your car a -34F degree FREEZE-UP Protection , and +265F degree BOILOVER protection. Make sure to open bleeding valve to discharge air pockets from the cooling system. Add coolant.The next day,while engine is cold open the radiator cap, and test the strength of coolant. If it is not quite right, then siphon coolant from the radiator and add antifreeze, or distilled water as necessary.
Let the car to cool down overnight and start engine. The cooling system might be cold. Untwist the coolant bleeding nipple. If there will be a jet or stream of coolant, that means the water pump is working and is O.K. After replace the thermostat. If still your car overheats then it might be a bad cylinder head gasket.

The dealer recommend GM Dex Cool Antifreeze.
But there are complaint against this type of coolant.
http://www.stevesnovasite.com/forums/archive/index.php/t-128547.html
In GM cars we replace Dex Cool with Prestone green coolant.
It's up to you. Ask before but if you decide to change the type of coolant then:
If your intention is to add coolant only, then you need:
Mix with
ANY COLOR ANTIFREEZE
ALL MAKES ALL MODELS
of cars and light trucks
add to ANY color antifreeze
PRESTONE
50/50
PREDILUTED ANTIFREEZE/COOLANT
EXTENDED LIFE up to 150000/mile 5 year protection.
DO NOT ADD WATER.

If your intention is to flush the RADIATOR (Cooling System), then you need:
Mix with
ANY COLOR ANTIFREEZE
ALL MAKES ALL MODELS
of cars and light trucks
add to ANY color antifrezze
PRESTONE
EXTENDED LIFE up to 150000/mile 5 year protection.
On the back you have to read directions:
Step 1 Drain. Step 2 Flush. Step 3 Fill.
Recommended to ad 30% to 50% volume, distilled water. If you flush the system and rinse with water you must add only 30% water to the antifreeze. There is more water trapped inside the engine compartment, because the thermostat is closed. Make sure to have a coolant density tester. When you finish one of 5 balls must sink, that indicates that you reached 50/50 strength. That means 50% Prestone and 50% Water, which will provide to your car a -34F degree FREEZE-UP Protection , and +265F degree BOILOVER protection.The next day,with a cooled engine open radiator cap, and test the strength of coolant. If not quite right, then siphon coolant from the radiator and add antifreeze, or distilled water as necessary.
Make sure to disposal the used coolant properly.

Audi cars use a special coolant called G12. It's not compatible with the typical green coolants you'll find at an auto parts store. You'll need to buy it at an Audi or VW dealership, or you can order it from www.germanautoparts.com, www.ecstuning.com, www.blauparts.com, or www.purems.com (I've bought from all four of these companies, and they're all top-notch). It's not terribly expensive, although it does run more than a typical coolant (I paid about $20 for a gallon of it at a dealership a few months ago).

FYI, the power steering fluid and the brake fluid in an Audi are also proprietary fluids, so if you go to order coolant, you may want to order a bottle of each of those as well to keep on hand.

VW/AUDI use a non ethylene glycol 50/50 mix of antifreeze/water into the expansion tank(the plastic bottle with the cap saying water or radiator fluid,(not all cars are marked).do not use standard antifreeze.

g 12 is the only antifreeze you should use in that engine