Coolant replacement

C

Chiefmechanic

Active Member
I have to change my coolant radiator as the plastic tank at the end has cracked and leaks under pressure. Taking the front bumper off was a pita. How difficult is it to purge air from the coolant system when I go to refill it. Is there any tips for this procedure.
Thanks, Brian
 
Chiefmechanic said:
I have to change my coolant radiator as the plastic tank at the end has cracked and leaks under pressure. Taking the front bumper off was a pita. How difficult is it to purge air from the coolant system when I go to refill it. Is there any tips for this procedure.
Thanks, Brian
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I haver always managed to bleed the system by just leaving off the filler cap and running the car up to heat by leaving it to tickover with a few pulses of the throttle every now and then.

Never had to make use of any bleed nipples etc.


Steve B
 
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I'm assuming you know where the plastic bleed hex screws(tdi?) , one above the engine for the cabin heater and one bottom / front right of the engine, loosen the lower screw first, fill the expansion tank with

coolant and start squeezing coolant hoses ( mainley the top and bottom rad hoses), keep topping the expansion tank untill you see coolant leaking from the lower bleed screw, secure the lower bleed screw and

start the car and set cabin heaters to max, loosen the top bleed screw, seeing coolant leaking may take a couple of seconds and secure top bleed screw.

run engine untill rad fan kicks in as well as checking for leaks / topping up coolant

( when i replaced the coolant on my car last aug, i had to rev it a few time untill the fan kick in at 98 degrees c via vcds which took 30-45 mins )
 
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Radiator changed but the heater matrix will not warm up. I checked the flow when I flushed out the system prior to fitting the new main radiator so I know it’s not blocked. Bled the pipes and cold coolant comes out from the heater matrix even though the rest of the system is up to temperature. Any ideas what would cause no flow through the heater matrix. Only cold air inside the car.
The electric fan comes on as soon as I start the engine from cold. This can’t be right. Are the faults connected or separate.
Brian.
 
It is likely to be an air lock.
If the coolant flow from it is cold and the engine is hot then it must have an air lock.

Have you run the car without the filler cap on it. That should allow the air to escape.

Steve B
 
Chiefmechanic said:
Radiator changed but the heater matrix will not warm up. I checked the flow when I flushed out the system prior to fitting the new main radiator so I know it’s not blocked. Bled the pipes and cold coolant comes out from the heater matrix even though the rest of the system is up to temperature. Any ideas what would cause no flow through the heater matrix. Only cold air inside the car.
The electric fan comes on as soon as I start the engine from cold. This can’t be right. Are the faults connected or separate.
Brian.
Click to expand...
Also the coolant fan comes on when the air con is on so it is probably not a fault. It is meant to run constantly when the air con is operating.

Steve B
 
Make sure that you have the heater on full as well to ensure that the maximum flow settings are used an allows the coolant to flow.
 
Catnip64 said:
Note that you don't need to have the climate on hot (or even switched on) to get the water flowing through the matrix.
Here's the official process for filling the system: http://workshop-manuals.com/audi/a2...g_system/draining_and_filling_cooling_system/

Steve
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That's something I have always been told to do, maybe just an old wife's tale (or old mechanics tale).

Have looked at the link for refilling the system I don't have the snazzy pump etc. and I need to do mine soon when I do the cambelt change. Was thinking of just pouring in the mixture slowly and letting air escape naturally before starting the engine and allowing it to run with the expansion bottle cap off thus allowing air to escape.
 
Switching the heater on full blast were old mechanics words of wisdom and were relative because the controls operated a valve which switched the water flow through the heater core on and off. It was easy to get an airlock in the system if the procedure was not followed

In modern systems the water flows through the heater core (which is no longer in the cabin) all the time and cabin temp is controlled by the fan blasting air through the heater core. Changing the heater controls no longer affects the coolant flow through the heater

Cheers Spike
 
spike said:
Switching the heater on full blast were old mechanics words of wisdom and were relative because the controls operated a valve which switched the water flow through the heater core on and off. It was easy to get an airlock in the system if the procedure was not followed

In modern systems the water flows through the heater core (which is no longer in the cabin) all the time and cabin temp is controlled by the fan blasting air through the heater core. Changing the heater controls no longer affects the coolant flow through the heater

Cheers Spike
Click to expand...

Thanks Spike. The old way of the heater working was the way I thought they still worked as I have never had to strip a heater out but always followed the method of having the heater on hot and full when bleeding a cooling system.

It is always good to learn :)
 
Thanks for all the replies. I have run the engine up to temperature with the cap off squeezing pipes till my hands cramp and it seems to me that the thermostat is not opening. The bottom hose for the main radiator never heats up. I have looked at my parts diagram and can’t find a thermostat. There is a temperature control housing. Can I buy a thermostat or do I need the housing.
Brian.
 
People often replace the housing at the same time as the thermostat, mainly because they can become brittle and damage easily.

But there is no real reason to replace the housing unless it is broken or damaged.

The thermostat on the FSI is a special one and so check it out first (At least visually once it is out) before buying a new one.

Steve B
 
Bought one that was supposed to be correct but is totally different. Real pain to get out as the gear selection linkage has to be taken apart. Not looking forward to resetting it. Does the 1.4 and 1.6 fsi share the same thermostat
Brian
 
My specialist area is the TDI but I always thought that the thermostat on a FSI was on the opposite end of the engine to the gearchange!

But I have never changed an FSI thermostat, so I am almost certainly wring then.

But I am pretty sure that the 1.4 has a different thermostat, as I have mentioned the 1.6 has a special one (electrically operated I believe)

Steve B
 
The saga continues. I have poured a kettle of boiling water over the thermostat with no movement at all. The thermostat is rated at 109 degrees C but I would have thought I would get some movement. I have driven the car around town and the temperature gauge hits 90 C pretty quickly but the bottom radiator pipe and the interior heater matrix never warms up.
Does anyone have a scrap 1.6 fsi engine that would sell me the thermostat. Brian
 
Did you have full fluid movement before through the bottom pipe?

Sometimes if there is crap in the system then emptying and refilling it can move it around the system and cause small blockages.

I had it once with a large engine BMW and the head gasket went. I did it all myself and cleaned the water jacket on the engine but thought there was a secondary drain plug on the block as I had removed the one I knew about. My finger would go slightly in the hole but then hit the back of the compartment, or so I thought until I realised that it should have been deeper. I used a small alan key in the hole and gave it a tap with a hammer. As soon as I did this, the material that had solidified (radweld or something I think) broke up and then the water I had put in the system to flush it came flowing out of the hole. I cleaned it and flushed it through thoroughly and put it back together with no issue. If I had not have noticed this blockage then it would have ended up with overheating and more problems.
 
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