Cooling system of doom

[shark_90]

OK, here's the situation:

I'm dripping a bit of coolant when the car's stood, don't know exactly where from but I will look when I can get it on a ramp.

The heater doesn't work (blows cold/not particularly warm at all but maybe a tiny bit of heat sometimes).

Car warms up quickly and generally sits up at 90 +1 or 2 notches.

The fan always, always cuts in when the car has been run whether I have been tanking it or not.

I am constantly topping up with water.

I've had a look through the forum and the concensus about the cooling system is to run the car up to temperature with the cap off and keep topping up the water until the fan has cut in once or twice? I have ****d around with this several times and with the cap off the car tends to boil over rather violently. This I don't understand.

Any ideas?

[Rusty]

If it's dripping water the get this sorted before spending too long bleeding the system. I've had leaking pipes from a badly fitting jubilee clip and another occasion where the jubilee clip had pinched the top hose and put a knick in it, had to cut the section off. This happened at Donington and there was water all over the rad!

This is how I bleed the system, had quite a bit of practice at this after my rad trouble last summer:-

• Fill the system and get the level somewhere close.
• Bleed the rad as best you can.
• Run it up to temp, topping up as you go.
• Close the cap and make sure the fan kicks in (I forgot to connect the fan on more than 1 occasion, no harm done though!).
• Let it cool (overnight normally).
• With the engine off:-
• Remove the 3 screws on the header tank.
• Lift it well above the rad.
• Remove the rad screw to let all the air out.
• Re-fit the header tank.
• With the car on level ground fill it up to the min marker.
• Repeat the header tank trick if necessary.
• Keep an eye on it for a run or two.
• Job Done

Hope you get it sorted.

[Knight Rider S4]

Has the car got Aircon?

Places to look for the leak :
Small pipe that runs from the thermostat to Heater matrix (sits under water manifold)
MFTS switch is always a bad one for leaking
Water pump
Water manifold

[Dpicariello]

I have a similar situation but I know exactly where my leak is coming from.

When i replaced the radiator I did the thermostat and I was massively paranoid about stripping the threads in the block. i therefore did them up just tight enough but that obviously wasn't enough.

Anyway, my advice would be to get the radiator out. It's a pig i know but with that out of the way you get amazing access to the majority of the cooling system. Inspect the hoses around the water pump and thermostat. It's also an opportunity to check the radiator.

Hope this helps,

Dan

[quattro20v]

When i replaced the radiator I did the thermostat and I was massively paranoid about stripping the threads in the block. i therefore did them up just tight enough but that obviously wasn't enough.

If i remember correctly, the torque of the bolts was something like 15nm, not much at all. Did you replace the o-ring with the thermostat?

[Fat Audi 80]

I hate to say it, but that sounds a bit like a Head Gasket failure to me. Are you sure you are not pressurising the water jacket with the cylinders? This will cause it to overheat quickly and boil over...

You can get a "sniff" test done at the garage to check.

HTH

Cheers,

Steve.

[Graham]

A car cooling system will boil over with the cap of, it relys on the build up of pressure to stop the coolant boiling. With the cap off, the water around the cylinder bore sleeves is heated to the point where it boils locally, creating steam bubbles in the head. As water expands to about 700 times its size when turning to steam, the steam in the head forces the water in the expansion bottle out as it is the only point of escape. If you close the system, the water wont boil as easily and the liquid level will remain constant pretty much (Hoses streatch and take up a bit.) (At 2 bar water will not boil till approx 120 Deg.C)
How i bleed the system is to fill the expansion bottle right to the very top-till it overflows, then undo the rad bleed screw and heater matrix bleed screw and keep on topping up till water comes out them both, once it does, seal them off.
Then using a hand vaccum pump suck out (Or syphon) the expansion bottle (Use a brake hose clamp to stop the radiator level falling by clamping the 6mm hose from the top of the rad to the expansion bottle) Then refil with coolant.
Job done.

[shark_90]

Cheers for the views and opinions guys - Graham, your explaination makes total sense and I will do that sometime today.

[BrianSmith_S2]

How i bleed the system is to fill the expansion bottle right to the very top-till it overflows, then undo the rad bleed screw and heater matrix bleed screw and keep on topping up till water comes out them both, once it does, seal them off.
Then using a hand vaccum pump suck out (Or syphon) the expansion bottle (Use a brake hose clamp to stop the radiator level falling by clamping the 6mm hose from the top of the rad to the expansion bottle) Then refil with coolant.
Job done.

Or, as i do is pour 4 litres of a good ethynol glycol antifreeze/inhibitor in first. with a small quantity of water the coolant should come up high on the expansion bottle. Run the engine for a couple of mins till the thermostat opens and the coolant level settles. I do this initially without the cap on so that the level can be topped up if necessary and also put leave the heater set on full heat - open circuit.

[shark_90]

Is there a way of knowing if the thermostat has opened or not without taking it out? I wonder if that's why my heater isn't working?

Oh and the little plastic screw on the heater matrix hose - just goes round and round. Better replace that hose as well then!

[Graham]

Is there a way of knowing if the thermostat has opened or not without taking it out? I wonder if that's why my heater isn't working?

Oh and the little plastic screw on the heater matrix hose - just goes round and round. Better replace that hose as well then!

The heater is not affected by the thermostat as it is fed directly from the block so it gives you hot air as soon as there is warm water, instead of you waiting for the thermostat to open freezing your whatsits off.

The thermo stat is quite easy to test in situ. Get thew levels right and bleed the system so the system can have full flow with no air pockets. Start up the engine and hold the pipe which comes out of the block behind/above the alternator infront of the main radiator (this pipe Tee's to feed the aux radiator and goes to the bottom front of the main radiator and comes out of the block on the thermostat housing).
as the engine runs there should be no heat in the pipe, when the gauge shows around 80-90 the pipe will all of a sudden get hot as the thermostat opens. (Wear a t-shirt as you dont want to get caught in the alternator belt--that would smart a tad)

If you have a leak, then as the system pressurises it squeezes water out, then when the car cools back to temperature the system is missing the water which was squeezed out, so now you have a slight vaccum--which sucks in air and the air promptly flows to the highest point, which if the leak is on the water manifold side ends up showing a loss of coolant in the expansion bottle.
But if the leak is either at the back, or the turbo side it flows up the heater matrix pipes and forms an air trap which stops nearly all flow through the matrix----When you rev the car does it give warm air breifly?? if this is the case then the leak is on the block/turbo side and an air trap is there. The quick revving just throws enough water around in the block to alow a small bit of hot water to leak past the air trap in the matrix pipe.
I have SFS silicone water pipes and it comes with a metal bleed on the matrix pipe which is mint--works every time, my old plastic one seized and sheared also

Graham

[shark_90]

Update on this one - I found the leak on the rad which turned out to be coming from the mounting at the bottom. The reason for this being that I was missing a metal bracket + mounting from the front which I didn't know was even meant to be there! Bought a new rad (£200!!) and new mountings and the missing bracket and stuck that lot in. Changed the hose to the heater matrix (the one with the bleed screw as mine sheared off) which was £40 (Audi ownership isn't cheap even with the older models).

Changed the water pump also, which had been making some rather bearing-crunching noises when cold.

Stuck a full bottle of G12 in. Undid the rad bleed screw and the heater matrix bleed screw, undid the three screws in the expansion tank and rested it on the ABS pump. Filled with water and listened to the blissful noise of air escaping from the system until water came out of both holes, did them up, topped it up and hey presto. Changed the thermostat while I had the car in bits too, which was knackered.

Heater now works, car doesn't run hot, and the cooling fan doesn't come on as much. Oh, I removed the aux rad while I was at it, and blocked the holes with 22mm plumbing bungs.

Sorted!

[Rusty]

Good work, that bottom bracket on the Rad went on my old NIssens one. 200 notes for a new rad is a bit steep, where was that from?

[S2central.net]

Another happy ending then - well done !

[Dingo]

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