A4 tdi Coolant Expansion *Help*.

[Ianh1]

I have a 98 A4 1.9 tdi 110 130k with a coolant problem, It appears that when driven hard or at high revs the coolent is being forced out thtrough the expansion bottle overflow pipe, resulting in a low coolent level every few days.
The temperature gauge sits perfectly at 90 deg. the engine runs as smoothly as it did before this started to occur. it starts first turn. there is no evidence of head gasket problems i.e oil is water free and coolant does not have any tell tail signs like the oil like film or oily/deisel smell and no white smoke or water from the exhaust.

The radiator feels cold even after a few mile run when the coolent is expanding.

I have an idea it may be the thermostat failing to open however I would have thought that would have caused the engine temperature gauge to go up.

Any thougths from anyone would be welcomed, before I get the spanners out

[Teutonic_Tamer]

Hi, and welcome to the forum.

It could be whole number of issues - is the expansion bottle pressure cap in good condition and releasing at the correct pressure, do you have any "soggy" hoses which might be balooning under pressure, are you sure your temperature sender is OK, does the heater inside the car get nice and hot, are you getting a proper flow of coolant through the radiator, have you mixed incompatible antifreeze aditives??????.

Start the car from cold & let it idle. After a short while, the temp guage should rise progressively, but the top hose to the rad will remain cold until gauge reaches normal temp. When it does reach normal temp, the top hose to the rad will sudenly get hot as the thermostat opens. Leave it on idle for a while longer, and the heat should eventually reach the rad bottom hose.

KEEP YOUR HANDS/SCARF/TIE/SMALL CHILDREN/ANIMALS AWAY FROM MOVING PARTS.

Let us know how you get on, Rgds

[auiron]

Hi Ianh1, It is possible that the plastic hose adaptor that sits over the thermostat has cracked ( temp. sensor attached ). This is common on some vehicles.

All the best, hope you solve the problem.

[Ianh1]

Thanks Tautonic Tamer and Auiron, I will take a look at it tonight after she who must be obayed gets home from work and it has had time to cool down, (the car that is) I'll let you know how it goes. Thank again.

[Dave Avant]

I would say expansion tank cap if no leaks present anywhere else.

The boiling point of water under pressure is higher than a vented system.

If the cap has failed the pressure isn't kept up, the water expands and overflows out of the expansion tank ultimatly reducing the volume of water thus the frequent top ups. It will boil over but the actual temp won't be any/much higher than normal.

After a run or when it overflows the rad can still be cold as it actually hasn't got too hot or hot enough to use the radiator, its just the cap letting the water out and not pressurising the cooling system. The thermostat opens at near boiling point temp. Change the cap and see how it goes.

[Ianh1]

Hi Folks,

Well I did what Teutonic Tamer suggested and it went as it should , the gauge rose gradually to 90deg the top hose went hot followed shortly after by the bottom hose, and the haeter was nice and hot so I gather the thermostat is working ok. I did notice that there was a bit of a scale deposit built up on the inside of the bottle neck which I have cleaned off as I thought this may be affecting the seal, it was still forcing water out of the o/f pipe but only in drips. There does not appear to be any balloning of pipes or anything obvious, I have not gone as far as the thermostat housing as the car was hot and the rain and wind took second place to a few glasses of wine. so I think I will take Dave Avants advice and start with the easy option of a new filler cap.
I will let you know if it cures the problem.
Many thanks to all.

[Dave Avant]

Where is the overflow pipe, is it from the filler neck? Mine doesn't have any overflow pipes. They usually have a small pipe going into the top of the tank which is the expanded hot water and a thicker pipe out of the bottom which lets water into the system if needed. The water when hot should circulate through the expansion tank. If its leaking at the pipe, try a new clip to seal it.

Can you take a pic and say where its coming from?

You can have the system pressurised to test for leaks and the cap tested at dealers.

[Ianh1]

Hi Dave,

The expansion tank is double lined the inner is the expansion vessle and the outer is where the expanded water overflows into. there is a small pipe on the top which is the expansion pipe and a larger pipe at the bottom I think, (I am doing this from memory as I don't have the car here to look at) the run off pipe for the outer is on the bottom of the bottle and take the expelled water straight through the engine bay to below the vehicle and thats where the water is going. it can only get there via the filler cap so I will try a new one.

Cheers.

[Dave Avant]

I'll have a look at mine too, just to see, but from what I remembered it was a standard bigger pipe out of bottom and smaller pipe usually from the engine head or thermostat or rad.

[Teutonic_Tamer]

Ianh1 is correct.

When you remove the pressure cap from the expansion vessel, there is (obviously) the centre hole for filling the coolant, then, working outwards from the centre of the filling hole, there is the threadded boss which the cap screws onto, then, there is a gully, which is the overflow, and then finally the outer case of the expansion vessle.

The overflow gully is connected to a pipe inside the vessle (but sealed from the main contents of the vessle), which exits at the bottom of the expansion vessle. The VWs usually have a round or spherical shaped vessle and you cant really see the expansion pipe, or where it exits - but if you feel underneath, you should find it. On the larger Audis they have a rectangular shaped expansion vessle, and it is quite easy to see the pipe.

Rgds