[1.6 FSI] - Headgasket or simply Trigger's Broom

Hi Mac,

The car was idling for nearly 35 minutes and if left for any longer the coolant would start overflowing the tank. Obviously an abnormal situation.

The fan should kick but doesn't because as you say the temeprature at the outlet reads a continuous 16 degrees, so in the ECU's binary logic, all is good and it should keep the fan off.

But the hose is cold anyway and the sensor is not malfunctioning so something must be keeping the coolant in the block circuit stationary and not flowing as it should.

Or am I getting something wrong?

Evros
What was the temperature at the engine coolant outlet, after the 35 mins idling?
If less than 110 C, not overheating, (technically anyway).
Mac.
 
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Hi Mac,

It was a couple of degrees below 110 as my picture shows. A bit longer and it overflows, this is what I spent yesterday afternoon doing. I haven't left it to overflow today I just turned it off and quit.

What I am trying to say is that the temperature must eventually hit 110+ but the fan will never kick in. :confused:

Evros
 
I guess I should have left it overflow and then check with VCDS for anything abnormal. I might give it a try tomorrow.
 
I guess I should have left it overflow and then check with VCDS for anything abnormal. I might give it a try tomorrow.
I think the thermostat will/should open before the fan runs, the fan's logic is based on the temperature drop across the radiator, so, if the thermostat doesn't open, (because it's broken, or temperature is below 110C), then the fan will not run. But, it will run, if the ignition is off, and the engine outlet is over 110C. Only the FCM can switch the fan on. If your fan does not run, with the ignition off, the FCM doesn't think the engine is overheated.
I do think the total reliance on logic for cooling is a bit risky.
It's possible that the temp sensor on the engine outflow is reading low...
Does the temperature gauge in the dash show well over 90C. The other poster I mentioned where I'm sure the thermostat isn't opening, saw his rise towards 110C.
You can't test the thermostat out of the car, because you can't generate 110C C in boiling water!
Maybe put it in the oven, just to check it does open. Would rule it out, (or in).
Mac.
 
Hi Mac,

The sensor must be reading correct, since the lower hose was entirely cold.

Heck, from this afteroon I'd swear there is no flow through the radiator.

I suppose I can test it by boiling coolant in a pan rather than water !??

Evros
 
Hi Mac,

The sensor must be reading correct, since the lower hose was entirely cold.

Heck, from this afteroon I'd swear there is no flow through the radiator.

I suppose I can test it by boiling coolant in a pan rather than water !??

Evros
Coolant does have a higher boiling point than water, especially undiluted, but I don't know how high. Maybe hair dryer or heat gun? Bit risky with plastic parts though. Is the actual thermostat all metal? Just need to melt the wax. I'll watch with interest, and a degree of trepidation.
Mac.
 
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The thermostat is a metal part caged in a glassfibre plastic housing. I've taken it out at least 3 times but have not tested it in the usual manner.

I have a steinel temp controlled heatgun that can to 110 degrees pretty accurately but in all honesty I haven't got the willpower to take it all out again.

I'd rather replace it but then I'd have to find a parts source willing to ship it.
 
The thermostat is a metal part caged in a glassfibre plastic housing. I've taken it out at least 3 times but have not tested it in the usual manner.

I have a steinel temp controlled heatgun that can to 110 degrees pretty accurately but in all honesty I haven't got the willpower to take it all out again.

I'd rather replace it but then I'd have to find a parts source willing to ship it.
If it helps, I can source it in UK, then post to you. I think it best to use genuine. I'd start with @CreweAudi
You could risk a used one from our club breakers, @Clackers , @A2Steve , or @Ami and check it before fitting.
Mac.
 
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Thanks for offering Mac. I've been there before with Steve and a forwarder for small parcels that took care of VAT/customs/etc. and it was a breeze to work with. Unfortunately they seized their operations in the UK so sending anything by post ends up costing a small fortune. It is going to have to be an EU-sourced part I am afraid. I do not want to set foot in the customs office again, a complete nightmare.
 
Thanks for offering Mac. I've been there before with Steve and a forwarder for small parcels that took care of VAT/customs/etc. and it was a breeze to work with. Unfortunately they seized their operations in the UK so sending anything by post ends up costing a small fortune. It is going to have to be an EU-sourced part I am afraid. I do not want to set foot in the customs office again, a complete nightmare.
😕 Mac.
 
Good Evening Evros,

I have have been doing non car stuff for most of the day and only just catching up, interesting but no end result.

I have read today's posts and from a temperature point of view nothing is wrong, except I would have expected the engine outlet temperature to reach 110℃ well before the 35 minutes. Everything fits, flow through radiator only occurs when the thermostat is open which never happens because 110℃ has not yet been reached, and hence the static low radiator sensor outlet temperature.

Some thoughts.

1. I would experiment and drip boiling water on the hose adjacent to the radiator outlet sensor or use hair dryer and see if the sensor responds. I think there should be no need to start the engine.

2. On testing the thermostat out of the car. Something I have been meaning to to do (I have a used spare genuine thermostat) but never got round to it like many things. As said no use using water and coolant might not be enough (I think pressure comes into play as well) so I thought of using diesel oil. Diesel oil has a boiling point way in excess of what's needed and by all accounts not very flammable, but of course outside with safety precautions.

It focuses the mind wonderfully when you realise the genuine Audi thermostat is about £100, but much cheaper aftermarket options are available. On this I have firm belief the genuine Audi thermostat is made by Mahle.

3. If you can wait until Monday evening I will monitor the temperature groups and post so you have some kind of reference. Worth doing any way to put on the forum for others in the future.

But of course none of this addresses the problem of the overflowing coolant tank.

Andy
 
Thanks for your response Andy. Much appreciated. Excellent input.

The one I have fitted on it now is a mahle with the vw emblem ground off. So yes. I fitted an oem part. I think that I posted my finding on here ages ago.

Evros
 
Hi all,

I've just gone through another round of tests:

0. Topped up the coolant.
1. Let the car warm, up, taken it for a short drive (mountainous, 15 minutes), came back. Signs of coolant overflow at the tank. The lower hose did become warm which is good, me thinks.
2. Parked it, let it idle and hooked up VCDS.
3. The blocks 130, 131, 132 all checked out, i.e.,:
A. When the engine temp goes above the specified 110 (e.g >120) the thermostat will load up and the temperature will drop to normal levels (<110) after a while. This is all with some hysteresis, i.e., the condition in the group 131 must be met for some time for the thermostat element to start loading.
B. When the radiator temperature hits 99 or there about which is 10 more than the specified 89 then the fan will kick in, again with some hysteresis.
4. Wiped up the coolant overflow, put the bonnet back on and went for another drive, highway this time,. 10 minutes.
5. Came back, bonnet off, no overflow.
6. Left it idling, hooked up vcds, all normal same as before, thermostat and fans cycle as they should (!?).

What do you guys think, blocked rad or insufficient fan?

Evros
 
Hi all,

I've just gone through another round of tests:

0. Topped up the coolant.
1. Let the car warm, up, taken it for a short drive (mountainous, 15 minutes), came back. Signs of coolant overflow at the tank. The lower hose did become warm which is good, me thinks.
2. Parked it, let it idle and hooked up VCDS.
3. The blocks 130, 131, 132 all checked out, i.e.,:
A. When the engine temp goes above the specified 110 (e.g >120) the thermostat will load up and the temperature will drop to normal levels (<110) after a while. This is all with some hysteresis, i.e., the condition in the group 131 must be met for some time for the thermostat element to start loading.
B. When the radiator temperature hits 99 or there about which is 10 more than the specified 89 then the fan will kick in, again with some hysteresis.
4. Wiped up the coolant overflow, put the bonnet back on and went for another drive, highway this time,. 10 minutes.
5. Came back, bonnet off, no overflow.
6. Left it idling, hooked up vcds, all normal same as before, thermostat and fans cycle as they should (!?).

What do you guys think, blocked rad or insufficient fan?

Evros
You Probably have done this/silly question when topping up from called & letting it warm up did you have the heater on with bottle cap open to let air bubbles out until water started to boil, before putting cap back on, just a thought. to avoid airlock in the heating/rad system.
 
Where do you see the signs of coolant overflow exactly?
You mention the temperatures of 89C, in fan control, I think the fan is only going to run if the temperature drop across the radiator is too low, (this seems to be some algorithm rather than a set figure), usually, when driving, air flow through the radiator will be enough without the fan. Idling, when stationary, and a warm engine is more likely to give insufficient drop across the radiator.
I can't explain why, but my feeling is that the cooling system is OK, and coolant loss is not temperature related.
The suggestion by @Ami of air in the circuit is a distinct possibility. Is there anyway air can get in, when the car is parked, and cooling I wonder? It shouldn't, I know, rather coolant will be drawn in from the reservoir. But for this to happen, the cap has to open to release the vacuum ... just trying find an alternative to an engine cooling system at fault.
I think we may be surprised by how effective the small, (head, oil cooler, and heater matrix), cooling circuit is. Andrew's log should be very informative 🤞.
Incidentally, Audi define an FSI engine as "warm" between 85 and 110C! No mention of hot ...
Mac.
Edit: Above, I suggest that "the cooling system is OK" I mean the controls of the cooling system, thermostat fan, sensor etc are OK. There obviously is a problem with the cooling system, which may be plumbing, not control.
Mac.
 
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Hi Ami, Mac,

I have taken all measures to avoid air locks so far and hopefully I succeed. Especially after yesterday.

There have been measurements of 125 degrees and I am wondering if the coolant that I am using is insufficient. I am using a premix mannol g12+ which the best I can get over here

The cooling system and its closed loop control seems to be working as it should. The overflow I am experiencing is at the vent hole on the tank. I have a new one to be fitting which is easy enough. I got a polo one which appears to be identical bar the mounting points. This could be drawing in air or the opposite, if there is a crack in it or something.
 
@Ami I am thinking that if the expansion tank has failed internally then maybe it is drawing in air when cooling down. I'd be happied if the sniffer gave me a positive result. At least I'd be done with it and start stripping.
 
Where is the one way valve, that allows air into the expansion tank, so that coolant can be drawn into the system as it cools and contracts?
My thinking is that the valve is not allowing air into the expansion tank, causing air to be drawn in somewhere else.
I'm guessing that the expansion tank cap is that valve.
Or is my idea of how it works totally wrong?
Mac.
 
@PlasticMac I have a spare tank that I can pressurise and a vacuum pump with a set of ac gauges to test cap. I'll waste my time fitting the brand new polo one instead though as it will prove quicker. Most of my hoses are custom made so maybe there is a slight orifice somewhere that only leaks under vacuum.
 
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