1.6 FSI Coolant loss

ornot

New Member
Good evening.

I'm hoping for some experienced A2OC forum member to help me work out what I need to do to repair my A2 before I simply end up slinging money at the problem.

The story:

On Friday my partner drove about 18 miles home from work, and about 10 miles in noticed steam coming from the engine compartment. When she got home she called me asking if she was alright to keep using the car, and I advised her to check the coolant. She told me that as she opened the cap some coolant sprayed out of a hole on the side, and I advised her to walk for the time being.

When I got home I found the coolant expansion vessel mostly empty (a good 3cm or so below the minimum marker), and also there was some coolant under the car and lots crusted around the seam on the expansion vessel. On Saturday I topped up the coolant and plugged in my ODB2 dongle so I could monitor the temperature, then ran the car at idle for 15-20 minutes. The temperature crept up on the dash, but lagged behind the coolant sensor, and when the coolant sensor reached about 95C the dash still only said 90, and the radiator fan did not start as I had expected it would. In this time the coolant level had not shifted, so perplexed I came to these forums and researched as much as I could and read about the dreaded head gasket failure.

A friendly neighbour came by and checked the oil for signs of head gasket failure, but the oil showed no sign of emulsion although it seemed rather low (but as my drive is on a slant it might just have all run to the rear). When I revved to 3k rpm there was a fair bit of water ejected from the exhaust, but it did not appear to be coolant. Running the engine on idle it slowly crept up to 105C but the coolant did not boil, nor spill. I recalled reading on the forum that the air con affected the radiator fan and when I turned it on the fan did spring to life. Throughout, the radiator did not appear to be getting very hot, but still no change in coolant level.

A quick top up with some oil and a brief drive on the roads, and while the coolant temperature edged up to 100C the coolant level did not change and no steam was observed. A longer Sunday drive of about 8 miles with careful monitoring of the coolant temp via ODB2, pushed the temperature up to 112C, at which point my partner swore she saw smoke/steam and I pulled over. Now a great puddle of coolant formed under the car, and looking into the engine bay coolant could be seen sloshing about in the under tray, and the coolant in the expansion vessel had dropped to about the same level as seen on Friday.

My diagnosis is that there is some crack in the expansion vessel that opens when it is hot, and dumps out all the coolant. But before I spring for a new expansion vessel, does anyone have any differential diagnoses?
 

Andrew

A2OC Donor
Hi,

A belated welcome.

I have a FSI and have experienced a death pipe problem, but first a word on coolant temperatures.

The dash gauge rarely tells the truth, once the engine has reached working temperature (after ~10 minutes) it is designed to show a constant 90℃, almost without regard to the actual temperature. Think of the dash gauge as a driver comfort gauge with its constant 90℃ indicating the temperature is within acceptable working range which varies continuously over quite a range. Apparently historically designed this way so the driver does not get obsseed/distracted by the varying temperature gauge. If the dash temperature goes above 90℃ is the time to get worried, the actual temperature will be in excess of 115℃(?), something is wrong.

The FSI coolant system is designed to run hot, indeed FSI thermostats come with an opening rating of 109℃, (apparently this aids combustion and is more efficient), so do not be alarmed if you monitor such figures but the loss of coolant is another matter.

Several candidates for the source of your leak; thermostat housing, coolant bottle/lid, other but the sudden onset and quantity of lost coolant make the death pipe the prime candidate. A death pipe leak is very difficult to verify with the pipe hidden behind the engine and direct observation essentially ruled out. All I can suggest is my experience, when the steam appears whip off the bonnet and see if whiffs of steam rise from the back of the engine.

Did it get so bad you got the big red flashing dash thermometer with scary dongs?

Andy
 

ornot

New Member
Thanks for the reply. No warning lights or error codes of any kind have appeared. And I stopped yesterday before I saw lots of steam. I certainly saw the coolant loss, so the fault took place. If I took off the under tray would I have any visibility of the death pipe?

I recall that a few years ago my partner broke down when a coolant leak stopped her dead on the side of the road. AA recovered her to a garage who invoiced us to repair a section of pipe, but the description is vague, and I never saw the car. If they replaced the death pipe then I would doubt that was the problem, (unless they effed it up, I suppose).
WOM replaced the water pump in March so I've messaged them to ask if they recall what it looked like back there (small chance after so long, but worth a punt).

The more I dwell on it the more likely it's a failed head gasket over-pressuring the coolant system. I'm going to ask around to try and find access to a pressure tester. But the thing has never been ragged (it was my mum's before it was my partner's and neither are racers), and only has 65k or so, so what could possibly have caused the head gasket to go?
 

Evripidis

Member
I have one suggestion in terms of money to be spent iff there are no apparent signs of head gasket failure:

1. Take everything out that is attached to the thermostat, i.e., the housing, the long pipe going to the pump (death pipe) and the thermostat itself.
2. If none of the above have been replaced in 10 years, put them in them bin regardless and buy new ones.
3. Before you put everything back on, inspect the hoses and connectors/couplers going to the expansion tank, throttle body, heater matrix and radiator. Should any even appear to be suspect get a new set or DIY yourself through with quality aftermarket hose and connectors.

If there has been a HG failure you'd probably have to add a step 0 in the list above.

Evros
 

ornot

New Member
WOM replaced the thermostat in March (I had quite a lot of work done in March), so it shouldn't be that. As for the rest of the pipework...

Ouch. That's more work than I have the facilities to carry out. If it needs more than hand tools I must resort to a garage. Additionally, we don't have a spare car to use while I pretend to have the skills.

How much damage can I conceivably do if I drive very carefully and keep the temperate low (I made it 6-8 miles yesterday and didn't go above 86C on the coolant sensor) assuming it's a head gasket issue? I'm running into transport issues otherwise.
 

Evripidis

Member
I see where you are coming from and I have only been able to do the work on the car because we have been able to use a second car (thankfully not an A2!).

If the thermostat had been replaced then some disturbance to the surrounding ageing plastics must have occurred if indeed you leak is down in that area.

Maybe get a telescopic inspection mirror and a really strong pocket flashlight, the type that you can focus the beam and have a good look. Something this drastic should be easily detectable. Are you able to remove the engine tray under the car so you can have a look?
 

ornot

New Member
I had planned to take off the undertrays to get a closer look; I can prop the A2 up on some bricks, and hope it won't fall on me! I'm not sure when though, and the time is rapidly approaching when I will need a second car.
Oh well. I need to get to work, and hopefully call a few garages to get a pressure test done.
 

Evripidis

Member
If you plan to take it to a garage for the pressure test then don't do any work under the car while it is on bricks. Best ask them to have a look when it is on the lift. It is only 10 screws to take the tray out. A lot better than getting flattened by a car!
 

kp 115

Member
Good evening.

I'm hoping for some experienced A2OC forum member to help me work out what I need to do to repair my A2 before I simply end up slinging money at the problem.

The story:

On Friday my partner drove about 18 miles home from work, and about 10 miles in noticed steam coming from the engine compartment. When she got home she called me asking if she was alright to keep using the car, and I advised her to check the coolant. She told me that as she opened the cap some coolant sprayed out of a hole on the side, and I advised her to walk for the time being.

When I got home I found the coolant expansion vessel mostly empty (a good 3cm or so below the minimum marker), and also there was some coolant under the car and lots crusted around the seam on the expansion vessel. On Saturday I topped up the coolant and plugged in my ODB2 dongle so I could monitor the temperature, then ran the car at idle for 15-20 minutes. The temperature crept up on the dash, but lagged behind the coolant sensor, and when the coolant sensor reached about 95C the dash still only said 90, and the radiator fan did not start as I had expected it would. In this time the coolant level had not shifted, so perplexed I came to these forums and researched as much as I could and read about the dreaded head gasket failure.

A friendly neighbour came by and checked the oil for signs of head gasket failure, but the oil showed no sign of emulsion although it seemed rather low (but as my drive is on a slant it might just have all run to the rear). When I revved to 3k rpm there was a fair bit of water ejected from the exhaust, but it did not appear to be coolant. Running the engine on idle it slowly crept up to 105C but the coolant did not boil, nor spill. I recalled reading on the forum that the air con affected the radiator fan and when I turned it on the fan did spring to life. Throughout, the radiator did not appear to be getting very hot, but still no change in coolant level.

A quick top up with some oil and a brief drive on the roads, and while the coolant temperature edged up to 100C the coolant level did not change and no steam was observed. A longer Sunday drive of about 8 miles with careful monitoring of the coolant temp via ODB2, pushed the temperature up to 112C, at which point my partner swore she saw smoke/steam and I pulled over. Now a great puddle of coolant formed under the car, and looking into the engine bay coolant could be seen sloshing about in the under tray, and the coolant in the expansion vessel had dropped to about the same level as seen on Friday.

My diagnosis is that there is some crack in the expansion vessel that opens when it is hot, and dumps out all the coolant. But before I spring for a new expansion vessel, does anyone have any differential diagnoses?
Hi Ornot ,
As the leak seems to be coming from the coolant expansion bottle area , I would start there as it also offers the cheapest fix
ie:
Purchase a new blue cap from Amazon (Febi) probably £8-10
Example: VAICO V10-0209 Cap, radiator https://www.amazon.co.uk/dp/B00DZFL3GM/ref=cm_sw_r_cp_api_glt_fabc_00S8BETC8W99441EGT60
New bottle £50?
All doable on a cool engine by you!
I would clean bottle & cap then place kitchen towel rolled up around the bottle to seeing you can identify extract area of leak.


Hope that helps
Keith.
 
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Exe_Chris

Member
Unfortunately, as my experience will attest, replacing one broken element of the cooling system will often push others closer to their demise. If one leak is plugged, pressure can increase through other vulnerable areas. I would always recommend anyone with an FSI to replace the death pipe at the same time as the thermostat housing, as if the housing is off anyway the pipe can be accessed and pulled out. When my car was leaking, it was the housing and not the death pipe that was failing, but it doesn't make sense to leave the old pipe there when it's easily (relatively) accessible.
My car has had the thermostat (coolant regulator) housing, death pipe, 'y-pipe' (coolant flange), coolant expansion bottle (plus cap), and the vent hose that connects to the bottle all replaced. Since then, coolant levels are good. DO NOT leave the original y-pipe in place. Evripidis has posted before regarding a suitable metal fixing, but even a replacement plastic one is strongly advisable. If you have a pair of plyers, and the ability to drain the coolant (partially), you can do this yourself. Even better, do it all at once.
All these things should probably be replaced every two timing belt services (unless they are replaced with metal pieces).
 

Andrew

A2OC Donor
DO NOT PUT THE CAR ON BRICKS UNLESS THIS IS YOUR CHOSEN METHOD OF SUICIDE.

I am not yet sharing your enthusiasm for a head gasket failure with which the coolant escapes into the cylinders is vaporised and is pushed out of the exhaust as steam, no pools of coolant.

I think the best course of action is to get the car to WOM, how, discuss with them. Personally I would risk driving there, I have RAC breakdown cover, I would be well equipped with water, towel to put over coolant tank and gloves. Partner monitors engine temperature and be prepared to stop, cool down and top up. I found that at fast speeds the natural ventilation was enough to keep an even coolant temperature, it was only in slow moving traffic that over heating occurred.

It is good you had no dash warning, but if you get the flashing red thermometer with scary dong, stop, matters are critical, but with temperature monitoring this point should never be reached.

Andy
 

PlasticMac

Member
Because of the dual cooling circuits, (unique to the FSI), which are separate from each other, with only the lower (cylinder block EGR etc) controlled by the thermostat, and the upper (cylinder head and heater matrix), circulating at all times, from cold, if the problem occurs when the engine is hot, perhaps the cause is in the bottom circuit, which doesn’t point to the cylinder head.
Mac.
 

steaman

Member
Because of the dual cooling circuits, (unique to the FSI), which are separate from each other, with only the lower (cylinder block EGR etc) controlled by the thermostat, and the upper (cylinder head and heater matrix), circulating at all times, from cold, if the problem occurs when the engine is hot, perhaps the cause is in the bottom circuit, which doesn’t point to the cylinder head.
Mac.

The cooling system is of a dual circuit design. This system features a separate coolant path, with different
temperatures, through the cylinder block and the cylinder head. The coolant flow is controlled by two
thermostats in the coolant distribution housing:
  1. One for the cylinder block (109° C) and
  2. one for the cylinder head ( 87° C).
 

PlasticMac

Member
The cooling system is of a dual circuit design. This system features a separate coolant path, with different
temperatures, through the cylinder block and the cylinder head. The coolant flow is controlled by two
thermostats in the coolant distribution housing:
  1. One for the cylinder block (109° C) and
  2. one for the cylinder head ( 87° C).
I thought there was only one thermostat, controlling the lower circuit with dual opening points, 110 for general driving and 87 for high speed driving. The lower temperature achieved with heater resistor in the wax stat. (This came from SSP222, which although it describes the FSI's "Electronically Mapped Coolant System" is not A2 specific).
Screenshot_20211110-180801.png

Where abouts is the second, 87 thermostat located?
Mac.
 

PlasticMac

Member
@PlasticMac

The thermostat on the FSI is singular and electronically controlled by the ECU. It does indeed have two opening temperatures. The normal 103 or so and the second by electrically heating the thermostat so that it opens about 87.

Found this BMW article that explains the electronic map cooling. Not identical to the A2 but the principle is identical...


@PlasticMac

The thermostat on the FSI is singular and electronically controlled by the ECU. It does indeed have two opening temperatures. The normal 103 or so and the second by electrically heating the thermostat so that it opens about 87.

Found this BMW article that explains the electronic map cooling. Not identical to the A2 but the principle is identical...

The Audi SSP 222 can be downloaded here
Mac.
 
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Andrew

A2OC Donor
Our A2 FSI does not employ a dual circuit coolant system as described in SSP296, but SSP222 is very much applicable. I am sat here with a thermostat housing (coolant regulator to give it its proper name) in my hand and there is only one thermostat.

1636573863509.jpeg


While not exactly the same, the design philosophy of the thermostat schematic that @PlasticMac posted above from SSP222 is very much evident.

The thermostat (with the large radiator return) bolts to the large aperture I have my little finger in, the two large pipes in the foreground are flow and return to the cabin heater exchanger, the flow is the one I have my thumb on. The large pipe just visible above the base of my thumb is the radiator flow. The little pipe above my thumb is the flow for the "ancillaries" with the corresponding return at the bottom right pointing at the chair under the heater return. The two (of three) bolt holes at the top leftish is where the housing bolts onto the block. The large pipe above the heater return with its two fingers pointing away next to the chair is the connection with the death pipe. The temperature sensor is out of shot at the top left just below the left bolt hole where it bolts onto the block. That's it!

It does marry up nicely with the standard FSI coolant system schematic.

FSI Cooling System Schematic.png

1 Coolant pump
2 Throttle valve
3 Heat exchanger for interior heater
4 Coolant expansion tank
5 Thermostat housing
6 Map-controlled engine cooling system thermostat
7 Coolant temperature sender G62
8 Radiator with outlet coolant temperature sender G83
9 Oil cooler
10 Cylinder head and cylinder block

I have yet to pin down the exact functioning of the thermostat and just today I ordered a used example with which I can experiment.

Andy
 
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Evripidis

Member
@Andrew

If you can come up with a simplified rendition then we can contact the manufacturer I found. He could make us up an aluminium version.

As it is, the weigh of the assembly is marginal to the bolt head surface holding it in place and it doesn't take a whole lot of science to verify that. You touch it and it feels ready to collapse.

Evros
 

PlasticMac

Member
Our A2 FSI does not employ a dual circuit coolant system as described in SSP296, but SSP222 is very much applicable. I am sat here with a thermostat housing (coolant regulator to give it its proper name) in my hand and there is only one thermostat.

View attachment 88154

While not exactly the same, the design philosophy of the thermostat schematic that @PlasticMac posted above from SSP222 is very much evident.

The thermostat (with the large radiator return) bolts to the large aperture I have my little finger in, the two large pipes in the foreground are flow and return to the cabin heater exchanger, the flow is the one I have my thumb on. The large pipe just visible above the base of my thumb is the radiator flow. The little pipe above my thumb is the flow for the "ancillaries" with the corresponding return at the bottom right pointing at the chair under the heater return. The two (of three) bolt holes at the top leftish is where the housing bolts onto the block. The large pipe above the heater return with its two fingers pointing away next to the chair is the connection with the death pipe. The temperature sensor is out of shot at the top left just below the left bolt hole where it bolts onto the block. That's it!

It does marry up nicely with the standard FSI coolant system schematic.

View attachment 88155

I have yet to pin down the exact functioning of the thermostat and just today I ordered a used example with which I can experiment.

Andy
A picture is worth a thousand words, (maybe two thousand of mine). Once you begin to understand how it works, any why, it is simply the way to create the best environment for the engine to run at maximum efficiency.
Mac.
 
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