1.6 FSI Coolant system pressurising

[hydo14]

I posted this in the "Today I..." thread however have an unfortunate update

Today I entrusted my A2 fleet to the Pathfinder under 17s safe driving project and nervously let people learn to drive in a safe environment on a runway in Stafford. Turns out they are nicer to drive than the ex police diesel astras that are usually donated to the cause.

Okay so after two days of performing admirably with a new driver in the FSI, it was taken for a "spirited run" by one of the instructors before being used to demonstrate the increase in braking distance with speed and the FSI had a bit of a wobbly with the coolant system reporting low coolant - the coolant level was low in the expansion tank however the system was clearly pressurised which had pushed the level down. The car was allowed to cool and the expansion tank left open to hopefully drain any bubbles out that were in the system with the engine running, however during this when the thermostat opened the coolant system overflowed out of the top of the tank.

The car has been abandoned on the airfield until tomorrow, but my plan is to drain the coolant and replace it with fresh G13 as my working theory is that the coolant (which is of unknown age or service history) is more water than G13 and therefore is very close to the boiling point at the target 100-105 °C that the FSI's run at, with the extra load during this high speed driving I suspect that the system has boiled its coolant.

There appears to be no evidence of a head gasket failure as there's no steam/smoke from the exhaust or anything bubbling in the expansion tank. Is there anything that I also should consider?

 

[audifan]

The thermostat and the expansion tank cap.

 

[hydo14]

I will look at these tomorrow, the thermostat on these is electronically actuated is it not?
From memory the expansion tank cap is very clean and new looking (even the painted symbol is very vibrant)

 

[Andrew]

I will look at these tomorrow, the thermostat on these is electronically actuated is it not?
......)

I keep thinking about the detail of how the FSI thermostat functions, I don't think anybody knows, one day I will write a post when I understand it fully. From what I have researched the best answer I can give is yes/no, possibly sometimes.

I suggest you do a scan, it may well pick up a fault on the electronic actuation.

Andy

 

[spike]

Some general info on 'mapped. thermostats in this old thread - https://www.a2oc.net/community/inde...-which-thermostat-opens-fsi.19338/post-146592

Cheers Spike

 

[Andrew]

Some general info on 'mapped. thermostats in this old thread - https://www.a2oc.net/community/inde...-which-thermostat-opens-fsi.19338/post-146592

Cheers Spike

Thanks, link is the best I have seen and in line with my understanding.

Andy

 

[steaman]

You cannot run the engine at operating temperature with the expansion tank left open du to the temperature of 105 Celsius. ( ideal gas law: PV=nRT)
I learned this when the Cap had a broken gasket, it will overflow.

 

[PlasticMac]

You cannot run the engine at operating temperature with the expansion tank left open du to the temperature of 105 Celsius. ( ideal gas law: PV=nRT)
I learned this when the Cap had a broken gasket, it will overflow.

Cap off, coolant can't go over (about) 100C. It'll boil. Cap on, system pressurised, so boiling point is well over 100C.
I say about 100C, as the G13 raises the boiling point, but I dont know by how much.
Mac

 

[steaman]

Cap off, coolant can't go over (about) 100C. It'll boil. Cap on, system pressurised, so boiling point is well over 100C.
I say about 100C, as the G13 raises the boiling point, but I dont know by how much.
Mac

The operating temperature is up to 105C. When the Cap gasket were broken I could only drive a few kilometers before the coolant system needed a refill.

 

[Little Dog]

Pressure test it, use a hand pump and apply 1 bar. If the pressure drops you have a leak somewhere.

I don't know if this fits an A2 but this is the type of tool. I'll find out shorty, have one on order.

vidaXL 14 Piece Cooling System & Radiator Cap Pressure Tester Garage Equipment Tools Easy to Storage Car Enthusiasts Workshop Tool : Amazon.co.uk: Automotive

vidaXL 14 Piece Cooling System & Radiator Cap Pressure Tester Garage Equipment Tools Easy to Storage Car Enthusiasts Workshop Tool : Amazon.co.uk: Automotive

www.amazon.co.uk

 

[Andrew]

Cap off, coolant can't go over (about) 100C. It'll boil. Cap on, system pressurised, so boiling point is well over 100C.
I say about 100C, as the G13 raises the boiling point, but I dont know by how much.
Mac

The operating temperature is up to 105C. When the Cap gasket were broken I could only drive a few kilometers before the coolant system needed a refill.

Everything to me points at the FSI cooling system running at 110°C, most parts websites quote the FSI thermostat to operate at 109°C, which agrees with measuring blocks I have logged. At a guess/extrapolation the dreaded dash red thermometer overheat warning kicks in at 115°C.

Andy

 

[hydo14]

So after a coolant flush and replacement with G13 it ran fine for around 6 hours and then boiled again. Note that due to what the car is being used for this is particularly hard on the coolant systems as it involves a lot of slow speed manoeuvring and driving with the max speed typically being seen of around 15-20 mph hence the radiator and fan are having to work hard. The precise symptoms were a coolant level too low notification in the DIS and a temp reading on the dial of a little over 90. The system is not leaking out as the cap was hard to turn and then the system boiled over with coolant coming out of the relief on the back of the expansion tank when the cap was loosened. The level returned to normal after being allowed to cool down. I am now suspecting that the thermostat is a bit stuck in the close position which is causing an overheat situation within the engine.

 

[terrywindy1]

Had same problem with my Fsi after years of trying to find the fault. Car was OK on trips under 10 mile or so but pressure caused about 5 or 6 coolant hoses to split under the pressure. After a lot of other attempted fixs.Ended up replacing the engine .It was probably a crack in engine block, pressuring the coolant system Think it was caused by overheating from headgasket failure
One thing you could try is Evans waterless coolant. I have been using it in my replacement engine,so far so good

 

[steve54]

the fsi electronic thermostat defaults to fully open when when it stops working, full red DIS alert and cancelled on restart ,no coolant loss.
it did not reach full engine temp after that. this is just a guide to the electronic thermostat behaviour.

 

[hydo14]

This is all sounding rather terminal for my FSI. Hopefully it can limp on until the end of the week and then it looks like it's due an appointment with one of the breakers here, as I don't have the inclination to try and repair it when the car owes me nothing. It was unlikely to pass it's next MOT in October due to it also displaying the classic FSI BAD engine management light for a fault with the intake runner.

I might try an exhaust gas tester on the expansion tank to check if that's getting into the coolant system to at least maybe rule out pending catestrophic engine issues.

 

[audifan]

The water pump is working I take it?

 

[steaman]

Everything to me points at the FSI cooling system running at 110°C, most parts websites quote the FSI thermostat to operate at 109°C, which agrees with measuring blocks I have logged. At a guess/extrapolation the dreaded dash red thermometer overheat warning kicks in at 115°C.

Andy

If we assume that the 1.6 Fsi in VW Golf is the same as the one in A2 you will find a description of the Coolant system in SSP-296 ,page 10 and onwards.
There they mention 105 Celsius as operating temperature.

 

[PlasticMac]

The water pump is working I take it?

... and the fan?
Mac.

 

[PlasticMac]

If we assume that the 1.6 Fsi in VW Golf is the same as the one in A2 you will find a description of the Coolant system in SSP-296 ,page 10 and onwards.
There they mention 105 Celsius as operating temperature.

Could be that the FSI 'stat closes at 105C, and 'stat opens at 110C.
Mac.

 

[hydo14]

... and the fan?
Mac.

Yep the fan was working at the time. There appears to be coolant flow through the system but this was a noticeable flow in the small inlet at the top of the tank - this seems wrong to me, like there is a restriction somewhere in the coolant system, maybe the radiator is in effect being partially bypassed?

The car was used again yesterday but with the cabin heater on and the windows open. This did prevent the issue occurring however I had trust issues driving it 40 miles on the road when it was getting dark so called in some Audi assistance to get the car home and plan the next steps.