View Full Version : Occasional large coolant loss

26-10-2009, 12:34 PM
Friend bought P-reg A4 AFN, about 110k miles, a couple of months ago. Engine bay amazingly clean, couldn't see anything wrong with it, drives well. About once every 3 weeks it blows about a litre of brown coolant out through the expansion tank stub pipe and low coolant light comes on.

1/ she says she not seen the temp go high,
2/ she has driven 100 mile journeys with no probs
3/ water loss happens around town
4/ I have not seen the oil temp gauge rise off its stop.
5/ there is slight brown sludge on inside of coolant filler cap
6/ she says it is hard to start the day after a coolant loss

I ran a test the other day and got these codes:
VAG-COM Version: Release 409.1-US
Control Module Part Number: 028 906 021 CE
Component and/or Version: 1.9l R4 EDC 00SG 0803
Software Coding: 00002
Work Shop Code: WSC 06335
2 Faults Found:
00550 - Start of Injection Regulation
17-10 - Control Difference - Intermittent
17978 - Shareware Version. To Decode all DTCs
P1570 - 35-10 - Please Register/Activate - Intermittent

I'm not sure that the viscous fan coupling is working properly and I have never seen the electric fan kick in. Probably more than one fault here but where do you suggest I start?

Thanks in advance. OD

06-11-2009, 01:52 PM
I would say it has nothing to do with the viscous fan. I have driven 1.9 tdi a4 without a viscous fan at all for over half a year. Sitting in trafic at below 30 degrees outside temperature will do nothing to that engine. It has a huge radiator and it's a very efficient diesel.
Your error codes are related to your boost pressure control, should not have anything to do with that.
I am sure there is another detail your friend haven't noticed about the behaviour.
Could be a head gasket issue....
It is worth checking the water pump and thermostat.

06-11-2009, 09:44 PM
Theory: Your thermostat is closing while the motor is too hot, pushing that pressurized coolant out through the tank. Sign of a failing thermostat?

And should coolant be orange? Sounds like she needs a coolant flush is needed...

17-03-2010, 01:36 PM
Thanks guys. We still haven't sorted the problem, but yesterday I had a look under the bonnet and examined the expansion tank filler cap, since that was permitting the water to come out. Completely different from my Passat AAZ or Sharan AHU of course. It looked tired and O-ring was tatty so I bought a replacement.
#I then left engine running for 40 mins and system pressurised, tell-tale was squirting nicely but temp gauges (oil & water) stayed at left hand end and internal heater wasn't giving out much heat, in fact top rad hose was only warm. Viscous fan spinning but could stop it with gloved hand. Electric fan static.
#I then went for 2 mile drive on flattish road to shop, temp gauges stayed at left hand end.
#After 30 mins in shop I came out and took car for run at 60 mph up long hill - 2 miles or so - still gauge needles unmoved.
#at top of hill turned left and slowed down to go through underpass and within 30 secs water temp had shot to 90 and "thermometer light" came on with beeps. Cabin heater started putting out hot air.
#Pulled up at roadside expecting big puddle under car but after about 20 secs light went out, beeps stopped, and water temp gauge slowly went back to left hand end. Cabin air cooled.
#carefully set off home and managed another three miles downhill and flat without incident until temp and beeps came back again at a roundabout.
#on arriving back at house, checked exp tank - no obvious change in tank water level.Viscous fan spinning but could still stop it with gloved hand. Electric fan still static.
#fuel tank & voltage guages working fine, oil temp never moves.

I'm going to collect car and put it in my garage. I'm suspecting air pockets, thermostat, water pump, temp sensors. Yes there is some grey gunge in oil filler cap now but I'd like to find out what the underlying cause of the problem is before "just" replacing the head gasket. I have read the other recent posts.
#This 97 120k miles A4 has the AFN engine but is rear wheel drive - came as a shock when I looked under the bonnet for the first time - I thought all cars since the Vanwall were front wheel drive.

All clues and experiences invited!

17-03-2010, 01:49 PM
There is no such thing as a rear wheel drive VW Passat,you have a 4 motion vehicle.The best way to determine head gasket failure is to really press the engine and feel the top and bottom radiator hoses,if both are very hard,the problem is the head gasket,which may not,cause the engine to overheat under normal driving conditions,i have seen this a few times

17-03-2010, 09:03 PM
I'm pleased with the way the nuts are coming off easily - for a P reg. First thing I looked at was the thermostat, just needed to swing a strengthening strut out of the way and then 2 Allen-headed nuts got me in.
It looks a bit - erm - odd. See pic.

17-03-2010, 09:08 PM
Sorry - can't seem to upload more than one pic per post. I'm thinking that may some of the missing bits may have fallen apart and damaged the water pump - even though the tell-tale is squirting into the expansion tank OK - so I have looked and seen that the water pump W seems to have the hydraulic pump H grafted on to it. Do they come off together or separately? T is the thermostat housing...

Hayne's isn't clear on this point.Thanks

17-03-2010, 09:18 PM
And finally for now, it seems I need to pull the "lock carrier" at the front out to a "servicing position" by removing the bumper and undoing what sounds like every darned bolt near the front end to get at the water pump. Is this necessary? radiator is brand new 2 months ago, by the way.

Again, thanks for any advice. On the thermostat topic, has anyone seen one fail like this before? Do you think a cowboy has modified it to improve cooling? If so why not just remove it? Baffled here...

17-03-2010, 10:24 PM
Ok, service position isn't that bad. Don't remove the radiator etc, you can remove just the core support and angle the assembly out of the way without disconnecting the AC lines. From there the water pump is easy to get to, and yes, necessary to do the job right.

You might want to flush the block and radiator to get the debris out from the thermostat. And no, I don't think someone in their right mind would modify it like that!! Perhaps bits from your waterpump tore through it? I don't know?!?! I'd start with a new waterpump and thermostat.

17-03-2010, 11:06 PM
Thanks for that advice. I'll get on with it and let you all know how things proceed. OD

18-03-2010, 11:46 AM
Let me guess. You'll find the pump impellor damaged. So someone knocked the guts out of the thermostat as a workaround (even the AA will resort to this to get someone home if their thermostat fails). The lack of forced circulation creating the geyser effect.

19-03-2010, 05:30 PM
Ike - no cigar I'm afraid. Living out in the sticks I bought a new water pump and thermostat while trying to find a place that sold "T47" torx bits to allow me to "slide the lock carrier to the servicing position". 8 words, took 4 hours to do it. US websites said T47, local tool distributors said 40, 45 or 50. Anyway, a T45 on a 1/2" socket did the job.

Today I finally got the water pump off only to find no signs of wear - smooth running, and I am tempted to put the old one back on.

Lack of thermostat internals explains the non-recording temperature but I am still left with a car that will sit ticking over for 40 mins, then go up a 2 mile long hill without a problem at 2000 rpm, no temp indicated, and then suddenly get a "back to life " water temp gauge, water temp warning light and buzzer 30 secs after coming off the dual carriageway. Which then after 10 or 15 secs all went out again and temp gauge went back to its cold position.

Any other ideas, folks, or is it really the head gasket (minimum)? Thanks OD

19-03-2010, 05:33 PM
Coolant temperature sensor?

19-03-2010, 05:40 PM
That was quick Chris - and thanks, I was just putting my boiler suit back on to go check the sensors- I see one in the radiator which I suspect turns on the electric fan - plus maybe other things - and another single sensor - blue I think - up at the top back of the engine with 4 pins. I have AHU and AAZ engined cars out there on the lawn but I bet the sensor will be different from theirs.

More later. Cheers, OD

19-03-2010, 06:02 PM
No problem. You are probably going to need to replace the blue one. They are VIN specific so be wary if you get it locally.

The one in the radiator is indeed a fan switch.

19-03-2010, 06:47 PM
Yes, faulty sensor fits - but why does it periodically vent? hmmm

19-03-2010, 07:54 PM
Still working on it. Decided to put new pump on even though old one seemed ok. Needed new seal anyway. My regular garage engineer suggests an airlock in the system - some hot parts not getting water and then they do and the water instantly flashes to steam. I have read somewhere that one needs to be very throrough about purging the cooling system on this model. More later. Thanks everybody. OD

19-03-2010, 09:54 PM
Car is back together except for the "lock carrier in the service position" and I filled it up, finally with a funnel going into the cabin heater matrix until water came out of the matrix stub. It has run for 30 mins in garage, bit of fiddling with the blue temperature sensor got the dashboard temp gauge working and it eventually went to 90 but I couldn't get it any higher so will have to put front back on tomorrow and take it for a run. I don't know if all of the blue sensor is working or just the half that talks to the dashboard.

More tomorrow and thanks again for the help. Great forum. :beerchug:


20-03-2010, 03:45 PM
Test drive Saturday. Before setting off I found instructions on the net for bleeding the air from the cooling system: remove 3 screws holding expansion tank to car, raise tank (actually hung it on stiff wire from bonnet catch), unclip left heater hose and wiggle off until little hole in wall of tube is off the stub. Got air out of matrix, replaced hose and clip, then saw stream of bubbles coming out of tell-tale pipe into expansion tank.

Left engine running for 15 mins, didn't get to operating temp or blow out water so took it for drive. After 2 miles gauge temp up to 90 but t/stat hadn't opened, radiator cold, so went for a further 3 miles on up & down country lanes. Slowing at top of hill got 3 beeps and thermometer warning symbol came on but gauge temp was still 90. Looked under bonnet with engine still running. Hoses hard, matrix hoses hot, radiator barely warm, exp tank level about 30mm above bottom. I gently released the exp tank cap and the water level came back up again. I guess the hoses had just expanded with the pressure, causing the tank level to drop. Warning light went out. Drove on for another couple of 2 mile stretches, warning came on, released pressure, level came back up and returned home without needing to add any more water but had lost maybe 1/2 litre over the 9 or 10 miles.

Can it now be anything but a head skim & gasket job?

29-03-2010, 01:32 PM
How are you getting on with this? Your experiences are similar to mine; my thread is here: http://www.vwaudiforum.co.uk/forum/showthread.php?t=91347

29-03-2010, 01:54 PM
I managed to find some lengths of studded rod from b&q which I screwed into one lock carrier retaining screw hole on each side of the car and was then able to wiggle the front end out about 10 inches - enough to get at the bolts which hold the viscous fan blade ring to its hub. From recollection they were tricky because they needed a 10mm socket that was really skinny. After that I could get to the 5? bolts holding the water pump on.

No problems, replaced pump even though original was looking fine, replaced t/stat, filled up expansion tank (removed from mounts and suspended on wire from bonnet to ease the purging) and put it all back together. Saw continuous stream of bubbles coming into exp tank from tell-tale pipe while it was hanging up.

Temperature eventually rose to 90 and stayed there, system pressurised although didn't blow off, probably due to new coolant filler cap. Level in exp tank did go down due to pressure causing the hoses to bloat. Took exp cap off and put old one back on minus its O-ring. Can now drive car gently on flattish roads without losing too much coolant as it doesn't pressurise.

It is however booked in at my garage for what is almost certainly a gasket and head skim, or new head, or block. I'll let you know what it needed when it has been fixed. I told the garage I didn't want them to "do a head job" - I wanted them to find out what was wrong with the engine and let me know.

When I know more I will pass it on. OD