Whilst I know it would be good practice to drain entire cooling system to change the expansion tank, can I get away with just draining the expansion tank and refilling the new one? Am I likely to have a problem with airlocks if I do?
Thanks in advance for assistance...
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I think you should be fine. I've replaced things on the A4 tdi (afn) without problems. Just let it run for a good while and top up as needed.
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I have to ask why !!. Has it cracked or what. If the fluid if clear and the right colour then syphon the contents of the tank out and retain. Keep the pipes up and remove the tank, fit the new one and secure it then refill the tank. Run the engine with the cap off, top up if necessary and replace the cap. Check the leval again after a run. Regards Peter
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Thanks both for responses. Reason, Peter, is that I have been losing collant on an accelarating level. Car now has 180k + miles: audi specialist who serviced it last says that tank may have distorted (does seem to be some coolant around the seam) so as a first attempt, am replacing tank and cap.
Tim
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My Passat 1.9 PD was losing coolant at a steady rate and it proved to be a corroded radiator. Was impossible to see without dismantling. Not cheap to replace but at least it was not HGF.
Good luck.
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Rads are a common problem on the A4 tdi - the mounting includes a splending spongy thing that seems designed to allow corrosion. Thats a bumper/front of car off to fix (possibly do timing belt as well while its all exposed depending on miles etc)
But cracked expansion tanks are also quite common. They seem to reach a point where the plastic ages and gets brittle.
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But on my VW the cracked expansion tank was caused by over pressuring due to cracked head, at 180K , it must have some cracks, although very small ones. Have you checked that out?
If it is 'old plastic' causing the problem then you are lucky, and can change it very quickly without any hassle of draining system
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Will report back with progress. Will do the job tomorrow if its above freezing, and not raining. (Wimp)
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If thew weather is rubbish just change the cap and try it. However excessive, but steady over pressurisation of the header tank can cause the pressure vent 12 to 14 psi from memory to seep coolant form the cap and it collects at the seam. This can be cuased by a perished 'O' ring in the cap so wrap a length of either steel blue of kitchen paper around the cay and hold it on with an elastic band. Run for a day and inspec the tissue for signs of any leakage. Regards Peter
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Weather is rubbish (-3.5 at 10:30!) have already changed the cap. Peter, with no joy.(continued coolant loss) Maybe it will warm up this afternoon....
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But have you done the paper around the cap to rule out the cap leaking?
Are the rubber pipes getting very hard? ie overpressure?
Any drips from the rad?
When its this cold it might be easier to spot small leaks by steam
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OK: job done. Seems to have resolved water loss, and level is now maintained in the expansion tank. Had a reasonable run on Monday (120 miles including Mway) and coolant now seems fine. I do however, have an induction roar, which seems to coincide with the turbo "kicking in" and comes from the passenger side of the engine. Anyone have any ideas? When it was serviced (pre xmas) mechanic said he could see no sign of leaks or similar that might be causing it...
Tim
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If its the same layout as my Passat, check the rubber air pipe that connects from the intercooler under the nearside headlight to the plastic moulded air pipe that runs around the back of the engine.
Inspect it carefully looking for a very small split.
I only found the split on mine after I noticed a fine spray of oil on an adjacent water pipe that had blown from the split.
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Yup, dieselnut, spot on. Correct pipe, split at first elbow where it bends down from plastic pipe. Temporarily gaffer taped, which has reduced induction noise to barely audible whistle, so will order new pipe tomorrow. However: seems to have returned the expression of coolant problem. Could the two things be connected? Peter: you mentioned over pressure due to cracked head: would I get any other symptoms of this?Certainly the coolant seems to be leaking at the join of the cap, and it is both new tank and new cap. Do I need a mechanic to check what pressure coolant system is running at?
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coolant seems to be leaking at the join of the cap, and it is both new tank and new cap. Do I need a mechanic to check what pressure coolant system is running at?
It's running at, or very slightly above, the blow-off pressure rating of the cap.
Edited by Dave_TD {P} on 18/01/2009 at 23:05
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Glad that my input was helpfull.
' However: seems to have returned the expression of coolant problem. Could the two things be connected? '
Now that you have the full turbo pressure going to the cylinders the engine will be under more stress. So any weakness such as head gasket or slight crack in the head will be more likely to leak if just marginal.
Get the coolant sniffed by a local garage for hydrocarbons which should show any problems.
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Get the garage to use their kit to sample the gases from the header tank, these may be combustion gases and indicate a larger problem, a head gasket failure. Regards Peter
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