coolant, again

[colnet]

Right, ive got a 2000 B4204t2 v40 auto, 124k, on long runs absolutely no coolant loss, on pottering about she will go from max to min on the expansion tank within about 10 miles.
No puddles, coolant pressure test was perfect, UV dye in, can see no leeks, runs like a dream with no smoke or steam, scratching head the only thing I can think of is waterpump? Coolant maybe burning off instantly so cannot be seen leeking, but wouldnt she do this on long runs? She had a new cam belt and bits at 90k.
I know all you knowledgeable people will know the answer so a big thankyou to you all.

regards

[loely]

If the waterpump leaks you shouls see a trace where the water runs befor drying on the heated motor.Does the fan kick in?While driving on the long runs there is a lot more cool air passing trough the radiator and preventing from warming up.
When driving at slow speed the air will not cool down the radiator enough.Certainly when ideling for longer period.

[colnet]

Hi loely, cannot see any trace of water leakage anywhere, even near the waterpump, the fan kicks in as it should, never on long runs, the temp gauge also stays exactly where it should be long or short runs but I do check the level each morning which is how I found out it only losses coolant on short runs.

[Phandy]

I had a similar problem on my 2003 V40 Auto. I was losing coolant and could not work out how or why. i went through it all from water pump to possible head gasket.

Replacing the expansion tank cap was the solution in my case. I purchased a 2nd hand expansion tank and cap off ebay and quickly fitted the cap with a view to fitting the tank at a later date, but the new cap did the trick.

As I understand it, as the coolant system got under pressure, the coolant rose in the expansion tank as it should, but was seeping out via the cap which was not creating a full seal. Incidentally, the cap looked fine.

I would by a 2nd hand one like this for 10 GBP, it is worth a shot

http://www.ebay.co.uk/itm/VOLVO-V40-...0AAOSwnK9ZSkTH

[colnet]

Cheers phandy, have tried a new cap and also a cap off another v40 which I know was working fine and still had exactly the same problem, I just have a gut feeling it is something to do with the waterpump, or, maybe the expansion tank itself but then again surely I would see signs of a leak, last week drove 200m in one hit, no loss of coolant, yesterday 10m pottering about it went from max to below min, go figure.

[960kg]

The expansion tanks do have a problem of hairline cracks which are at the back so you cannot see them properly.

Also always use the Volvo cap and not the aftermarket ones as they can be faulty. Volvo used to be green and the aftermarket black?

[colnet]

Cheers 960kg, have tried genuine volvo, pattern and an old genuine off my old v40 which i know was working fine but still had exactly the same problem, have thought about the tank itself but i do have uv dye in the coolant so would of thought a leak would show especially as nothing gets really hot in that area, once again thanks for your help.

[V40T4R]

Hi, do you need to top up coolant?

[Richardkimber]

My V40 1.8 petrol no turbo does exactly the same. Have had the car for three years. If I top it up to max when cold it blows out of the expansion tank when hot. I never lose any coolant if the level is at min when cold. No overheating or loss of coolant. It's definitely holding pressure as when the cap is released when hot it does release pressure.
Unusual behaviour.

[colnet]

Hello Richard, yes mine is holding pressure as well, when I check when cold I always top up to the max Mark, I will now try and leave it at the min Mark and see what happens, checking constantly I might add, cheers.