intermittant coolant loss

[scootir706]

Hi there,i have a 03 130 tdi 4m and i have a problem with coolant loss.
Car runs perfect and temp never goes over 90[centre of gauge].
Sometimes it can go 4/5 days and other times 2/3 days before needing
about a pint or so to top up header tank.No obvious leaks and no oil/water
contamination.Last time i topped up i just used straight water with no a/f and noticed that
when i went to top up this time that the water in header tank was still clear.
I ran the car up to normal temp and took the small expansion hose at header tank off
and even revving car up to 2500/3000 there is nothing coming through.top and bottom radiator
hoses are cool.does anyone else think im right in suspecting the water pump impellor is either.slipping on the shaft or missing a vane or two?Any thoughts on this would be much appreciated.

cheers Ian

[tony-1977]

Sounds like the water pump, as you said.

If it was me, I'd change the water pump, and give the cooling system a good flush at the same time :)

If it still loses coolant with no leaks, I would then suspect the head gasket is starting to fail (between a cylinder and a waterway, hence no coolant in oil)

[scootir706]

thanks for the input....going to have a closer look at weekend.........i still suspect the water pump although there is a small
amount of water now returning to the header via the small pipe i dont think its as much as it should be when revved to about 3000 rpm.there are no tell tale head gasket signs.......no pressure build up .temp never goes above normal....no oil water contamination etc

[Toonmania]

the pump might not have completely failed but some of the impeller might have started to disintegrateas they are plastic on the genuine pumps, but with the lack of water coming out of the overflow pipe on the header tank i would say it was pump failure

[996jimbo]

It is worth also having a very good look at the bottom corners (in particular) of the radiator which commonly corrode and leak - no point in getting stuck in to the water pump if the rad is leaking.

[Thon]

I would second 996jimbo - the rad failed on 2 of my TDI 130 Passats and showed the same intermittent coolant losses. Would check rad as first port of call and from my recollection it can be tricky to see the leak. Also if it maintains a steady temperature, not sure there's any reason to suspect water pump either?

[Toonmania]

not sure there's any reason to suspect water pump either?

Errrrm lack of water flow out of the return hose on the header tank gives an exceptionally good reason to suspect a failed water pump, but it's not the reason you are loosing water as has been said that can be down too the radiator

[Thon]

Errrrm lack of water flow out of the return hose on the header tank gives an exceptionally good reason to suspect a failed water pump, but it's not the reason you are loosing water as has been said that can be down too the radiator

Really? The car maintains its temperature perfectly and you suspect the pump because of the lack of return flow? As I understand it, the expansion tank is precisely as it is named - it allows the coolant somewhere to expand into under heating and pressurization, but I wouldn't expect a massive flow through it myself as generally the inlet and outlet pipes are not huge on most of the vehicles I have had.

[996jimbo]

As Thon says - my assumption has always been that the header is not in the main circulation but is on a 'passive' loop in the system, so circulation through the header is incidental to the coolant circulation system. What I mean is there is no reason to expect to see a high flow of water through the expansion bottle. But that's my assumption and I don't actually know the answer.

Plus if was the water pump is loosing vanes you've surely got to start panicking about where those broken bits are going haven't you?

It might be the water pump, but the probability is that it's the radiator because radiators commonly leak (mine did too - bottom o/s corner).

[Toonmania]

Ok Thon & 996jimbo :notworthy:notworthy
Can't understand people putting the OP off doing the test at least :banghead: all you need to do is pop off the top hose off the coolant expansion bottle, put it in a bottle or a suitable container, and rev the engine to 1500-2000rpms, there should be a steady flow of coolant come out the pipe which will show if the waterpump is working as it should watch this video if your not sure http://www.youtube.com/watch?v=H-jxly2ZssM
radiators commonly leak but genuine VW waterpumps commonly fail too :bigeyes: and due to the lack of flow the OP needs to do this test it's pointless putting a new radiator on if it's not going to cure anything and as i have already said it could be the radiator too, but best to find out at the same time otherwise you will fill the system after fitting a new rad only to have to drain it again to refit a waterpump.
but it's up to you after all it's not my car and not my money, just trying to help you :sadwavey:but the test above is FREE should you need to test the waterpump in the future :beerchug: i'm :outtahere

[scootir706]

Ok was going to futher investigate the coolant loss this weekend but stopping to buy a lottery ticket on way home tonight seems to have given me the answer;). I had just done a 20 mile run and parked the car for about 5 mins and on returning noticed a pool of water just under the radiator hose area at the front of the car.Seems its not losing coolant when running but when parked after a good run then stopping when it cools off after a short while.car is usually parked on stone chipped driveway so hence never saw anything under the car before.ill have a closer look tomoro and let you peeps know how i get on.

[scootir706]

Well turns out radiator was shot in both bottom corners.got new one from dingbro for £54.Went the extra mile and did the timing belt and water pump while stripped.Also alt belt tensioner fell to bits when removed to do belt so heres hoping thats everything fixed in one fell swoop.:D thanks for all who gave advice.much appreciated.