Water Pump

[Tarmac_Terrorist]

I've read that it is recommended to replace the water pump when replacing the cambelt & tensioner as it's a relatively cheap part and if it fails at a later date, the labour has to be pretty much replicated. My cam belt will need replacing in May but as the car has only done 7,000 miles, I don't really see the point in replacing the pump.

However, I understand that VW water pumps are known to fail. Can anyone tell me in what way they fail. I mean, in my limited experience, it's usually the bearings that fail on pumps and you can usually hear this develop gradually and then perhaps a slight leak. Is this the case with VW's or do they tend to fail in some other spectacular way causing the belt to snap / lose tension?

I have no major issue in spending an extra £70 for a pump whilst having the belt and bits replaced, but at 7,000 miles I can't really see what i'd be gaining? I only cover about 1500 miles per year.

[RobH]

Are you still in warrenty and hows your cambelt tensioner as you could possibly get the lot done under warrenty, loads have on here and mines in their now for the same reason, annoying churping noise.

[Tarmac_Terrorist]

I'm well out of warranty but no chirping / tensioner issues on my car. My father in law's ed30 had  his belt / pulleys / tensioner replaced under warranty last week due to the 'under bonnet budgie'!

[Gene Hunt]

7 tho is not a lot so maybe leave the pump. I know some VW garages are leaving the pump between cam belt changes if the miles are low.

[SteveTDCi]

get it done, ok its not a VW but when we had the belts changed on our puma we didn't think about doing the water pump, and now its just started to leak, ok the car is 10 years old in june and has covered a lowish 38k but i would always pay the extra knowing it should be good for a number of years. What is the cambelt change period on the 2.0T anyway ?

[nc35]

Think there is some confusion over the Cam belt change.

Most say Every 5 years or 70K but the manual says 120K

Coming up to 5yrs so will be getting it done at next service.

Prices seem to vary wildly - someone had a deal at £250 which can't be bad.  Just don't know who or where.

Bradford VW - our closest even though we live in Leeds will match or beat any genuine quote from a dealer or independent... 

[ub7rm]

Two weeks ago I had a reminder from my stealer that the cam belt was needing done as it was 4 years old 

Quoted price was £520 not including the water pump.

Yesterday I got a voucher from them valid till August to get the belt changed for £299    Pump will be extra.

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

[RedRobin]

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

....That's what I was independently told and later confirmed by my friendly VW dealer.

[TagnuT]

Two weeks ago I had a reminder from my stealer that the cam belt was needing done as it was 4 years old 

Quoted price was £520 not including the water pump.

Yesterday I got a voucher from them valid till August to get the belt changed for £299    Pump will be extra.

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

I got told this this week  4 years or 60k....

[QD MBE]

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

....That's what I was independently told and later confirmed by my friendly VW dealer.

Not sure about that.

I think the prime culprit is the hot and cold incessant cycle the plastic has to endure, which makes the plastic age harden and  brittle.  The Bearings would take the brunt of the De tensioning/Tensioning.

The impeller is on the shaft and unless the shaft has the capability to force the impeller to be stressed against the orifice it sits in, the the only forces the impeller is subject to is the rotational shear force the coolant can induce, and the afore mentioned H/C cycling.

[QD MBE]

The De-tensioning and tensioning will produce leaks about the shaft seals, but not shear the impeller off.

[ub7rm]

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

....That's what I was independently told and later confirmed by my friendly VW dealer.

Not sure about that.

I think the prime culprit is the hot and cold incessant cycle the plastic has to endure, which makes the plastic age harden and  brittle.  The Bearings would take the brunt of the De tensioning/Tensioning.

The impeller is on the shaft and unless the shaft has the capability to force the impeller to be stressed against the orifice it sits in, the the only forces the impeller is subject to is the rotational shear force the coolant can induce, and the afore mentioned H/C cycling.

Regarding the H/C cycle; there is some truth in what you say there, it contributes to the failure but is greatly accelerated by the new belt.  This isn't unique to VAG, its a common problem with most water pumps / engines.  The most common time for pump failure is shortly after the belt is changed. 

To be pedantic its the impeller that induces a force on the fluid, the fluid merely provides resistance.   

I suspect that the tensioing / retensioning causes the shaft and impeller to move slightly off centre which adversely changes the flow around the impeller, concentrating stresses where they are not designed to be and ultimately resulting in failure. 

[RedRobin]

^^^^
Ah, thanks for the correction, stokey  

Either way, it's definitely advisable to change the water pump when changing the cambelt.

[Garth]

Oh dear, I've done 66k (05 plate) and not had either cam belt or water pump replaced yet.

I just had a service last month and he dealer marked my water pump as 'orange' on the check list indicating that it is worn. They never mentioned the cam belt though.
I thought they were good for 80k?

[QD MBE]

I believe the failure mode is that the impellers shear off the spindle, and there is a theory going about that the stress of detensioning and retensioning with a new belt is actually the prime culprit in causing this.  Thats why you should get a new pump with a new belt.

....That's what I was independently told and later confirmed by my friendly VW dealer.

Not sure about that.

I think the prime culprit is the hot and cold incessant cycle the plastic has to endure, which makes the plastic age harden and  brittle.  The Bearings would take the brunt of the De tensioning/Tensioning.

The impeller is on the shaft and unless the shaft has the capability to force the impeller to be stressed against the orifice it sits in, the the only forces the impeller is subject to is the rotational shear force the coolant can induce, and the afore mentioned H/C cycling.

Regarding the H/C cycle; there is some truth in what you say there, it contributes to the failure but is greatly accelerated by the new belt.  This isn't unique to VAG, its a common problem with most water pumps / engines.  The most common time for pump failure is shortly after the belt is changed. 

To be pedantic its the impeller that induces a force on the fluid, the fluid merely provides resistance.   

I suspect that the tensioing / retensioning causes the shaft and impeller to move slightly off centre which adversely changes the flow around the impeller, concentrating stresses where they are not designed to be and ultimately resulting in failure. 

So the impeller is rotating as you as fit the belt?  It doesn't matter where the impeller sits within the void within the engine block, unless it touches the block, nothing will affect it.  Unless the seal is gapped, then you will get a leak, the pump will still be rotating.  The impeller will still be doing its job.

I have changed 2 VW water pumps recently, and both broke up and crumbled in my hands, the plastic has become very brittle due to H/C cycles, nothing to do with differing flows around it.

you are right, the fluid will induce a resistance to rotation, this is a shear force trying to twist the impeller off,  but I think we are talking about the same thing.  Tomatoes and red things!

in the pic below you can see the cracks and how aged, brittle and crumbly the plastic has become.