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[jayten10]

hi to all,

i have just picked up a 2.6 mv6 auto which i am afraid the previous owner wasnt very honest, the car is losing water am l to belive its the hbv? or a top hose or as the previous owner said he had trouble with the header tank cap, could it be its leaking? i am not that convinced, any help is appreciated :-/

cheers jay

[MutantCav]

Could be any of the ones you mention...although if you cant see water leaking HBV would be option 1...the water tends to leak onto the exhaust and evaporate Header tank caps do sometimes become faulty though and can cause a pressure build up as its designed to relieve pressure build up
Where are you based?? Someone on here local to you may well be able to check your car out in person

[tango]

have you topped the water up and started the car to see if you can spot the leak anywhere

[PhilRich]

Check the expansion bottle around the cap carefully for tiny cracks, the plastic is prone to failure at that point 

[MutantCav]

New expansion tank is only £25 plus VAT from Vauxhall though if thats your problem

[John_Clayton]

I've just found that my expansion tank is leaking at the base of the filler neck.

What's HBV stand for?

[amba]

HBV......heater by pass valve.

Sits at the back of the heads under the windscreen scuttle panel and looks like the starship enterprise.

It works by an air vacuum pulling up the internal diaphram and diverting hot water either through or past the heater matrix.
 
It does have a tendancy to leak but as water going through it is hot this produces steam which then evaporates so might not be totally eveident unless you can see coolant stains around it.Can also cause other issues in the long run so have a good check and if its failed replace it,but only with a genuine VX unit as pattern parts are poor quality and will fail again.

[mathewst]

One other thing. Check the hoses around thermostat if it was changed or touched recently.
My mig was loosing water only when it was running (and it was loosing more water if the aircon was on).
One hose was leaking only when the system was presurized and the engine hot enough.
Easiest way to check is to get the engine to temp and abserve