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[Varche]

About a week ago, I changed the coolant and did a comprehensive back flush to remove brown looking water. Refilled with VX correct antifreeze and water mix. Got it up to temp, heater on, off, air con on cold etc. Topped up, went tfor a drive. OK Next day took trailer and hauled a ton of sand back, heater on lovely and warm. Temp fine, in fact a Spanish passenger remarked it was high at 94. No quoth I. Normal

Today went on a hundred mile trip and at the distant end (half way) was dismayed to come back and find that there was coolant dripping out from behind the engine somewhere. Couldn't see where as it had stopped. Topped it up about two pints lost and I had checked the level before setting off.

Set off for home with lots of trepidation. Didn't use the heater got home with temp still on 94 (or mid point what ever that is). No dripping water, tried it through all scenarios. Heater flat out, air con on ice cold, no heater. Couldn't get any water loss. It has cooled now and guess what the level is exactly what it was 50 miles ago!!! No stains around the water header tank cap.

Haven't got any hair or nails left anymore. Any suggestions? 
More self healing from the worlds only self healing Omega!

[dbug]

Maybe all the airs out now?

[geoffr70]

Well i don't want to state the obvious, but HBV? Mine behaved very erratically when it went defective :-?

[Andy B]

Well i don't want to state the obvious, but HBV? Mine behaved very erratically when it went defective :-?

Same as mine when it last failed. It was OK with the a/c off, but leaked with the a/c on. It took an hour to change. 

[Debs.]

Same symptoms as when my HBV failed.

[fiend61]

{ditto} same as my hbv ( very thin arms needed) or as i had a very long pair of longnose pliers 

[Varche]

Already had two of those in the last five years. Both were VX not pattern. I have saved one that I replaced "just in case" Might try on that and have a look at the one that is on. How can you tell they have failed? Where do they actually leak from?

[Andy B]

..... How can you tell they have failed? ....

They leak coolant 

Where do they actually leak from?

There's a diaphragm in side it that the vacuum acts on to move the valve. The diaphragm had perished on mine which was where the leak was from.

[Varche]

Anywhere online that sells genuine VX parts before I resort to someone in the UK or andyc? I suspect that most of the parts  on EBay.uk are pattern and to be avoided....

[Richard A]

Changed my HBV three times in 3 years (80k), each time with a GM unit.
They leak because they just wear out.
The HBV is working all the time the engine is running, as the valve continually mixes the coolant to achieve the temp set on the heater control, it's the seal that leaks.
regards
richard a

[Abiton]

Changed my HBV three times in 3 years (80k), each time with a GM unit.
They leak because they just wear out.
The HBV is working all the time the engine is running, as the valve continually mixes the coolant to achieve the temp set on the heater control, it's the seal that leaks.
regards
richard a

Mixes it with what?

[Richard A]

Very hot coolant and cooler coolant is mixed so the temperature in the car stays constant, at what ever temp you have set, just like a 'mixer tap' or 'shower temp mixer'.
The HBV is adjusted by the 'vacuum' attached at the top of the unit.
regards
richard a   

[Entwood]

HBV does NOT "mix" coolant in any way shape or form ... It is called a "Heater Bypass Valve" because thats what it does ....

When heat is required the valve moves (under vacuum control - actually "no vac" gives heat) to direct the flow through the heatr matrix.

When heat is NOT required the valve moves (under vacum) to shut off the flow and BYPASS the matrix.

The vacuum is controlled by a solenoid (behind the glove box on facelifts) and is either there or not .. no modulating at all.

The HBV has moving parts, is made from rubber, and is subject to varying temperatures from very hot to cold... therefore the rubber has a tendency to split and leak. Depending which side splits it can leak either when not bypassing (hot) or when bypassing (cold) .... either way it needs replacing if leaking ...



HTH

[feeutfo]

Have a look around the back of the engine for signs of coolant residue same colour as your coolant. Follow the clues. But ultimately applying pressure to the coolant bottle can show the leak, although settings can affect when the hbv leaks as said.

[Malcolm_D]

..... How can you tell they have failed? ....

They leak coolant 

Where do they actually leak from?

There's a diaphragm in side it that the vacuum acts on to move the valve. The diaphragm had perished on mine which was where the leak was from.

Sorry if I am being a bit dim but while I can understand the diaphragm perishing, leaking and stopping the hbv from performing as it should surely it is contained within the sealed casing and the only place the coolant can go is elsewhere within the system i.e. down one of the 3 hoses connecetd to the hbv? How is the coolant able to leak out if it is not the casing that is also at fault?  :-?