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[NaughtyNigel]

I have suffered slow coolant leak from my 2.5 V6 (facelift) for two or three years now, but have never found the source. I can nearly always smell hot antifreeze after a journey but until Saturday I have never seen anything.

Coolant consumption seems highest after short (10 ~ 15 mile) journeys, whilst 200 mile journeys use very little at all. Until a week or so ago it was using about one litre of antifreeze per 500 miles on mainly short journeys.

Anyhow, it has been getting much worse recently, and on Saturday, when I changed the front brake disks, I could see telltale pink streaks on both sides of the bell housing aft of the engine. There were also two small pools of antifreeze on the drive.

From what I have read here, this all points to the Heater Bypass Valve (HBV). However, peering behind the right hand side of the engine with a torch and mirror the HBV was perfectly clean, and there was no sign of coolant leakage anywhere around it.

Looking from the left hand side I could just see the top of the ignition coils (DIS Packs?), which were also clean.

So my question is; how, where and why does the HBV leak? And does this sound like a typical HBV leak? If not, where is the coolant most likely to be coming from?

The car has done just over 100,000 miles, the engine oil is perfectly clean and there is no 'mayo' around the filler neck, so I don’t think it is the head gasket or the oil cooler. In all other respects the car starts and runs perfectly.

Any advice would be very welcome as I would like to be able to use the car without worrying about loosing coolant all the time! 

NN

[Marks DTM Calib]

Thats does not sound like a typical HBV leak, its to little for to long.

Yours sounds more like oil cooler plate seal or thermostat seal in the valley area.

[NaughtyNigel]

Thats does not sound like a typical HBV leak, its to little for to long.

Yours sounds more like oil cooler plate seal or thermostat seal in the valley area.

That seems to make sense.

Are these easy enough to change?

NN

[serek]

this will help http://www.omegaowners.com/forum/YaBB.pl?num=1221081908
and for thermostat http://www.omegaowners.com/forum/YaBB.pl?num=1229464812
 

[NaughtyNigel]

Ahaa. Thanks for that. Looks like my weekend is planned then.   

NN

[NaughtyNigel]

Thats does not sound like a typical HBV leak, its to little for to long.

Yours sounds more like oil cooler plate seal or thermostat seal in the valley area.

For future reference, what actually happens when the HBV fails? Does it break open or split, or is it less obvious than that?

NN

[GastronomicKleptomaniac]

Thats does not sound like a typical HBV leak, its to little for to long.

Yours sounds more like oil cooler plate seal or thermostat seal in the valley area.

For future reference, what actually happens when the HBV fails? Does it break open or split, or is it less obvious than that?

NN

 Mine sent a dribble down the rear of the engine.

[markfree]

I had much the same symptoms as you and I felt behind the HBV and couldn't feel any coolant so decided to strip the inlets off down to the V - pressuried the system and lo and behold it was ....................HBV so I'd seriously check this one out first altho' taking the inlets out made it an easier job.
My HBV looks perfect from the outside - it's the innards that fail.

[GastronomicKleptomaniac]

There's a very well-written HBV how-to guide, in the maintenance section. *ahem*

[NaughtyNigel]

There's a very well-written HBV how-to guide, in the maintenance section. *ahem*

I have just found that. Thank you. 

NN

[dbug]

Thats does not sound like a typical HBV leak, its to little for to long.

Yours sounds more like oil cooler plate seal or thermostat seal in the valley area.

Or coolant bridge.

[feeutfo]

have a look here, http://www.omegaowners.com/forum/YaBB.pl?num=1244468227/15
Covers alternative leak areas other than hbv and tips how to diagnose. Unfortunately most leaks end up dribbling down the back of the engine on the bell housing area.

[NaughtyNigel]

Its strange. I used the car a few times on Sunday, two short (3 mile runs), and two 15 mile runs later in the day. Then my wife took it to work yesterday (11 miles each way). Last night the Coolant Low warning came on, and had to add more than a litre to bring it up to level.

My wife took it to work again today. It lost virtually no coolant today, but it started dribbling an hour or so after she came home. :question

Think I'll see what happens when the heater is turned up full. People here seem to say that turning up the heater can make the HBV leak. :question

[feeutfo]

Its strange. I used the car a few times on Sunday, two short (3 mile runs), and two 15 mile runs later in the day. Then my wife took it to work yesterday (11 miles each way). Last night the Coolant Low warning came on, and had to add more than a litre to bring it up to level.

My wife took it to work again today. It lost virtually no coolant today, but it started dribbling an hour or so after she came home. :question

Think I'll see what happens when the heater is turned up full. People here seem to say that turning up the heater can make the HBV leak. :question

Hbv is actuated by vacume and depends on the climate controle settings as to its position and where its rooting the coolent. It then depends on the exact leak site on the hbv as to what climate setting gives the leak. I presume when the engine is off and the vac is lost the hbv position changes and then it leaks out more dramatically.....Sometimes. Sometimes they leak no matter what.
 As said, depends where and how bad the leak is and what the climate settings are. Iirc Mat(in the link) said his leaked steadily for weeks and then it got worse and poored out when engine off. Certainly when we topped it back up and started the engine no leak could be found. When i checked the climate setting it was on"lo", flat out ac. When set to "hi" flat out heat it poored out. No reason to assume yours will behave exactly the same though.
But should give you something to work on. :-)

[NaughtyNigel]

Thanks for that Chris.

I took it to our local independent garage this morning for them to have a look at.

Problem is, about a year ago they diagnosed a failing head gasket, on the grounds that they found Carbon Monoxde gas in the header tank, and they seem reluctant to consider anything else. But what other gas would you find in a coolant header tank anyway?

The coolant had been circulating in the system for around 5 years/50,000 miles, and even a 'perfect' head gasket will be slightly permeable to a small molecule like CO over a long period.

Has anyone here tried using an exhaust gas analyser on a good/newish engine? 

Right now I feel as if I am banging my head on a brick wall. I don't mind paying a reasonable amount to get it put right, but I don't want to spend good money on an expensive fix that cannot work.

NN