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[paul8594]

I have read a lot of old posts and guides and still cannot find the leak in my cooling system.

The coolant light came on and i refilled whilst running the engine with the expansion cap off and heater on full. Let the fans come on and refilled to the level.

I have now done this on a number of times whilst trying to find the source of the leak.

I put the car up on ramps and found a rustry water trail on the rear of the engine bay bulkhead going up to the top of the engine.

Looking at the top i could not see where it was coming from when the car was not running and cold so went through the refilling routine and sent my hand into the back to try to find a leak. I felt a small amount of water coming from the HBV and noticed the heater was blowing cold despite being on HI.

In the meantime the water was bubbling away in the expansion tank and then overflowed like some sort of geyser, still with no heat coming out of the vents.

Refilled the water put the cap on and it all dissapeared into the system, put more water in capped it and thought good all sorted as i had checked the HBV and no leaks.

As i was getting near to time to be somewhre quickly shut the bonnet and drove off and as i did hot roasting air came through the vents!

However my joy was short lived as after a couple of short journeys the coolant light was back on and i am backto square one

I have put limescale cleaner through the whole system and i intend to back flush the heater matrix, should i replace the HBV at the same time and any other suggestions

Regards

Paul   

[amba]

Sounds like the HBV is your problem although you may also have either a restriction in the heater matrix or a partial blockage in the system.

My advise would be to purchase a new Genuine GM HBV and 5ltrs of red coolant from your local VX Stealer.

Drop the existing coolant from the sytem via the radiator drain plug..bottom corner of rad n/side.

First remove both quick fix heater hoses from the o/side bulk head and get a garden hose and runwater through both top and bottom outlet until it is running clear and steady.Next replace the existing HBV with the new unit and thoroughly check all hose clips and joints are secure.Refill entire system with the 5ltrs of new coolant and then top up with water .Start car with header tank cap removed,heater on HI setting and blower fans on fast, and leave on fast idle until temp reaches mid point carefully checking top hose for "sudden hot rush" indicating thermostat has opened.

Check coolant level and top up as required then replace header tank cap and take car for a 10 mile drive keeping eye on temp gauge.On return again check coolant level.Probably worth then leaving to cool down and recheck level.

With any luck that will have solved the problem     

[feeutfo]

You have a leaking hbv (by the sound of it) a slight leak is often made worse by setting cc to lo. Just had exactly that with mine as it happens.

The rest is a slight complication of running he engine with tha cap off. It WILL boil over in these circumstances.

Fit hbv then service the coolent if it's due. Top up if needed in a day or do as the level settles.

[paul8594]

Thanks for your replies, the problem is worse when heating is on low. Glad it is, possibly, only the HBV did'nt fancy trying to find core plug leak or anything else!

[feeutfo]

Thanks for your replies, the problem is worse when heating is on low. Glad it is, possibly, only the HBV did'nt fancy trying to find core plug leak or anything else!

There are numerous possible causes of water leak on the omega, with core plug possibly being the worst. But if yours is leaking worse on lo then that's almost certainly hbv. With scuttle off you should be able to see it leaking with engine running to confirm. But you'll have to clime in and pull the hbv off its post at the very back of the engine to see it.
It's a simple job in theory. But practice is awkward.

I'd say doable for most people, but with a lot of swearing. £40 incl vat from dealer.