Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[101 Tommy]

Hi all, got an overheating problem with the Omega...

The coolant system is over-pressurising after about 5 minutes running from cold, the water stops circulating and boils out of the reservoir. I have no loss of coolant, no smell of combustion gas in the coolant, and seemingly perfect running on all cylinders.

My first thought was that the head gasket has a tiny leak between a combustion chamber and water jacket. Although i've heard that the heater bypass valve can allow air into the coolant and cause over-pressurising of the system, but looking at the new part I got today I can't understand how it would let air in but not out. Has anyone had this problem before and found that changing the HBV cured it?

Tom 

[Lazydocker]

Sure the thermostat is opening?

[NiallyV6CDX]

Are the radiator top and bottom hoses getting hot? If not its likely the thermostat has seized shut.

[101 Tommy]

Thanks guys.

I changed the thermostat already, and put a new cambelt on while I was there as I went in from the front of the engine. I checked in hot water if the thermostat opened correctly, it did look a little suspect so thats what made me think it might be that before. The new one I installed opened up much more readily in the hot water. The radiator pipes get hot as they should, and I also flushed the radiator out when it was off. It didnt appear to be blocked and both compressed air and water from the hose went through it nicely.

A further development today is that I took off the scuttle and the wiper motor out and I cant see a heater bypass valve there at all! I even just took the plenum off to make sure and its just not there. Its not that small a part so I think it would be quite difficult to miss something like that. The heater matrix coolant pipes attach to a casting on the engine, and they are the only two pipes there which look like they are the right size to attach to the HBV.

This has completely thrown me now, looks like the only option I have left is to change the head gaskets. Does anyone know of certain of these V6 engines not having a HBV? Surely it is necessary to switch the heater from hot to cold? I know the MV6 i've got has minimal equipment, but it still has a heater!

 :-/

[dbug]

Yup should have an HBV mate 

[Jimbob]

should have one, but we have heard of them being removed in the past.

can you post a photo of the general area, or is it back together now?

[101 Tommy]

I thought so. No its not back together yet, i'm kind of preparing myself do do the heads.

I'll go and get a camera and get you guys a pic. The DIS pack and the regulator on the end of the fuel rail are clearly visible, and from pics of other people's cars it should be right there. It just doesn't look like it is.

[Abiton]

Thanks guys.

I changed the thermostat already, and put a new cambelt on while I was there as I went in from the front of the engine. I checked in hot water if the thermostat opened correctly, it did look a little suspect so thats what made me think it might be that before. The new one I installed opened up much more readily in the hot water. The radiator pipes get hot as they should, and I also flushed the radiator out when it was off. It didnt appear to be blocked and both compressed air and water from the hose went through it nicely.

A further development today is that I took off the scuttle and the wiper motor out and I cant see a heater bypass valve there at all! I even just took the plenum off to make sure and its just not there. Its not that small a part so I think it would be quite difficult to miss something like that. The heater matrix coolant pipes attach to a casting on the engine, and they are the only two pipes there which look like they are the right size to attach to the HBV.

This has completely thrown me now, looks like the only option I have left is to change the head gaskets. Does anyone know of certain of these V6 engines not having a HBV? Surely it is necessary to switch the heater from hot to cold? I know the MV6 i've got has minimal equipment, but it still has a heater!
 :-/

No aircon?

My understanding is that if your miggy doesn't have aircon, it won't have an HBV.  Have yet to hear of one that goes against this theory.

HTH.

Pete

[Elite Pete]

Thanks guys.

I changed the thermostat already, and put a new cambelt on while I was there as I went in from the front of the engine. I checked in hot water if the thermostat opened correctly, it did look a little suspect so thats what made me think it might be that before. The new one I installed opened up much more readily in the hot water. The radiator pipes get hot as they should, and I also flushed the radiator out when it was off. It didnt appear to be blocked and both compressed air and water from the hose went through it nicely.

A further development today is that I took off the scuttle and the wiper motor out and I cant see a heater bypass valve there at all! I even just took the plenum off to make sure and its just not there. Its not that small a part so I think it would be quite difficult to miss something like that. The heater matrix coolant pipes attach to a casting on the engine, and they are the only two pipes there which look like they are the right size to attach to the HBV.

This has completely thrown me now, looks like the only option I have left is to change the head gaskets. Does anyone know of certain of these V6 engines not having a HBV? Surely it is necessary to switch the heater from hot to cold? I know the MV6 i've got has minimal equipment, but it still has a heater!

 :-/

I think its more than likely a police special rather than an MV6. Is the car white?

[Welung666]

Has the waterpump been changed? I'll bet not! It sounds to me like the water isn't being circulated.

[Alex Wood]

That was my first instinct as well, water pump. Can you see coolant running through the return pipe back into the expansion bottle? Could probably test in a messy but effective way by turning the engine over with a water hose disconnected, you'll soon see it it's pumping!

This reminds me of an overheating problem I had with the Monza when the heater matrix was bypassed. In the end a flush with 2-stage aggressive chemical stuff sorted it out but by that time I had also found a replacement heater matrix and plumbed it in under the bonnet as a temporary measure. If something that should be in the system isn't then it might be slowing the circulation. You have a heater but not a bypass valve - I spose it's possible the heater matrix is blocked up, are you getting heat in the cabin?

What about the cooling fans, are they cutting in?

[101 Tommy]

Hi guys cheers for the replies.

I did find out as Pete said from my local Vaux dealer that if the car doesn't have air-con then it won't have a bypass valve.

I've has the water pump off already, and checked it all as I was suspicious of it too but no problems there. The water is definately circulating until the system gets full of air, and the only way it will run and not boil over is to run it with the cap off. It bubbles in there but doesn't boil. I'm pretty sure i've got a small leak from a combustion chamber to water jacket, it really cant be anything else as any other possible avenues have already been eliminated. The HBV was my last chance, but as i've discovered it doesn't have one.  :-/

Also yes the car is ex-police, but still an MV6.

I haven't got time to sort the head gaskets now because i'm off to work in Spain for a few months end of next week, so i've ended up getting a 525tds E39. Same motor as the diesel Omega I believe, the M51.

Thanks for your help chaps, much appreciated