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[bob.dent]

Sorry, don't usually post non-Omega problems on here but if anyone could shed some light on this it would be much appreciated. My best mate is at his wits end with his W reg BMW 735i. He is having horrendous problems with too much pressure in the cooling system and so far is on his third header tank due to them splitting under too much pressure in the system. He was initially told that is was likely HG failure but this has proved non conclusive following all manner of tests for HG failure. Another diagnosis was that there was air in the system but having been bled several times the problem is still there - the pressure actually blew one of the main hoses clean off a couple of days ago. He now faces an expensive dilemma of letting the garage strip the engine down to check for HG failure when it may not be necessary.
Any help or advice would be much appreciated as he really doesn't know what to do next.

[Jimbob]

[movedhere] Omega General Help [move by] Jimbob.

[Jimbob]

Sorry Bob, gen car chat for this one 

[bob.dent]

Sorry Bob, gen car chat for this one 

No problem James, I did wonder.

[djac]

IIRC there was a thread on here recently about a mig tractor that was over-pressuring? One possible cause that was mentioned was the water pump - -I think.

[serek]

check water pump first and pressure on cyl.

[bob.dent]

He recently had a new water pump fitted along with a new thermostat. Unless it's faulty or the wrong type I think that can be ruled out but worth checking.

[Kevin Wood]

First question, IMHO, is why the pressure cap on the header tank is not relieving the pressure?

I take it the cap was replaced when the tank split though?

If the system is pressurising excessively without the engine actually overheating it does sound like head gasket to me.

Might be worth a pressure test and a careful check for leaks, though, in case a leak is drawing air into the system as the engine cools, which later forms an airlock.

Does it start OK? Any misfire immediately after startup?

Kevin

[bob.dent]

First question, IMHO, is why the pressure cap on the header tank is not relieving the pressure?

I take it the cap was replaced when the tank split though?

If the system is pressurising excessively without the engine actually overheating it does sound like head gasket to me.

Might be worth a pressure test and a careful check for leaks, though, in case a leak is drawing air into the system as the engine cools, which later forms an airlock.

Does it start OK? Any misfire immediately after startup?

Kevin

Thanks Kev, not sure if he had the cap replaced, I'll find out. He has had pressure tests done but as said, nothing conclusive to show HG failure. Car starts and runs absolutley fine.

[mantahatch]

I suppose it is possible that the new thermostat is faulty, but to be able to build up enough pressure to blow a pipe off, I would check very carefully the circulation of the coolant, I mean is the rad getting warm all the way across it.
Failing all that in previous posts I would have to go for headgasket.

Has the engine been frozen at all ? in the cold weather.

[Kevin Wood]

What does the coolant look like? Any sludgy brown substances in the header tank? Any staining of the plastic?

Kevin

[bob.dent]

I suppose it is possible that the new thermostat is faulty, but to be able to build up enough pressure to blow a pipe off, I would check very carefully the circulation of the coolant, I mean is the rad getting warm all the way across it.
Failing all that in previous posts I would have to go for headgasket.

Has the engine been frozen at all ? in the cold weather.

According to his mechanic the coolant circulation is fine and no problem with the radiator. Engine has never been frozen - has good antifreeze and serviced regularly.

[bob.dent]

What does the coolant look like? Any sludgy brown substances in the header tank? Any staining of the plastic?

Kevin

I don't know what the original header tank was like as he's now on the third new one, but I'll see if I can find out what the condition of the original was like.

[mantahatch]

Many years ago had a mark 1 Cavalier. It would idle all day with no problems and even if you revved it whilst statinary there where no problems.
But drive it little over 1 mile and it would blow the rad cap off, which I did not think was possible.

Turned out to be cracked head. later discovered that it was not uncommon on the Cavalier CIH engine, but there was no overheating or problems prior to it happening.