Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Does this sound like a thermostat problem?
If it is the head gasket, it sounds like its only a very small leak. Tightening the head bolts may close it.
However, your problems may not be over, as leaking head gaskets can be caused by other underlying problems, rather than just a head gasket deciding its time to blow.
The usual cause is overheating. This causes extra sresses and strains and in extreme cases can cause the head itself to warp. Remember that the temperature gauge only measures the temperature of the water near it, not the temperature of anywhere else, so its perfectly possible for the gauge to be reading slightly warm even if the water around the cylinders is boiling hot. A slightly leaking head gasket can blow all the water away from the water jacket around the cylinders and replace it with air (a big airlock) so this area now has no cooling at all and so can get very hot, but at the same time there is water around the temperature sender just indicating that the temperature is rising above normal! Get a big enough airlock and it stops the pump from pumping as well.
So what can cause the gasket to blow in the first place? The car has overheated at some point due to eg a leaking pipe, a fan failure etc and the causing problem has been fixed but not the headgasket. The car will still show signs of overheating (but not as bad as before) so the owners decide its a serious problem and time to move it on while it still appears to be ok.
Well, thats one cynical view anyway.
It could well be that its simply the thermostat that is misbehaving, but I've been in the same position of hoping that it was the thermostat when all along it was the head gasket. Mine was caused initially by a blocked radiator. I replaced the head gasket twice before I found this out. Note sticking a hose in one end of the radiator and watching for water coming out the other end does not guarantee that the rad is not blocked (I did this!). Get it flow tested if you think this may have something to do with it!
Can't think of another way that air can get into the system.
I have heard that most garages can test the rad water for dissolved combustion products which is a sure way of telling if the head gasket is leaking into the water.I've never tried this so it may be a vicious rumour, but may be this should be your first approach if you are getting regular air locks.
A long post but I hope it was worth it!
Nick
