when you had the thermostat out did you feel the pump to see if it was fooked ?? my money still on water pump.
A failed water pump wouldn't pump coolant and a stream of bubbles round the system. The bubbles have to be coming from somewhere in the system, and I can't put my finger on anywhere else that it could be occurring.Is there coolant circulating through the header bottle? If so then the water pump is working. This small stream of bubbles leads me to think that the head gasket is passing combustion gas (very high pressure) into the coolant waterways (relatively low pressure) and that's what is pressurising the coolant.
Mine did...the impeller had just enough grip on the shaft to turn - it was slipping but still turned. Enough to pump water round at idle and keep the temps under control under light load. Constant load for a few minutes though, and it couldn't cope - resulting in boiling coolant pissing out of the header tank.A failed water pump wouldn't pump coolant and a stream of bubbles round the system.
Mine did...the impeller had just enough grip on the shaft to turn - it was slipping but still turned. Enough to pump water round at idle and keep the temps under control under light load. Constant load for a few minutes though, and it couldn't cope - resulting in boiling coolant pissing out of the header tank.
In other cases, I understand bits of the impeller break off, which would lead to a similarly reduced cooling capability.
Personally, if my car had already covered 47k on the current cambelt, I'd get the belt & pump done now, and see if that cures it.
Only one way to be sure really and that's take the bull by the horns.
Tell you what, I'll make a bet that I'm right about the head gasket and I'll be happy to lose it. You take a bet on the water pump and I hope you're correct. That would be the cheapest option.![]()