Thread: V8 coolant over pressurizing

Does sound like a classic HG issue.

Ok thanks. I guess I was hoping there was some other weird reason for it happening but if it HG then he'll just have to fix it.

sounds classic HG.

Cheers

Not a crack in the header tank, or that stupid hose from the inlet manifold? Just a thing to check before big jobbing it.

Tell him to remove all the spark plugs and look for an oddly coloured one. Coolant contamination will cause a yellowish insulator and maybe rust around the end of the plug body. If he finds a discoloured plug at a cylinder in the end 4 pots it may well be a head gasket. If it's discoloured on a plug from the middle 4 pots then its a cracked block.

Thanks. Will let him know. He did think he could see water at the front end of the block. But he saw it on both sides and I would have thought it very unlikely to get a gasket leak on both sides in the same places.
I was thinking it is more likely water from the overflow hitting the fan and spraying back.

Waaait! I had the exact same symptoms. I tied a catch can under the expansion tank overflow and it was filling up every 100km of Sydney driving. I was advised to change the expansion tank cap for a new OEM item, did so and the problem simply went away. The old cap (non OEM) was holding in too much pressure and causing the symptoms. I now drive Sydney to Canberra each week and the coolant level hasn't budged for weeks. Try a new cap first.

Thankyou, that was the sort of suggestions I was after. Might not fix it but worth trying before getting into the expensive stuff.