I did a full 100k service on it almost 12 months ago to the day. used all genuine Nissan parts. was all sweet up until a couple of weeks ago. Ill check with the top hose off tomorrow. When it was running, I think warm, it just like bubbled over, no real force like it was going into the air.
Head gasket.... they can leak only one way. Combustion into the water jacket is probably the most common one. When mine failed like this, it wouldn't show up on a pressure test. Fifteen pounds is a lot less that what is created within the combustion chamber. I know this one from experience.
The overflowing could be bubbles. We started the car from cold last night. It had enough pressure after running for 30seconds to make a mess when the cap was taken off.
I had a similar issue in my car, took the shroud off today and realised that the bottom of the rad core was leaking and the water was being sucked onto the front of the motor by the clutch fan.
That volume would be more a haemorrhaged gasket than a leaky one wouldn't it? So you would assume water would be making it into the exhaust. Was it filled to the neck before starting? Possibly a stalled pump still? Did you try spinning it by hand/notice anything when you took the fan off?
A mechanic friend said he could lend me his gasket/coolant test kit on friday, I'll pm you my phone number if you want to set something up for friday arvo or saturday at some point
I managed to get the thermostat out without undoin the belts. I might loosen off a belt and check. Friday night sounds good to me.
I note that you have already pulled the overflow tank and cleaned it thoroughly ? I had a similar problem and it turned out eventually to be a small pellet of crap that had built up like a pearl and was sitting in the bottom of the tank. From memory there is a small channel at the bottom and the pellet was stuck in there. I had to mechanical remove it. When water enters the tank it pushed the pellet away and everything was fine. When water wanted to siphon back into the radiator the pellet moved forward and acted as one way valve. So eventually depending on how often I drove and how long the radiator would empty and engine overheats. My first time inspection of the tank didn't reveal the pellet because the tank was so dark and full of crap and the pellet the same colour that I didn't see it. The next time I found it though. I suspect that a good rinse may only peel a layer off the pellet and it will build up again which is why there was a period between the first time the tank was off and the next overheat. I found it hard to believe but when you have bits of pellet in your hand its hard not to. No overheating after that.
