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Well my upper hose is leaking on both ends, even with additional span around it.

So I wen to check maybe there's some air around thermosat so I started the car with the radiator cap off. Car reached usual operating temperature (just a bit above middle) and stayed there. Radiator fan didn't start (I rarely notice it working anyway) and the coolant start evaporating (temp needle was still a bit above middle) so I turned off the engine.

Does anyone know what's going on??

DId you just drain all ur rad fluid recently? And did a change? Because if you did, it was just refilling the Heater lines and all the misc lines that need to be filled, Is it Antifreeze or water? water tends to evaperate a bit quicker.

If not you have a minor leak somewhere..

I'm not sure I understand what the problem is.

You know that your upper rad hose is leaking, and you're wondering why you're losing coolant?

Perhaps your concentration of water is high in your coolant, and the mixture has a low boiling point.

I put a new radiator and after a while I replaced water with coolan t mixture which is now leaking on the upper hose.

I've strongly tightened the hose but it's leaking on the ends.

So I thought pressure is too high because there might me some air around thermostat or because of worn valve cover gasket.

I was running engine on idle and a bit reving it, radiator cap was off, temp gauge was constantly little above middle, coolant started evaporating above radiator cap like I'm boiling eggs, fan didn't start.

So my questions are:

-Why temp gauge doesnt go higher than usual position (a bit above the middle)?

-At what point does the fan start (2/3 on the temp gauge or what)?

-Was the temperature in the system too high when coolant mixture started visibly evaporating (probably around 110C)?

It started leaking around radiator cap now What could be causing that? Water pump has been replaces year ago.

Maybe your rad cap isn't allowing the pressure release that it should be. Try a new cap, they're cheap. Perhaps your coolant overflow tube is clogged or piched. I would think that before bursting out through your upper rad hose, the coolant would run to your overflow tank, it is the path of least resistance.

My rad fan rarely ever comes on, and I know that it works. My engine rarely goes anywhere near mid temp. Thermostat and coolant sensor are okay.

Thanks man, I'll try that. I didn't know cap has spring that regulates pressure, I though it is only a cap

It was the cap

Excellent.