right the cap is leaking not allowing the system to pressurize. The efficency of the cooling system can be reduced up to 50% by lack of proper pressure. Also, coolant can locally boil in hot areas of the engines like the cylinder heads.

A very likely possibility is that coolant did locally boil casuing some coolant to vaporize and some of the vapor got trapped in the engine, while the rest was being vented out the cap hence your burning coolant smell. This entrapped vapor, when you shut down the engine, it was hot and as all gasses do it was expanded. Its possible that the cap's check valve that does not allow anything to get into the system is working fine, so as the engine cooled and the gas contracted it created a vacuum and because the system is sealed the coolant was not able to overcome and flow into the empty space, but as soon as you poped the cap the coolant flowed right in.

My suggestion, re-fill the system with the porper mix ratio of coolant and water. Then with the cap off allow the engine to run until fully warmed up and the thermostat opens. Once the thermostat is opened set the engine to a high idle 1500 to 2000 RPM with the heat on and watching the temperature guage to avoid overheating this will allow the water pump to quickly circulate to try and expell this vapor from the engine. I wouldn't be suprised if you saw several bubbles flow out from the egnine.


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