Have a Toyota Camry 4cyl. It got hot so I stopped and let it cool down. Turned it back on and added water it ran for few miles got hot and popped reservoir cap open.
I thought the thermostat was bad so I changed it but now wont start at all after getting hot and dying. No water in oil check engine light is on. Water will not go into engine just keeps pushing back into reservoir.
Does not sound good, probably did some internal engine damage. Get a cooling system pressure test AND a cylinder compression test which should tell you I there is internal damage like a blown head gasket.
You should also check the radiator for a restriction that is stopping coolant flow and thus backing up into the reservoir tank. Rust forms at the bottom which can not be flushed out, a new radiator is the answer.
If you get the cooling system pressure test done (which is what you should do first) and the compression on the engine is ok, then try this head gasket sealer which I talk about in the video below.
It really does work, but if the engine damage is so severe the engine will not stay running or drive it might be too late. Pulling the cylinder head and doing a valve job, cylinder head resurface and head gasket replacement might be your only option.
When you see back pressure (coolant coming out of the radiator or pressure inside the reservoir) it is usually because there is a tear in the head gasket inside the engine. This torn gasket is allowing engine compression from the cylinder to get into the cooling system.
You usually also see white exhaust smoke, due to coolant leaking into the cylinder and the engine and spark plug tying to burn it, which it can not so it comes out the exhaust in a cloud of white smoke.
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