P0115 and failed coolant reservoir tubing

[Vman123]

I searched other threads to see if this interesting problem has happened to anyone else. 2001 4 cylinder with 100k miles and good maintenance record. Belts and water pump changed last year at 90k. Lent the car to family member. 3 days later they say check engine light and distinct smell of burning oil. No comment on engine temperature gauge and really cannot recollect. They drive for about 30 miles before I can take a look.
I connect scanner and get p0115 - coolant system problem.
I open hood and note the coolant reservoir is way above full line almost to cap. I open it and the rubber pipe that connects to the cap and dips to the bottom has disconnected. I reconnect and drive for 5 minutes. Temperature huge shoots up to 'H' and I turn of.
Pop open hood and reservoir is still full. I open radiator cap and look inside- no coolant. I close it back and continue to just look and then in a few seconds the reservoir starts emptying till it is empty. I restart the car and the temperature guage stays in the middle. Get to a service station, change oil ( assuming extreme heat had burnt some of) and filled up coolant.. 100 plus miles and still running good.
1 - why did the pipe in reservoir disconnect.
2- after reconnection why didn't coolant suck back into radiator?
3- why didn't engine seize?- this is Texas heat wave weather.

[JohnGD]

The hose under the cap is interference fit. There is no pressure acting on the hose so it shouldn't blow off. If the fit tight? Maybe the hose aged too much.

If air got into the radiator there may not be enough vacuum to suck much coolant back from the reservoir. You may want to borrow a cooling system pressure tester from Autozone's free loaner program. The radiator cap should be checked so the vacuum return valve works and is not plugged.

See OEM27049:
http://www.autozone.com/autozone/ino...tingAndCooling


Just keep an eye on the head gasket and water pump shaft seal. These tend to go after an overheat.

One guess is the hose under the reservoir cap fell off. And then the radiator was just sucking air back into the system. When things cooled down the system is then low on coolant and the vicious cycle continues.