2009 Forester XT overheating at slow speeds
A little background first just in case it could be relevant. I had a catalytic
converter go bad/clog up and that did cause the engine temp light to flash
red briefly one time. Got the cat replaced and everything seemed fine for
several months. I just drove over 300 miles from OKC to Lawrence KS
without any issues at all until I arrived in Lawrence and slowed down to city
street speeds. Red temp warning lamp starts flashing. I opened the OBD
Link app on my phone and there are two different temp readings: Engine
Temp, and Coolant Temp. These appear to be different sensors because
Coolant temp reads fine at ~190F, but engine temp is ~220-230F. I stopped
the car immediately. Opened the hood, and this car has two pressurized
caps for the coolant. One on the radiator, and one on a small tank by the
turbocharger. The cap on the tank near the turbo (which has a lower
pressure rating) is burping fluid into the reserve tank (non-pressurized) which
has overflowed. I did not notice anything indicating coolant in the oil or oil in
the coolant (dipstick and under the fill cap looked fine as did the coolant in
the reserve tank). I let it cool and drove to an auto parts store, then to my
hotel for the night. The next day I put almost half a gallon of coolant in the
car. Drove a few miles around town and everything was fine. Got on the road
back to OKC and I am watching the temps like a hawk. No overheating at
highway speeds, but as soon as I pulled off for gas and a bio break, the temp
starts going up over 200F quickly, but I shut off the car before the light came
on. Got back in the car and as I accelerated on to the highway, the red
warning light blinked for about 5 sec, then stopped and temps were fine the
rest of the way home until I got off the highway again. Again, as soon as I
started slowing down, the temps quickly rose above 200F and got up to
almost 240F before I could get somewhere to stop the car and shut off the
engine. Again, the reserve tank has overflowed because the cap near the
turbo is releasing coolant. The upper radiator hose is obviously hot, but the
lower one barely feels warm at all. Could my radiator be clogged? Could the
cap by the turbo be bad and releasing coolant which causes the engine temp
to overheat while the coolant temp still appears fine? I do not THINK it is the
head gasket because there are still no indications of coolant and oil mixing in
either the engine or the radiator and overflow tank, but I do not know what
else it could be. Please help. Thank you.