My son’s 2007 Focus, 160,000 miles was losing a bit of water and overheating. Since he could never see exactly where the water came from, he replaced the hoses, the water pump, and the thermostat. Verified the fans work as they’re supposed to. He let the car idle for 30 minutes, temperature normal and no leaks. Took it on a trip and it started running hot. He pulled over, loosened the radiator cap, and the temperature went back to normal. Drove the rest of the way with the cap loosened and no problem. Got home, tightened the cap, and took a test drive. Overheating again. We have no clue what’s going on.
Check the oil filler cap for a chocolate shake looking residue. If that is present you have coolant leaking internally due to a head gasket breach.
One thing that can cause an engine to overheat if the vehicle has an automatic transmission is a transmission that’s overheating.
The transmission fluid cooler is located inside the radiator.
That means if the transmission is running hot, it can cause the engine to run hot.
Tester
Thanks. We’ve checked that. Nothing in the oil, and the coolant mixture is clean, too. And this is a 5 speed, not an automatic.
Could be a blown head gasket.
Has he checked the water outlet?
If the engine is only overheating on the highway you might check to see if the lower radiator support air deflector is missing.
Those frequently get knocked off by potholes, road debris, or soon to be deceased critters.
Lack of a deflector will not cause overheating in city driving.
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Radiator overflow tank is getting hot, as are upper and lower hoses. So the water is circulating OK. About the only thing we haven’t changed is the cylinder head temp sensor, the one in the center of the valve cover.
I wonder if it’s worth topping the system off, then getting a pressure test kit…you could pressurize the system and see if there are any external leaks anywhere. Some UV dye can assist with this too. The water outlet was the only major issue I had with my 09 before it got totaled around 215k. I replaced the outlet on it twice. (The first time I wish we had pressure tested first…I assumed it was the water pump and didn’t test the system. Well, on the 09, the water pump is not only metal (and was fine!), but a royal PITA to get in and out. Once we reinstalled the water pump, we got a pressure tester and it was quickly and apparent that the problem was the water outlet).