I have a 2004 Toyota Corolla, with about 175,000 miles, and recently the heating system has been acting up. About three weeks ago the heat started to be slow coming, even when the engine was warm, but after a bit of driving it would kick in. The blower would work the whole time, but it would blow cold, instead of hot. However, no even that amount of heat has subsided, and the blower only blows cold air.
On top of that, within the last week or so the engine has begun to almost overheat early in driving, but settles down a bit after driving a few miles.
Believe it or not, there is a possibility that the OP’s engine is running with antifreeze/coolant that does not have sufficient protection against low temperatures. This can result in icing in the cooling system that can actually lead to overheating as well as poor heater performance. This may sound counter-intuitive, but I have seen it.
I strongly suggest that the OP have the coolant changed a.s.a.p., if it has not been done in the past couple of years. If that does not work, then look to the thermostat and/or the heater core as the source of the problem.
The engine overheating is the more seious of the two problems. I expect if this is solved, the other will be also. As mentioned above, sort of sounds like the coolant may slushing/freezing up, either that, or there is air in the system. As mentioned above, if OP lives in an area of freezing temps, the first thing to do – straight away – is make sure the coolant in the radiator (not just the overflow tank) is up to the normal fill level, and at the same time have the coolant checked with one of those temperature rating gadgets, to make sure it won’t freeze at the temperatures the car is being subjected to when parked at night.
If the coolant rating is ok and is full … and the coolant is less than 3 years since last change … hmmm… my first guess would be a faulty radiator cap, 2nd would be a faulty thermostat, and 3rd would be a sticking water pump.
Re heater issue: OP could feel both hoses to the heater core (they go through the fire wall). When the heater is on full and the heater fan is on, one hose should be quite hot, and the other only warm.
OK. Thank you all. I will check the coolant, which hasn’t been changed ever, as my first step. If that doesn’t resolve it, thermostat is the next step?