I just had the coolant replaced on my 2003 Matrix (33k miles) and I noticed that when I drive my car the heater air is lukewarm for about 3-5 minutes and then abruptly it gets hot. I'm not 100% positive but I think before I had the coolant replaced, the heater air didn't take *that long* to get hot. If this is true, I'm guessing that somehow the thermostat is taking longer to open up. How could changing the coolant have affected this? Could the mechanic have screwed up something? (I went to an independent garage).
Air in the cooling system is a possibility that is easy enough to check. The next time you park the car for 4 hours or so, turn the heater control all the way to hot a minute or two before you turn off the engine. After the engine has cooled, look at the coolant level in the overflow bottle. It should be filled to the "cold" mark. If the radiator has a cap, remove it and take a look inside the neck. The radiator should be filled to the top. Do not attempt to remove the radiator cap while the engine is warm or you may get serious burns!
The heater is basically a mini-radiator in the passenger compartment, and instead of getting rid of heat in the outside air like the radiator does, the heater core passes its heat to the air flowing into the passenger compartment. The heater control valve controls the amount of coolant flowing through the heater core. When you start a cold engine, the coolant is the same temperature as the ambient air and the rest of the car. It will take a few minutes for the engine to warm the coolant to 140 degrees or so and open the thermostat, allowing the coolant to flow through the radiator. It will actually take a little longer for the coolant to reach operating temperature if it is flowing through the heater core because it is trying to give what little heat is built up to the passenger compartment.
IMO, 3 minutes from cold startup to heat flowing from the heater core is not unreasonable.
It really depends on the car. I have a geo prizm (corolla) and it heats up in about 3 minutes (the gauge does at least). I've had other cars that took a lot longer, even brand new ones. I guess the capacity of the coolant system also plays a part in it.
I did what Ray outlined, and there was no coolant in the overflow bottle nor inside the neck. I filled the overflow bottle to the "full" mark and repeated the test the next time I parked the car. The coolant had gone done a little less than a pint. So all in all I think it was underfilled by about
1/2 gallon of coolant by the mechanic. I had driven my car that way for about a week -- could that have done any damage to my car? (I doubt it; but thought I'd ask).
If they flushed and drained the cooling system and didn't 'burp' the heater on the final fill (some cars need this, most don't) it would take more coolant over the next few days and warm-cool cycles as the air worked it's way back to the radiator and out. But then the level in the recovery tank should stabilize.
As long as there was enough coolant to circulate into the radiator, it shouldn't hurt the engine.
Try that in August when it's hotter than hell and you are pushing the engine, and the results might have been a bit different - you want to check the coolant level daily (as well as everything else under the hood) for a few days after doing any work on the car. Things don't always leak immediately.
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