07 Toyota Sienna Heater takes 20 mins to blow hot

Question

The dash temp gauge reads in the middle between hot and cold within a few minutes of running. However, it takes about 20 minutes for hot air to come out the front heater vents when the heater is set to maximum heat and the fan is on.

I noticed that the coolant was low so I filled the coolant using the reservoir up to the "full" line. I tried running the van again and took it back up to normal operating temperature. No change (still no heat). I then located the heater core inlet/outlet tubes. The easiest access to them as far as I can tell is from inside the van, they come in to the right of the gas pedal. I touched them, one was very hot, the other was quite hot but I could hold on to it without getting my fingers burnt.

Given this, what should my next move be? Take it to the mechanic? :)

Update: I added even more coolant from the radiator (after waiting until it was cold). It took quite a bit. It has been pointed out to me that I have a coolant leak that I need to get checked out. After adding the coolant I again ran the van, sitting in the driveway and revving the engine to about 3000 rpm for a few minutes. The temp gauge read normal (midway between C and H) and the heater core pipes were both very hot to the touch. I turned on the blower and initially it came out hot but then went back to being cool again after a short while. That was last evening. However, this morning when I took the van to work, the heater blew hot air quickly, as it used to. At this point I'm not sure if I'm dealing with an intermittent problem, or if it's working properly now.

Another update: heater is still working fine. Had to add yet more coolant though as reservoir still showed significantly below "full" level. This morning the check engine light came on. Taking the van to the mechanic's to see what's going on (might be coincidence, don't know).

Answer 1

Things may have changed, but I had this happen to my '94 Toyota Pickup. It was a bad thermostat. On that model it was built into the radiator cap. Basically, it gets stuck open and takes longer for the engine to heat up enough to operate the heater.

Cold engine test: Start the engine. Time how long it takes the engine to warm up enough to produce heat when the heater is turned on.

If it takes more than five minutes for the heater to produce heat, it is a sign that the thermostat is stuck open, allowing all the coolant to flow all the time. It takes a good deal longer for the engine to warm up.

Removing and Testing the Thermostat

If you are still unsure whether the thermostat is stuck, perform the following procedure to get an accurate diagnosis.

1. Disconnect the negative battery cable.
2. Drain some of the coolant (a gallon should be enough) so the fluid won't pour out when you perform the next step.
3. Remove the upper radiator hose.
4. Remove the thermostat housing.
5. Remove the thermostat.
6. Locate and write down the temperature stamped on the lip of the thermostat.
7. Fill a pot with cold water and a thermometer and place on a stove burner.
8. Place the thermostat into the cold water.
9. Turn the burner on.
10. Watch the thermometer. When the temperature rises to the number you recorded in step #6, the thermostat will start to open. If it does not, or if it doesn't open until reaching a different temperature (hotter usually), then the thermostat is bad and should be replaced. If it opens at the designated temperature, then the thermostat is just fine.

source

These instructions are kind of generic. If it's anything like my old truck, the thermostat is built into the radiator cap and it's trivial to remove and test. Check your manual to find its location.

Answer 2

After a visit to the mechanic this turned out to be due to a cracked radiator. That caused coolant leak which led to heater not working. Will replace radiator. Check engine light that came on seems unrelated to this issue.