Without warning, the heater in my 2012 4Runner (88,000 miles) began taking much longer to produce hot air. Ordinarily the cabin would be toasty within a few miles of driving. Now I'm lucky if I have adequate heat after several miles of driving. Believing it was the thermostat, I took it to the Toyota garage. Upon inspection, the technician determined the air temperature from the vents was 150° which is within factory specs. (Of course, by the time I reached the garage 10 miles/20 minutes away it had finally warmed up.) They claim to have also checked a few other possibilities including the cabin air filter. Since Toyota couldn't (or wouldn't) diagnose the problem, I'm at a loss. I'm reluctant to take it back since they already hit me with an hour of shop labor. What say SIGforum? Thanks for any recommendations.

Start with the basics, because you can't assume they did. This may seem obvious, but is there enough coolant in it? If it is low, add as needed, then see if there are any leaks. (One good thing about Toyota's red coolant is that it is easy to spot leaks because it forms a pink crust.) And how long is the engine taking to warm up? The temperature gauge should start to show at least a little within a mile or so of driving, assuming starting from cold. A slightly stuck open or early-opening thermostat will do this. Slow warmup often turns on the engine light and sets code P0128, but not always. A partially clogged heater core is also a possibility, but remote. The hoses leading into and out of it should be about the same temperature.

It has been a month. I'm the only one who's replied to this? Did you find out anything?

If you're willing to troubleshoot, I'd find a friend that has a scangauge or other OBD2 scan device. The temp gauge in the cluster is pretty useless, and the reader will give you actual water temp. If your t-stat is leaking, it will behave as you describe, and take a while to warm up.

Another simple possibility is that air has been introduced to the cooling system.

This acting like a failed thermostat. The fail in the open position. Thus it takes a long time to "warm up".

I suggest you open the radiator cap when the vehicle is cold from overnite. If the coolant is already circulating .... replace thermostat.

Andrew

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Originally posted by egregore:
It has been a month. I'm the only one who's replied to this? Did you find out anything?

Thank you for the follow up. I actually sold the vehicle. In addition to the heater issue, I was also approaching a major service interval as well as addressing some minor paint/rust concerns. With the deal Toyota offered me on a new 2021 4Runner, it made good sense for me to trade up at this time. Thanks to all who responded.