Got home from work and decided to finally look into something I’ve wondered about for a while: how effective is my heater, really? It’s been cold lately, and while I can tolerate just about anything, we’ve got a Big Bend trip coming up and I’d really like my wife to be comfortable. Freezing in a lifted 4Runner for ten hours isn’t exactly romantic.

So I figured I’d do a quick check. I shot temperatures at the inlet and outlet of the heater core to get a better picture of how the system was actually performing. Turns out that was a great idea—because while I was messing with the heater control valve, it literally crumbled in my hand.

Coolant immediately started pouring out, and I shut the truck off as fast as possible while mentally running through worst-case scenarios. After a quick assessment, I realized I could bypass the valve entirely. I removed it and ran the inlet hose straight to the heater core so I could at least drive the truck without dumping coolant everywhere.

That solution worked… but there was no way I was trusting it for a ten-hour road trip. So, unfortunately, we took my wife’s car instead—which means we missed out on some truly epic 4Runner-in-the-desert photo opportunities.

A few weeks later, the replacement valve finally showed up. I got it installed pretty quickly, and everything went back together without drama. Hopefully this one lasts another 20 years and I never have to think about it again.

As for the original question—the heater itself is doing just fine. The heater core showed about a 30-degree temperature delta, and vent temps were over 100°F. There is some variance between vents, though. The passenger-side vent was about 20 degrees cooler, which I’m guessing is due to worn plastic air diverters somewhere deep behind the dash.

And honestly? I have zero interest in pulling the entire dash apart to fix that. It’s going to take something far more urgent than a slightly cooler passenger vent for me to willingly open that can of worms.

For now, the heat works, the coolant stays inside the engine, and winter trips are back on the table. I’ll call that a win.