It’s been insanely cold lately, around -30 where I live, and I’ve noticed my truck’s coolant doesn’t seem to heat up to the normal temperature anymore. I think this is why the cab heater isn’t working as well. I’ve attached a picture showing where the coolant temperature is sitting. Any ideas what’s going on?
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I lived in Alaska where it got to -40°F regularly, so I’ve been through this. Without knowing your truck’s details, it could be a stuck-open thermostat or a bad coolant temperature sensor. I’ve dealt with both, and they’re not too hard to fix.
This definitely affects your heat because the heater works by using hot coolant from the engine. If the engine doesn’t warm up properly, your heater won’t either.
Thermostats wear out eventually. Since your cab heat isn’t working, I’d bet it’s not a bad temperature sensor. Thermostats are pretty cheap, and they’re usually not hard to replace depending on the truck.
Driving with a bad thermostat can mess up your engine over time, so don’t let it slide too long.
First thing to check is your coolant level. Cold weather can cause leaks to show up. If the level is fine, then the thermostat is almost certainly the problem.
I wonder if running the heater in those temperatures could keep the engine cooler too? Might be worth considering.
At temperatures below -20, you should consider putting a winter front or some cardboard over part of the radiator to help keep the engine warm.
Could be a thermostat stuck open.
At -30, the engine block might not get hot enough to even open the thermostat. Running the heater cools the engine further, which makes it worse. I’ve seen cases where radiators freeze up completely, and the driver doesn’t notice until the weather warms up and the pressure pops a hose.
If you can get the block warmed up, check the radiator. Feel different areas—warm spots mean coolant is flowing, cold spots mean it might be frozen. If it’s frozen, you’ll need to thaw it out and replace the coolant.
If the radiator is warm but the engine still won’t heat up, the thermostat is likely the problem, and a coolant flush might also help. Be sure the new coolant isn’t too diluted; get a tester from an auto parts store to check.
Depends on the truck. My Silverado takes 10–15 minutes of city driving in -20°C to open the thermostat, and that’s normal. But I also have a tiny Subaru Kei truck, and in -30°C, if I sit at a red light for more than 30 seconds, all the heat disappears, and you can literally watch the temperature gauge drop back to cold.
If your truck is taking longer than usual to warm up, or it’s acting out of the ordinary, replacing the thermostat is usually the easiest and cheapest first step.
Because it’s freezing cold out??