Problem with my heater

Maintenance/Repairs
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1

I’m having a problem with my truck’s heater. It puts out hot air when the temp is above (roughly) 20 degrees outside. When it gets very cold (right now, it’s -5), the heater blows only slightly warm air. This happened last winter, however, it was only really cold for about a week. When the temp hung around 20-25 at the coldest, I didn’t have any problems and forgot to fix it. Any help is appreciated.

2

What year, how many miles? When was the last time the cooling system was checked? When was the last time the coolant was flushed and filled? With a new thermostat and radiator cap?

The symptoms you describe are typical for a thermostat that is failed open. The coolant on cold days gets cooled too much from the radiator, and keeps the engine too cool as well. A new thermostat will fix this. Couple that with a coolant flush-n-fill and a new radiator cap should keep it fixed.

3

1999 - 84K. I’ve had it since 2006. I’m not sure when the last time the cooling system was checked / last time the coolant was flushed. If was filled last winter. I think the thermostat is the original.

I’ll replace the thermostat and flush/fill the coolant and see how it goes - thanks for the help.

Also, my “check engine” light came on the other day. I took it to Autozone and they hooked it up to their handheld. It said that plugs 1,2 and 3 were misfiring (all 3 on the passenger side). I haven’t noticed any power issues / backfires / chugging, etc. Do you think this could be a serious issue? The plugs were replaced in June 2009.

Thanks

4 
[i] my "check engine" light came on the other day. I took it to Autozone and they hooked it up to their handheld. It said that plugs 1,2 and 3 were misfiring (all 3 on the passenger side).[/i]

I would consider new wires for the ignition. A set of OEM wires (not the fat colorful fancy ones for the hot rods) would be a good idea. Wires have a limited live and 100,000 miles range is certainly not a bad time to replace them.

I don’t know the B4000 but some cars have some common parts for each side, that might be worth checking. For example if they each have a coil shared on that side, then that coil would be suspect.

5

The super cold may have an effect on the aging vacuum operated water valve you’ll find in the heater hoses near the firewall.