Heat Problem (Addendum)

Definately sounds like a TStat. davidj92

Thermostat is the first thing to check, since you said the temp gauge doesn't hit the halfway point. Easy and inexpensive job.

Then worry about water flow through the heater core - check that the heater control valve opens like it should, hoses are clear and not collapsed internally or kinked at bends, backflush the heater core with a garden hose to make sure it isn't plugged up.

Water pump next - when they're worn, the impeller rusts away and they don't give the flow volume. Might be enough flow to keep from overheating, but not enough to push through the heater too. But changing water pumps can be complicated.

Last resort is swapping out the heater core for a new one, because on most cars and trucks it's a Gold Plated SOB of a complex job.

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