No heat in a Michigan winter and an engine that runs hot are the same system failing in two directions, so both get the same set of tests.
At a glance
- Cold air from the vents is often low coolant, not a bad heater
- A stuck thermostat can cause no heat or overheating
- An overheating engine should be shut off, not driven home
- We pressure test rather than guess at where it goes
Your cabin heat comes from engine coolant. That is why the two problems are one problem. If the level drops, the heater core starves before the gauge ever moves, so cold vents are often the first warning you get.
A thermostat that sticks open never lets the engine warm up, so you get lukewarm air and worse fuel economy all winter. One that sticks shut cooks the engine. Same part, opposite failures.
Overheating is the one to take seriously. An engine run hot for ten minutes can warp a head and turn a $200 repair into a $3,000 one. Pull over, shut it off and text us. That is cheaper than getting it home.
We pressure test the system cold to find where it leaks, check the fan and the thermostat behavior, and test for exhaust gas in the coolant when a head gasket is on the table. Guessing at cooling parts is how people replace three of them.
Common questions
Why is my heat cold only at idle
That points at low coolant or weak flow through the heater core. Both are testable and neither improves on its own.
Can I just keep topping up the coolant
It is going somewhere. A slow leak becomes a roadside stop, and coolant in the wrong place ruins engines.
Is stop leak a real fix
It can buy a few weeks and it can also block a heater core for good. We would rather find the leak.
Tell us what the car is doing
Text a photo and your location. You get a real answer from a real person, whatever the hour, and a written quote before anybody touches anything.