No heat issue, and the coolant *is* properly bled

[sofloe53]

Having an issue where the car isn't producing much heat. Coolant is properly bled, where with the expansion tank cap off, water is returning back into the tank. Holds temp well and I don't suspect an air bubble in the heater core. All I get is lukewarm heat with the heat settings on their hottest. Could it be the heater modulating valve?

[andrewwynn]

Almost always that is a problem with thermostat not closing complexly. Use hidden menu to read the engine core temp. If the engine runs around proper temp, then it's likely the heater core valves but since there are two it's not very likely both would fail.

Foxwell will report temp of the heater cores and state of the valves so if you can read those values, that's even better.

Next things would be if the vanes inside the AC ducts are stuck on outside air you won't get much heat.

The outside mix dial in the dash should give you a full range from hot to outside, so if the cables broke it can get stuck on outside air.

The non-gauge for temp on the dash is nearly useless it will not report anything useful for diagnostic testing other than a small hint of taking longer than normal to get to temp. If it hangs in the blue zone for any amount of time the thermostat is Misty likely the culprit

[sofloe53]

Originally Posted by andrewwynn

Almost always that is a problem with thermostat not closing complexly. Use hidden menu to read the engine core temp. If the engine runs around proper temp, then it's likely the heater core valves but since there are two it's not very likely both would fail.

Foxwell will report temp of the heater cores and state of the valves so if you can read those values, that's even better.

Next things would be if the vanes inside the AC ducts are stuck on outside air you won't get much heat.

The outside mix dial in the dash should give you a full range from hot to outside, so if the cables broke it can get stuck on outside air.

The non-gauge for temp on the dash is nearly useless it will not report anything useful for diagnostic testing other than a small hint of taking longer than normal to get to temp. If it hangs in the blue zone for any amount of time the thermostat is Misty likely the culprit

Just took a look again and found that the hose running from the bottom of the expansion tank to the firewall is cold, while all other heater hoses are warm. What does that signify?

[andrewwynn]

"warm" or operating temp? If the heater core hose is cold implies the heater valves are shut but can mean other things. Example: wife's car output cold air at idle but warm air at 2000+ RPM because the aux water pump was shot.

Get the core temp reading using a scanner or the OBC hidden menu and confirm the engine is getting to 90C. The coolant can be quite warm to touch yet pointless to heat a car and the heater valves won't open until the coolant temp reaches a minimum.

If the coolant temp sensor is broken it can report a much colder temp than actual and never open the valves.