1998 Pontiac Grand Am gt 3.1L.
Question = my 98 grand am has no heat. The
gauge on the dash works. The engine gets hot,
and the car has not over heated. Is my problem
the thermostat or the heater core?
Several things can cause a no heat condition.
Assuming the coolant is full, there could be air
pockets in the cooling system- this engine is
prone to having leaking intake manifold gaskets,
and/or blown head gaskets. Either can make air
pockets in the cooling system, and the heater core
cannot transfer heat from an air pocket into the
interior. Will not necessarily overheat.

Possibly a plugged heater core not allowing
coolant to flow through it. Possibly a temperature
door problem in the dash not directing air over the
heater core.A bad thermostat will usually either
cause an overheating, or an engine that will not
get up to proper operating temp. If the coolant
temp is lower than normal, then would suspect a
stuck open thermostat.
1998 Grand Am No Heat- Engine Not Getting Too Hot
1998 Pontiac Grand Prix GTP.I have 5 vents on the upper dash
board. I will count them from the passenger side starting with #1.
With the AC on #2 upper dash vent is the only one providing cold
air. I must have a damper not working somewhere. The other vents
1-3-4 and 5 have the same volume of air but it is ambient. #2
provides cold AC air.

Sounds like you may have 2 problems. Two common causes for the
right side vents being cold, and the left side warm....
1) The drivers side temp door actuator motor has failed. This would
cause both right side vents to blow normal, the drivers side vents to
blow warm.
2) Low freon charge. This would cause 1 or both of the right side
vents to blow cool- but not as cold as they should be.

There is no damper between the 2 right side vents. They are from
the same plenum. This is why you may possibly have a low freon
charge, and the drivers side door motor faulty.I would suggest
getting the freon charge checked. Not just the pressure, but actually
remove and have it measured. Even a 1/4 - 1/2 lb can cause right
side to be cool only. Get the freon charge correct, then see is the
drivers side vents are still warm, then you probably have a door
motor gone bad.

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