No heat and overheating

TERRY LECHLITNER

MEMBER
2000 PONTIAC MONTANA
3.4L
6 CYL
2WD
AUTOMATIC
212,000 MILES

I've only had the van about a month. The water pump was definitely bad. I changed it, filled up the antifreeze. With the radiator cap off n engine running you can watch the fluid raise and lower, that being said it's never had heat since I bought it. It appears that the antifreeze is flowing so I'm not believing it's the thermostat. I've never let it get to the point where it was losing fluid from overheating but the gauge will jump almost to the red about ten to fifteen minutes after starting, the warning light will come on. I haven't tried to pull the HVAC fuse/breaker yet nor checked the heater core. The weather isn't cooperating for me. I've wondered if they previous owner didn't bypass the heater core if it went bad in warm weather but as I'm not familiar with this van or the 3.4l for that matter I figured I'd see what suggestions people have.

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,320 POSTS

Hi Terry and thanks for using 2CarPros.

The first thing (when the weather is better) is follow this link. It discusses the most common reasons the heater won't work and how to check them.

https://www.2carpros.com/articles/car-heater-not-working

Also, if you look at picture 1, it shows where the heater core hoses connect to the core. If the core is bypassed, the hoses most likely be missing.

IF you determine the heater core is bad, here are the directions for replacing it. Here are directions in general showing how it is done:

https://www.2carpros.com/articles/replace-heater-core

Heater Core Replacement
Vehicle Heating and Air Conditioning Heater Core Service and Repair Removal and Replacement Heater Core Replacement
HEATER CORE REPLACEMENT
Heater Core Replacement

Tools Required

J 38185 Hose Clamp Pliers

Removal Procedure

1. Drain the cooling system. Refer to Cooling System Draining and Filling (Static Fill LZ9) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (Vac-N-Fill) (See: Cooling System > Removal and Replacement).

See Picture 1
2. Disconnect both of the heater hose clamps (1) at the heater core using the J 38185.
3. Remove the heater hoses from the heater core (2).

Important: Cap off the heater core inlet and outlet pipes to prevent coolant spilling inside of the vehicle.

4. Cap off the heater core pipes.
5. Remove the heater core cover. Refer to Heater Core Cover Replacement (See: Heater Core > Removal and Replacement > Heater Core Cover Replacement).

See Picture 2
6. Remove the heater core pipe clamp screw (1).
7. Remove the heater core (3).

Installation Procedure

See Picture 3
1. Install the heater core (2).

Notice: Refer to Fastener Notice (See: Vehicle > Vehicle Damage Warnings > Fastener Notice).

2. Install the heater core pipe clamp screw (1).

Tighten the screw to 1.2 N.m (11 lb in).

3. Install the heater core cover. Refer to Heater Core Cover Replacement (See: Heater Core > Removal and Replacement > Heater Core Cover Replacement).

See Picture 4

4. Install the heater hoses to the heater core (2).
5. Reposition the heater hose clamps (1) to secure the hoses using the J 38185.
6. Fill the coolant. Refer to Cooling System Draining and Filling (Static Fill LZ9) (See: Cooling System > Removal and Replacement)Cooling System Draining and Filling (Vac-N-Fill) (See: Cooling System > Removal and Replacement).

___________________________________

If you find the core is good, the next check is the blend air door. Here are directions for replacing it.

Air Temperature Actuator Replacement (Single Zone)

Removal Procedure

See Picture 5

1. Remove the driver side knee bolster.
2. Locate the air temperature actuator (6).
3. Disconnect the air temperature actuator electrical connector (7).

See Picture 6

4. Remove the air temperature actuator bolts/screws (1).
5. Remove the air temperature actuator (2).
6. Remove the air temperature actuator lever (3), if necessary.

Installation Procedure

See Picture 6

Important: The actuator lever can only be inserted into the door one way.

1. Install the air temperature actuator lever (3), if necessary.
2. Install the air temperature actuator (2).

Notice: Refer to Fastener Notice (See: Vehicle > Vehicle Damage Warnings > Fastener Notice).

3. Install the air temperature actuator bolts/screws (1).

See Picture 6

Tighten the bolts/screws to 1.2 N.m (11 lb in).

4. Connect the air temperature actuator electrical connector (7).
5. Install the driver side knee bolster.
6. Re-calibrate the actuators. Refer to Actuator Recalibration (See: Vehicle > Programming and Relearning).

Let me know if this helps or if you have other questions.

Take care,
Joe

Images (Click to make bigger)