Questions and Answers

Nissan Maxima Low Heater Output Q. Hello: I recently, about six weeks ago, purchased a 1990 Nissan Maxima with a 3.0 liter engine, automatic transmission and 71,000 miles. The problem is the cooling system. I live in Illinois and it was quite cold, near 10°, when I bought the car. I was told that the heat did not work well, that it needed a thermostat. The car only provides heat while I'm driving and then it doesn't ever blow "hot", just luke warm.

The heater controls seem to work fine. If I'm at an idle it blows ice cold. Also, if I let it idle for more than a few minutes I notice the temperature gauge go through the roof, all the way "hot", still no heat at idle. A couple of minutes after the gauge pegging itself it comes back down into the normal range by itself.

The seller is a trained mechanic and he says the gauge is wrong. I want to believe him but I don't know that a bad thermostat will do this. After reaching operating temperature, if I open the radiator cap there is pressure there. He says he's back flushed the system. The weather the past few days has been in the upper 30's/lower 40's. Still no improvement. Can you help?

Thanks,
Don

A. A bad thermostat could cause this. If it has to get very hot to pop the spring and then stays wide open it may cause the symptoms you describe. However, before the spring pops open, you will have good heat from the HVAC system.

I think the problem is an air bubble in the cooling system. The Nissan Maxima has always been a tricky cooling system to bleed air out of.

The problem is the heater core is above the filler neck and does not fill with coolant, causing low or no heat. What we have to do is get the filler neck above the heater core. This can be a bit tricky and I'm not sure you will be able to do this at home.

Since you probably need to replace the thermostat, I would do that before going through the bleeding procedure. No sense going through it twice.

BLEEDING PROCEDURE:

1. Lift only the front end of the vehicle, so that the bottom edge of the front bumper fascia is about 990 mm (39") above the ground. Make sure that the exhaust finisher is not damaged by contact with the ground. Raising the front end of the vehicle lowers the heater core location below the radiator inlet opening.

NOTE: If starting with an empty heater system (no coolant), the system should be filled with coolant with the front end already raised.

2. Make sure the engine is cool. Remove the radiator cap and add coolant as required so that the coolant level comes up to the radiator filler opening.

3. Turn the engine ON and run it at aldl.

4. Move the temperature control lever to the "full hot" position on vehicles equipped with a manually-controlled air conditioning system or 85° F for an Automatically Controlled air conditioning system.

5. Select "Foot" mode for vehicles equipped with manually controlled air conditioning systems. Make sure the air conditioner is OFF. Select "FOOT & ECON" mode for vehicles equipped with an automatically controlled air conditioning system.

If the A/C compressor is left ON, the engine fan runs continuously. This keeps the engine temperature low and does not allow the thermostat to open. Also, if the A/C compressor is left OFF, the engine fan will come ON when the thermostat opens.

6. Increase the engine speed to about 1,500 RPM and hold. Decrease the engine speed if there is excess coolant spillage from the radiator inlet opening. Place a small object, for example a folded piece of paper, between the throttle drum stopper and the intake manifold to hold the engine speed.

7. Watch for air bubbles coming out of the radiator inlet opening to make sure the air bubbles are being purged. Add coolant as necessary to maintain a full radiator. The coolant level, as seen at the radiator inlet opening, will drop when the thermostat opens.

Do not add coolant when the thermostat is opened as the radiator will overflow when the thermostat closes. When the engine fan is running it is a good indication that the thermostat is in the "open" position.

This procedure must be run for at least 30 minutes or until large air bubbles (larger than 5 mm diameter) stop coming out to ensure that all air bubbles are purged from the cooling system. This usually requires the thermostat to open on two separate occasions.

8. After 30 minutes, there still may be tiny bubbles (less than 5 mm diameter) coming from the radiator filler opening. It is normal for bubbles of this size to continue, so, it is not necessary to continue the procedure until the small bubbles stop.

9. After the bleeding procedure is complete, remove the small object inserted between the throttle drum stopper and the intake manifold and return the engine to idle. Add coolant to fill the radiator and immediately place the cap back on the radiator.

10. Slowly lower the front of the vehicle to the ground.

11. Add coolant to the reservoir tank until the level reaches the "MAX" mark. Remove the screw which secures the coolant reservoir tank, and with the return tube attached, lift the reservoir tank above the radiator. Tilt the reservoir tank so the return tube is at the lowest point. Squeeze the return tube to purge the air trapped in the tube. When the return tube is filled with coolant, return the reservoir tank to its proper location.

12. Shut the engine OFF. The engine should be allowed to cool down. If the system is not completely filled, some coolant will be sucked back into the engine. Additionally, the procedure should be repeated at least once to ensure that all of the air has been bled out of the system.

If this is something you won't be able to do, just print out the procedure and take it to your regular mechanic.