Questions and Answers

Quest Heater Q. 1993 Nissan Quest GXE, 6 Cylinder, 137,000 miles, Automatic transmission, front wheel drive, power (steering, window, lock, window), front control heater, rear control heater, A/C.

Car condition: The engine coolant temperature gauge is at normal or slightly below it. The coolant looked murky and radiator cap is rusty.

Problem: The front control heater dial is turn to maximum but the air come out is cool. On the contrary, the rear heater producing decent heat when rear heater control dial turned to maximum. Are the thermostat, heater core plugged, heater control valve, front control dial or heater core plugged that are causing the problem and how do I diagnose these? Could you please help me.

Work performed try to fix the problem: Yesterday, I flushed the radiator and replaced with new coolant.

A. The first thing I would look at is the heater control valve. If it is not opening you have a problem with the valve or the cable linkage between the temp selector and the valve. What you need to do to check this is to get under the dash on the right side and visually check to see if they it is opening and closing and that the cable itself is moving correctly. If they are, then the chances the heater core is plugged becomes more likely.

I would also check that there is no air bubbles in the system. There is a bleeder screw on top of the engine that will bleed the air out of the system.

Here is the complete bleeding procedure:

1. Turn ignition switch On and set front temperature control knob to full warm position. On vehicles with rear heater, ensure rear blower switch is in any position except OFF.
2. Loosen engine air relief plug, Figure 1, then radiator air relief plug, Figure 2, three turns. Do not remove radiator air relief plug.
3. Remove air duct, then loosen heater pipe air relief clamp and remove cap, Figure 3.
4. Install a hose to heater pipe air relief tube, then add a 50/50 mixture of coolant and water to MAX mark on coolant reservoir.
5. Install other end of hose in coolant reservoir. Ensure hose end is submerged in coolant at all times.
6. Place a drain pan under radiator relief plug opening, then slowly pour a 50/50 mixture of coolant into radiator, allowing several minutes for air to escape.
7. Fill radiator with coolant until coolant starts to drip from radiator air relief plug opening, then close plug, tightening to specifications.
8. Pour more coolant into radiator while gently moving upper radiator hose up and down.
9. Install a wire under radiator pressure cap negative pressure valve, Figure 4, to allow flow of air and coolant regardless of pressure. Do not install cap at this time.
10. With engine air relief plug open, radiator filler cap off, and selector lever in P position, start and run engine at 2000 RPM until lower radiator hose becomes hot, indicating thermostat has opened. If coolant comes out of engine air relief plug, close it. If coolant level in radiator filler neck lowers, add coolant. If coolant overflows from radiator filler neck, install radiator pressure cap (with wire installed).
11. Close engine air relief plug if it is not already closed, then stop engine and allow to cool down completely.
12. Refill radiator and coolant reservoir as necessary, then install radiator pressure cap (with wire installed) and again warm engine to normal operating temperature.
13. Observe temperature gauge closely. If gauge begins to rise above normal, stop engine and allow to cool down completely, then refill radiator and coolant reservoir as necessary.
14. On models without rear heater, run engine at 3,000 RPM with temperature control knob in full warm position for five minutes or until outlet air is hot. Keep coolant reservoir at MAX level. Repeat procedure three times to ensure no air is trapped in system.
15. On models with rear heater, proceed as follows:
    • Run engine at 3000 RPM with front temperature control knob in full cool position, and front and rear blower switches in any position but Off, for five minutes or until rear outlet air is hot.
    • Repeat procedure three times to ensure no air is trapped in system.
    • Turn rear blower switch to Off position, front temperature control knob to full warm position until front outlet air is hot.
16. Stop engine, then pour coolant mixture into coolant reservoir to MAX level.
17. Allow engine to cool down, then remove radiator pressure cap.
18. Remove wire and reinstall radiator pressure cap, then remove hose from heater pipe air relief tube and quickly reinstall cap and clamp.
19. Install air duct.

Another thing that I have found to be helpful when refilling a Nissan V-6 is to raise the front of the vehicle about one or two feet to help the coolant flow into the cooling system.

Additional Information provided courtesy of ALLDATA