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my car is a 1995 Jeep grand cherokee 5.2L, I have heat less than 20% of the time changed water pump and thermostac last october.,both heater core hoses are very hot the upper radiator hose is hot and the lower radiator hose is cool why don't I have continues heat? Please help

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Cooling system problems suck to diagnose because you can't see inside.

No heat can be caused by three things no heat, no flow, other.

The no heat part is easy. If the engine is not hot then you have no heat. This does not seem to be your problem.

No flow is much more difficult. Anything that restricts flow in the heater core will kill the heat. This includes but not limited to a plugged up heater core, an air bubble in the heater core or the impeller worn off the water pump. Since the water pump is newish then the other two might be a problem. Try squeezing the heater hose while the engine is running as see if you can feel flow in the hose. This may be difficult to do and is often subjective. Flushing the heater core is a better bet. Garden hose in one side and see what come out the other side. Flip back and forth from one side to the other side to dislodge anything in both directions.

Other gets more complicated. Jeep Grand Cherokees are known to have problems with blend doors. The blend door is the part inside the dashboard that moves back and forth to change the temperature coming out the vents. The plastic gets brittle and the door snaps, usually around the part that turns it. The problem gets even worse if you have dual zone climate control. When you have heat see if changing the temperature does anything. If it doesn't then remove the motor that's responsible for the blend door and see if the door is cracked or broken. The repair involves removing the dash, removing the HVAC plenum and replacing the blend door. It may involve discharging the AC for disassembly. It's a sucky repair.

  • I remember heater jobs : workshop manual gave 8.5hours for the job - able to do it in 4.5 so good for the bonus!! – Solar Mike Feb 3 '18 at 9:09
  • @SolarMike - The joys of book hours, especially if you know good solid shortcuts. Nothing like getting paid for 60 hours work when it only took you 40 ;-) – Pᴀᴜʟsᴛᴇʀ2 Feb 3 '18 at 13:25
  • I'd suggest your blend door observation is probably the culprit here, considering both heater hoses are hot according to the OP's description. Whether it's the door itself or an actuator would be hard to diagnose on this side of the internet. – Pᴀᴜʟsᴛᴇʀ2 Feb 3 '18 at 13:28
  • @Pᴀᴜʟsᴛᴇʀ2 My all-time favorite book hours were the lateral links on a Mazda Millenia. They paid over 11 hours. You could usually slide the bolts out without dropping the cradle. If you couldn't then making a small dent in the rail did the trick. Cut it down to 45min, an hour if something was frozen. – vini_i Feb 3 '18 at 13:34

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