I have a 2000 expedition with about 120,000. Recently started having some weird heater issue but could not find a clear post on here that had the same issue.
When driving down the road the heater blows fine and very hot. When stopped at a light the heater will still blow but the air will go cold. I don't think it is the core but I could be wrong. The heater hose gets hot and stays hot. Heat in the rear is hot as it should be. Thanks for any help.
If the coolant level is fine and within proper range, then there are a couple possible causes.
First, the coolant pump is on its way out. Not always will a failing coolant pump leak through the weep hole. Some pumps use internal steel components. If the coolant isn't changed/flushed regularly the impeller fins inside the coolant pump can slowly corrode causing less, and less flow over time. Once you increase engine RPM (increase in speed), would explain why you get heat.
Second thing, is if you have a rear heater unit, this unit is run by a booster, or aux. pump. If you keep the rear heat off this shouldn't be an issue for the front heat, but to rule out a coolant pump issue you can try running the rear heat if your vehicle is equipped.
The blend door effectively closes/opens too allow heat to enter the cabin. The 'cool' setting on the dash control knob over rides the heater core. If your coolant level is down (nothing in the reservoir) this can mean that there is one or more air pockets in the system. Now, this can also be the cause of lack of coolant reaching the pump to effectively circulate the coolant through the heater core. Should there be an air pocket, refill the coolant reservoir, drive the vehicle and check and refill as necessary to work out all the air.
The heater core may also be partially blocked inside with rust/debris. A back flush of the core generally helps alleviate any future problems. There are garden hose kits for this, but be cautious as engine coolant will come out when you remove the hoses from the core that enter in through the firewall.
If uncertain contact a local shop and they can perform a coolant pressure test, which can help diagnose a bad/faulty pump, or a block in the system.
Hello, I'm new to this forum, but not new to my truck. I have the same problem but can't get enough proper information. I have a 98 EB 5.4 with front/rear climate control. I've just changed the thermostat, used the flush kits that you install on the heater hose. Seems like there are 2 heater hoses? I've read there are 2 heater cores, where is the rear core. When I'm sitting and revving the engine I get good heat, when I'm driving, the RPM's change and I get some heat, now this is from both systems, front/rear. The truck has 250K on it. The water pump has never been changed and the truck did sit for about 3 yrs not started. To its credit, I put a battery in it, and it started right up, (Ford Tough!). Now, I'm thinking that the problem would be the water pump, the truck does not over heat or run hot at all. There seems to be a mention of an aux pump for the rear heat, does anyone know if this is true, if so where is it located? because the heat does get hot when I sit and rev it, it leads me to believe that it's the water pump, keep in mind that this happens with the rear heat as well. Anyone have any ideas? Replacing the water pump is a lot easier than the heater core, or the door...
Last edited by gumbedamit; 10-23-2012 at 11:27.
Reason: Additional Info
I replaced the thermostat, not much heat.
I cut the hoses in the back to flush the heater core. There was a little bit of sediment.
I got some heat, but I also noticed that with the truck running, there wasn't a great deal of pressure getting to the back core; this would lead me to believe it was a waterpump issue. After driving for awhile I would get heat, but it was still ice cold in the front. I cut both hoses in the front where it goes straight into the heater core, that way, there would be one way in, and one way out. There was a blockage there.
Connected the hoses and got heat in the front and the back. I still need to change the waterpump because it takes a long time to get that heat because of the low volume of flow. I knew that my blend door was in good order because I could hear it opening/closing. I will let you guys know next week what happened with the waterpump. If you guys have blocked cores, try connecting a hose to the hoses coming directly in front of the core, turn the water on slowly as to NOT BLOW YOUR CORE>>>>
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