I own a 2003 5.4L Eddie Bauer Expedition (123,000 miles) with front and rear heat and A/C.

Okay, so here's the issue I have. When the truck is running, the front heater kicks out some decent heat, the rear heater is luke warm at best. When in drive and waiting at a light, both front and rear heaters blow cold. When driving down the street and keeping the rpm's up above 2,000, it blows hot again.

This is what I've done to try and fix this. I've flushed the antifreeze out by opening the petcock on the radiator, removing the allen head drain plug on the engine block and blowing water through the reservoir tank and the upper heater hose coming off the front of the engine block until all coolant was out and running clear. I then used an antifreeze flush from Prestone and ran that (without the thermostat) for 15 minutes and repeated the flush as described above. I replaced the water pump and thermostat (My thinking was that I wasn't getting the circulation needed so I replaced the water pump), then put 20 quarts of new antifreeze and water with a 50/50 mix.

The engine temp gauge goes slightly more than halfway up, so I know the engine is heating correctly. The unusual thing is that this affects both the front and rear heater cores simultaneously. It would be highly coincidental that both heater cores are bad at the same time. I'm wondering if this could be something in the heater hoses that is going bad, a restrictor valve, or coolant diverter valve, etc.

Any help/advice would be appreciated. This is my wife's ride, so like Big Ben, I gotta hear about it every hour on the hour.

Thanks in advance guys!

 

You problem is as you suspected, not enough coolant being circulation through cores. There are a couple of reasons this could be happening. Like, a bad diverter/shut off valve (not opening all the way), some other form of restriction like clogged heater cores (or hoses), or the system could just be air bound.

 

I'm still doubting it's both heater cores. So I've ordered the replacement heater hose assembly that includes the flow restrictor and vaccuum operated coolant shut off. We'll see if either of those are the problem I guess.

 

While I haven't tested it yet, I think it's a blown head gasket. The coolant system continually over pressurizes injecting air into the system. The antifreeze then blows out of the Degas bottle while driving. The air in system causes the heater core to blow cold. I'm going to test tomorrow for hydro-carbons present in the Degas bottle. If it is, blown head gasket.

 

Read this, it may apply to your problem. If it helps let us know.

SECTION 303-03: Engine Cooling 2000 Expedition/Navigator Workshop Manual

GENERAL PROCEDURES

--------------------------------------------------------------------------------

Cooling System Draining, Filling and Bleeding
Draining

WARNING: Never remove the pressure relief cap while the engine is operating or when the cooling system is hot. Failure to follow these instructions can result in damage to the cooling system or engine. To avoid having scalding hot coolant or steam blow out of the degas bottle when removing the pressure relief cap, wait until the engine has cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly. Step back while the pressure is released from the cooling system. When you are sure all the pressure has been released, (still with a cloth) turn and remove the pressure relief cap. Failure to follow these instructions may result in personal injury.

CAUTION: The coolant must be recovered in a suitable, clean container for reuse. If the coolant is contaminated it must be recycled or disposed of correctly.

NOTE: About 80% of coolant capacity can be recovered with the engine in the vehicle. Dirty, rusty or contaminated coolant requires replacement.

Release the pressure in the cooling system by slowly turning the pressure relief cap one half turn counterclockwise. When the pressure is released, remove the pressure relief cap.
Place a suitable container below the radiator draincock (8115). If equipped, disconnect the coolant return hose at the oil cooler.
Open the radiator draincock.
Close the radiator draincock when finished.
Filling

Add the correct engine coolant mixture to the degas bottle.
Move the temperature blend selector to the full warm position.
Run the engine until it reaches operating temperature.
Add the correct engine coolant mixture to the degas bottle until the coolant level is between the "COOLANT FILL LEVEL" marks.
Turn off the engine and allow the cooling system to cool.
Repeat Steps 1 through 5 until the degas bottle level is OK.
Bleeding

Select maximum heater temperature and blower motor speed settings. Position control to discharge air at A/C vents in the instrument panel (04320).
Start engine and allow to idle. While engine is idling, feel for hot air at A/C vents.
CAUTION: If the air discharge remains cool and the engine coolant temperature gauge does not move, the engine coolant level is low in the engine and must be filled. Stop the engine, allow to cool and fill the cooling system as described.

Start the engine and allow to idle until normal operating temperature is reached. Hot air should discharge from the A/C vents. The engine coolant temperature gauge should maintain a stabilized reading in the middle of the NORMAL range and the upper radiator hose (8260) should feel hot to the touch.
Shut the engine off and allow it to cool.
Check the engine for coolant leaks.
Check the engine coolant level in the degas bottle and fill as necessary. For additional information, refer to Cooling System Draining, Filling and Bleeding in this section.

 

Thanks Moto Mel. Been there done that. Flushed the system exactly as described.

I'm really thinking it's a blown head gasket. I've heard of oil leaking on the rear passenger side of the engine is another sign, and I have that too. I'll know more tomorrow.

 

Yep the head gasket was blown on the #1 and #4 cylinders. Right above each cylinder is two holes for coolant to flow. The leak was occuring here. Combustion was entering the cooling system, over pressurizing it, introducing air into the system (thus the heater sometimes blowing hot than cold) and blowing antifreeze out the cap at the Degas Bottle. When the engine sat, coolant would leak into the cylinder so when it was first started would run like crap and hesitate until all burned off. Below are some pics.

Below is a picture of the #1 and #2 cylinders. Notice how much cleaner the #1 piston is than the others.
http://i965.photobucket.com/albums/a...4/DSC02908.jpg

Below is a picture of the head gasket. The #1 cylinder is on the left. You can see how much cleaner the gasket is (12 o'clock) at the top than the #2 cylinder is on the right. Again, this is where the antifreeze was leaking. The two small holes at 11 o'clock and 1 o'clock is where the coolant jackets are.
http://i965.photobucket.com/albums/a...4/DSC02907.jpg

Finally, this last picture is of the cylinder head. #1 is on the right. Again, it's noticably cleaner between the two cooling jackets than on the #2 cylinder. The #1 dome is obviously cleaner than #2 as well.
http://i965.photobucket.com/albums/a...4/DSC02906.jpg

This all started because my truck had intermittent heat issues, blow hot than cold, than hot again, etc. Hope this information helps others!

 

Glad you are getting it repaired and that you diagnosed the problem correctly. It's too bad that it's such a PIA job, but at least you'll have your truck back on the road soon.
I imagine you really could use it right about as it looks like most of the country will be getting an arctic blast this weekend.
Let us know if it all works out.

 

I'm noticing the oil burning issue in the other cylinders. Those cylinders should not look that black at only 123K miles. Are you running regular oil or synthetic?

 

Always ran Mobil 1 synthetic. Never had an issue with oil burning and never had to add oil between oil changes.

 

Hmm, maybe it just looks worse in the picture than it actually is.

 

It could have been running overly rich.