Preparing for winter trips, I reconnected the front and rear heater hoses (long story). It used to run with the temp gauge smack in the middle of the range. Now it runs 1/4 (towards the cold side) without heat and 3/4 (towards the hot side) with heat and there isn't much heat from the vents. I flushed the cores so I don't think they're clogged. What the heck is going on? Could air in the lines cause this?

Is there a coolant valve at each core - I don't see anything under the hood - or do they run hot all the time with a flap to direct cabin air around them when cooling?

Sixto
93 E150 Chateau 5.8 192K miles

 

no body else has replied yet, so thought I would reply.. I am not familiar with the 4th gen e150's.. I do own 2, 3 gen e150's though.

First might be air in the system if everything was disconnected..
Second, have you checked the water level after running it a while.. the air will eventually work its way through the system. As it does the water level will drop in the radiator. When you turn the heaters on (with air in the system) they may use some of the water lowering the water level in the radiator...

I have never experienced this but have heard that with some systems, (i don't know about yours) if the radiator is partially clogged, that instead of all the water flowing through the radiator to cool it down, flow will increase to the heater cores and decrease to the flow to the radiator. True the heater cores are like small radiators but do not have the cooling capacity of the radiator.

Another thing could be something in the electrical system due to draw from the fans running. My 88 150 gauge swings quite a bit from 1/4 the way up to almost hot. But when I checked it with a digital thermometer, the water temp was only varying 7 degrees. I haven't done it yet but assume my problem is the temp sender unit.. If not then it is perhaps the gauge or instrument cluster voltage regulator..

Double check for water level, bleed the system. I went to AZ and used their digital thermometer while in their parking lot (they didn't have a loaner). Check the temp right at the thermostat housing and intake manifold.. Check it when the gauge is reading low and record the temp. Turn the heaters on and let it heat up then check the temp again..
Hope some of this might help.

 

Must have been trapped air. I drove it some more, pressure tested at the radiator and the cap, I didn't have to fill the reservoir because it was full, now the gauge stays fixed at 1/4 (to the cold side) with the cabin temp selector on full cold, full hot or in between.

Sixto
93 E150 Chateau 5.8 192K miles

 

Good news.

Fords seem to corner the market on air trapped in the cooling system. And driving them seems to be the only way to get the air out. I have tried running the engine in the shop with the cap removed and that never seems to get all the air out. Once they "burp", everything works great.
jim