This is my first post here. I've always had good luck searching for and finding a fix for my truck problems. This time though...not so much. Here's my issue...

I have an 07 F150 4.6L. I noticed the heat was only luke warm at best, and would fluctuate between cold, luke-warm, and very rarely warm. I changed the thermostat and in the process broke the corroded by-pass tube. Replaced by-pass tube and water pump, which cracked when removing the tube. Can you sense my frustration here? So in review; I have a new water pump, thermostat, by-pass tube, and fresh anti-freeze. However, I didn't flush the system. Started and drove the truck for a few days...same heat issue. Next I checked the feel of the heater core hoses. In flow was hot, out flow was luke warm...a noticeable difference. So i blew out the heater core with compressed air. All kinds of debris came out and I felt fairly confident that was the problem. The heat blew hot for about the first 5 mins. Then the same problem. I've read about the blend door being a possibility, but I don't see, or hear, any of the symptoms of one being bad. I'm not a mechanic, but I am mechanically inclined and usually do my own repairs (maybe that's the issue). Any thoughts or suggestions from the gurus out there. I hate to break down and take it to a shop for repairs...

Thanks,
Mike

 

"I noticed the heat was only luke warm at best, and would fluctuate between cold, luke-warm, and very rarely warm".....
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-this is a common symptom of a blend door problem. the air goes thru the heater core and gets hot. some of the air goes around and is then MIXED ( hot and cold) to get the temp you select on the dash. If the temp of the air swings, it is possible that the blower motor is pushing the damper door around and not constant..Blend door is motor operated and is under the radio against the duct work. On the older trucks you can see the motor from drivers floor looking up... 07 MIGHT be the same. REmove plastic around / under the radio and inspect.. motor turns a gear box / cam / shaft / that connects to damper door.

 

see drawing below of air flow thru the duct.

https://www.ford-trucks.com/forums/9...-please-2.html

 

Thanks for your response Steve. I NOW HAVE HEAT! I'm thinking I had air in the system and didn't purge well enough. I would get fairly warm air with the engine running at speed. When I came to a stop light and engine idle, cool air. I took it out on the expressway and ran a constant 65mph for about 1/2 hour. Blasting HOT air now. As hot as I can ever remember it being. Off the expressway and in stop and go traffic, heat stayed constant...HOT. I let it idle in the driveway for about 15 mins and the air stayed HOT! Tomorrow morning will tell the story...morning temp in the low 20's. We'll see how it warms up...normally takes only a couple mins to get the heat going.
Thanks again for your input.

 

YEP....... coolant level is the FIRST thing to check...I just assumed it had been done.. good find !

 

I've never had to deal with air in the system like what happened here. Usually I refill, wait for the t-stat to open, top off, and away we go. I did that this time too. I think the third time was the charm. This whole thing started with changing out the t-stat. I think maybe ill stick to being a carpenter...and take it to the pro next time.

 

In case you have to do it again, you get it as full as you can and drive the truck enough to warm it up all the way. Then you let it sit until stone cold (at least 2 hrs in the winter). Look at the level in the surge tank and add coolant as needed. It might take half a dozen cycles to get all the air out.
As a maintenance/check item, look at the surge tank once a month on a hot engine and note the level, then the next morning when it's cold look at it again to see that it is lower - should be maintained at the 'low' level when cold. This proves that the system is airtight; the hot coolant expands and the level in the tank rises. The cold coolant contracts and the vacuum draws it back into the engine. Probably only 1 in 100 even understand what I just said or why it's important. If you run that check and the level doesn't change, there is a leak in the system.

 

If you can park it facing uphill on as steep a grade as you can, it tends to help purge the air out during that cool-down cycle.