Cold running truck

C

Chihuahua Floyd

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Picked up an older F150 a couple of weeks ago. 1999, 4.2L V6, 5 speed. No heat, so off it goes to my local guy. New thermostat, but truck still won't get warm. Let it sit at garage and idle for 45 minutes, still won't get warm. Infrared thermometer reads 120 on housing for thermostat.
All I can think of is the new thermostat is bad also?
CF
 
Chihuahua Floyd said:
Picked up an older F150 a couple of weeks ago. 1999, 4.2L V6, 5 speed. No heat, so off it goes to my local guy. New thermostat, but truck still won't get warm. Let it sit at garage and idle for 45 minutes, still won't get warm. Infrared thermometer reads 120 on housing for thermostat.
All I can think of is the new thermostat is bad also?
CF
Click to expand...
Check that the blend door is function as it should?

Have you flushed the heater core? My old inline 6 f150 didnt have heat, due to the core being clogged up with rusty gunky. Very easy to flush in the driveway with a water hose.

Make sure there isnt any air in the system that has gathered in the core, which will stop any hot air from coming out of the vents.
 
jmccracken1214 said:
Check that the blend door is function as it should?

Have you flushed the heater core? My old inline 6 f150 didnt have heat, due to the core being clogged up with rusty gunky. Very easy to flush in the driveway with a water hose.

Make sure there isnt any air in the system that has gathered in the core, which will stop any hot air from coming out of the vents.
Click to expand...

I had never, ever heard of a blend door, and now I've heard it twice in a week. Lol.
 
kcult said:
I had never, ever heard of a blend door, and now I've heard it twice in a week. Lol.
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They're not fun to replace. Usually taking out the entire dash/steering wheel most times.
I had to do mine on the mercury, cheapest shop was like $700... I took the passenger air bag out and got my arm back behind the radio and worked blind to get it replaced, because I wasnt paying 700 for that crap lol
 
Another heater core fail on a ford. Lucky if it is you should be able to do it without much trouble.

Sent from my SM-G965U using Tapatalk
 
Heater core has circulation, first thing Greg checked. Top radiator hose gets warm, but not hot. I'll look into blend door after Christmas.
Thanks.
CF
 
Not the top radiator hose... the heater hoses.

On my Dodge Dakota, I have a valve to turn off the heater core flow when I want to use A/C. That's a solution for the blend door that won't close all the way.


Wait a minute... are you saying that the engine runs cold, as well as the heater being inop?
 
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Is the top radiator hose also about 120ºF. If so that would prove that thermostat was open and coolant is circulating.
 
Engineers runs cold, so no defrost or heat in passenger compartment. Hoses to heater core, one is warm, one is cold. Engineers just does not warn past about 120 or so.
CF
 
Chihuahua Floyd said:
Engineers runs cold, so no defrost or heat in passenger compartment. Hoses to heater core, one is warm, one is cold. Engineers just does not warn past about 120 or so.
CF
Click to expand...

In my experience, its one of two things.

Thermostat is stuck open. (If already replaced and feel like its fine, more likely the next thing)
Low on coolant/air in the cooling system.

I KNOW one of my vehicles would not put out any heat....merely due to about a qt TOO low on coolant.
 
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Chihuahua Floyd said:
Engineers runs cold, so no defrost or heat in passenger compartment.
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Assuming auto-correct... engine runs cold, so no defrost or heat. Is there a temperature gauge? If so, does it show the engine not reaching operating temperature?

Chihuahua Floyd said:
Hoses to heater core, one is warm, one is cold.
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Refer to post #4 above... plugged heater core. That would explain both the lack of defrost and the lack of heat in passenger compartment.

Chihuahua Floyd said:
Engineers just does not warn past about 120 or so.
CF
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I don't know what this means...
 
120 degrees measured by a hand held device? and not with a scan tool to see actual temp?.

Focus on the heater core first. Disconnect the hoses, use a spare peice of heater hose and the garden hose, flush, run water for abit in both directions. Reconnect, top of coolant system and retest after holding the throttle at about 2500 rpm for at least 3 minutes. See what you have now
 
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MacEntyre said:
Interesting... I would have thought you would focus on making sure the engine is operating in the right temp range, then look at the heater.
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Without real time data via a scan tool, no way for sure to tell if the engine temp is not up to operating temp.

plus, "120 degrees" in and out of heater core would give some heat through the cabin vents
 
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Related question. I drove my 78 Ranchero to work the other night and it didn't get warm either. A while back I was driving and it the engine got really hot when I was sitting in a drive through. Would a clogged heater core explain that as well?
 
J R Green said:
Related question. I drove my 78 Ranchero to work the other night and it didn't get warm either. A while back I was driving and it the engine got really hot when I was sitting in a drive through. Would a clogged heater core explain that as well?
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No to your question. Probably low coolant level
 
Ammoholic said:
In my experience, its one of two things.

Thermostat is stuck open. (If already replaced and feel like its fine, more likely the next thing)
Low on coolant/air in the cooling system.

I KNOW one of my vehicles would not put out any heat....merely due to about a qt TOO low on coolant.
Click to expand...

I had that experience once as well. Seemed too simple to diagnose at the time.

.
 
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