Excessive heat bleed?
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Cargo Master
Joined: Oct 2010
Posts: 2,339
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From: Lost In a Pit of Despair
Excessive heat bleed?
So yesterday and today I've been towing a couple cars around with my 87 F250 with a 6.9 in it. Yesterdays load was small, a VW baja for about 100 miles on the freeway. Today, I was pulling a 80's chevy short wide truck, for 8 miles up and down hills. Both were on a 2200# trailer.
Now the temp needle never got higher than normal with either trip. But I noticed that down under the dash, it felt like the heat was blasting on high even though it was set to cold and blowing on my face.
So I guess, is it normal to have a lot of heat bleeding through the firewall? I don't know if it has any correlation with the towing, because I've never noticed it before.
Thanks
Jameson
Now the temp needle never got higher than normal with either trip. But I noticed that down under the dash, it felt like the heat was blasting on high even though it was set to cold and blowing on my face.
So I guess, is it normal to have a lot of heat bleeding through the firewall? I don't know if it has any correlation with the towing, because I've never noticed it before.
Thanks
Jameson
Junior User
Joined: Apr 2013
Posts: 61
Likes: 0
I know you've got an older truck but I was reading the manual for our explorer today and read that the heat automatically kicks on while towing to help cool the engine. The explorers an 03 and I have no idea how it would know you're towing or even if your truck does that but something to consider right?
Postmaster
Joined: Mar 2013
Posts: 3,066
Likes: 7
From: Over There
Hard to say, there isn't anything different the truck does while towing. Only thing I could imagine is that the radiator fan finally had to move a fair amount of hot air and if you were turning more RPM then you were pumping more hot water through the heater core and you were feeling the effects of that. These trucks don't have a valve that shuts off the hot water to the heater core when set to cold.
Senior User
Joined: Aug 2001
Posts: 275
Likes: 1
From: Lexington Park, MD
Did the air blowing out the vents get warm also? High throttle can reduce the vacuum enough so system's vacuum motors let go and the airflow changes directions. I've heard of this happening to guys when towing.
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
Thread Starter
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Cargo Master
Joined: Oct 2010
Posts: 2,339
Likes: 32
From: Lost In a Pit of Despair
Did the air blowing out the vents get warm also? High throttle can reduce the vacuum enough so system's vacuum motors let go and the airflow changes directions. I've heard of this happening to guys when towing.
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
Didn't quite feel like it was blowing. It was hard to tell because the fan was on high, and I had my window open. But it felt like it was blowing at a really low speed, similar to the very slow speed the fan blows even when I have it set to off.
-Jameson
Junior User
Joined: Apr 2013
Posts: 61
Likes: 0
Did the air blowing out the vents get warm also? High throttle can reduce the vacuum enough so system's vacuum motors let go and the airflow changes directions. I've heard of this happening to guys when towing.
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
In my 91, if you lose all vacuum to the motors, it will default to DEFROST, but a partial vacuum will send some air to the floor. This of course, doesn't explain it if the vent air didn't also get hot, because the temperature blend door is cable controlled, not vacuum controlled. Did you feel air blowing out the floor duct, or was it just hot down there?
Chris
Senior User
Joined: Aug 2001
Posts: 275
Likes: 1
From: Lexington Park, MD
The air blowing through the vents was only cool, about the same temperature as the outside air. A/c needs a charge, so it wasn't blowing cold. Diesels have a vacuum pump, so there is minimal change of vacuum.
Didn't quite feel like it was blowing. It was hard to tell because the fan was on high, and I had my window open. But it felt like it was blowing at a really low speed, similar to the very slow speed the fan blows even when I have it set to off.
-Jameson
Didn't quite feel like it was blowing. It was hard to tell because the fan was on high, and I had my window open. But it felt like it was blowing at a really low speed, similar to the very slow speed the fan blows even when I have it set to off.
-Jameson
That would explain why when I turn on my heat/ac I an only get it to come out of the defroster. Ny tips on how I should attack this? Sorry for hijacking the thread jgavac.
Chris
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