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

 

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?

 

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.

 

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

 

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

 

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.

 

Ah, I didn't know the diesels had a separate vacuum pump for that. Unless the vent temp was hot too, I probably wouldn't go the vacuum route then. Does your truck have headers? If you were towing, it may have just been getting really hot. Just a thought. Sorry I couldn't be more help.

Well, I suppose it would depend on when it does it. At high throttle settings, or all the time? If all the time, do other vacuum controlled things still work? If not, the first thing I would probably do is check engine vacuum with a gauge and also check the main vacuum line from the upper intake to the blower housing area. Just a start. You might see a problem visually, but I would want a vacuum handpump myself. There may also be a problem with the selector valve that's part of the control panel. Here's a diagram for a 91. Yours may have some differences.

Chris