2nd Gen Non-Engine/Transmission no heat

[SeanM]

my truck has very poor heat and i cant figure out why. I know its not the blend door actuator and I dont think that its the heater core as both heater hoses are around the same temp as the upper radiator hose. My thermostat is also function properly. The only other thing I can think of is the blend door gaskets but I am pretty sure they are sealing good as I can feel the door suck close when I turn the blend door manually. I am at a loss and plan on removing the hvac housing this coming weekend. While I am in there I plan on replacing the heater core, blower motor, and blend door actuator. I was just wondering if anyone had an idea on what could be causing my poor heat situation.

 

[Seane1987]

How is the air flow out of the vents? you don't get any heat with the door turned manually?

 

[SeanM]

air flow from the vents is normal and yes i get some heat but not much. If it is less then 30 degrees outside my truck is barley warm. if its below 20 degrees its a freaking ice box.

 

[Joe Mc]

I have same issue, 2nd winter, I'm going after the heater core and A/C evap this spring.



Lat winter I locked the blend door closed = removed vacuum line and wire tied the door closed - didn't help.



I'm guessing when I remove the coils there's going to be a TON of debris on the inlet side of both. The other day I had the heat on the hi vents, fan speed hi and a pine needle flew out and stuck in my eyeball . . . #@$%! Just kidding about sticking in my eye but a pine needle did fly out the center vent



Probably should go for the cowl filter kit from Geno's after I get new coils . . .

 

[SeanM]

ok, new question. What kind of foam have you guys used to reseal the different doors in the hvac housing?

 

[mwilson]

Have you flushed the heater core????



Remember if the hoses are the same temp as the upper radiator hose is doesn't mean much as the thermostat hardly if ever opens in real cold weather.



My son and I have been half frozen running the '97 this week. Was -11 below Monday morning and -8 below this morning.



Found two things wrong...



(1) Truck had straight antifreeze. That is a no-no as it will not flow thru the core when cold. Could hear it when I started the truck, wicked racket as it tried to get thru the core.



(2) Flushed the heater core and drained some antifreeze out so as to add water before leaving work tonight. Not much sludge showed up but what a difference now!!! Simple to do, just slid the hoses off of the steel pipes at the rear of the engine and used the washbay water hose.



Both mornings I had the fan on high and temp all the way up and it just barely was 40 or 50 in the cab.



Tonight after our quickie repair we had to turn the fan way down and the temp knob almost to center as our feet were cooking!!!! Only 18 degrees here right now.





Check those two items before you tear the truck apart, might be worth doing.



Mike.

 

[SRath]

Yup. There's a reason you should keep your coolant/antifreeze mix between 50% and 60%. Coolant also does a very poor job of transfering heat compared to water, so it will neither cool your engine or heat your heater core as well as a proper mix.

 

[The patriot]

I flush my cooling system every year, replaced the ac evap and heater core and my truck still isnt as hot as you'd expect.

I did 50/50 on the af.

I'm not the type of person who likes the heat, and it's not even close to making me "hot" at temps below +10 F.

I run a cover over about 80% of the radiator in the cold weather. It helps a little.

 

[SRath]

My buddy had a Ford gasser like that. No heat even with ALL new cooling system. I have often wondered if it is possible for an air bubble to remain in a heater core. I just flushed and changed the coolant on an old Chevy. When filled with water and flush chemicals, and before I did all the cooling system work, it would cook you out of the cab in minutes!



But when I refilled the system (and I also drained the block after flushing), I had a HECKUVA time getting the air all out of the block and, more likely, the higher-positioned heater core! Even after I used the heater hose inlet to refill the block, I still had to change the angle my truck was parked at in my driveway (just a slight slope & tilt) AND pump the upper hose like a squeeze ball and loosen some hose clamps for air bleeds to get the air out and get coolant flowing enough to get any heat out of the heater. It works great again now, but I nearly froze and wasted a lot of coolant mix getting the air out. The engine compartment really needed a bath afterwards.



Is it possible that trucks with chronic "no heat for no good reason" problems have a super-stubborn air bubble trapped in the heater core? If there is any air remaining in the system, it only makes sense that it would be in the heater core, which sits highest.



Heater cores are tiny, so it wouldn't take much air to keep any significant heat transfer from occuring. It would also shorten the core's life by not providing the corrosion protection that contact with a good coolant would.

 

[mwilson]

I don't think the Dodge heater cores are sensitive to that. That Cummins is shoving water thru the core at a pretty good clip and I am pretty sure that the bleed valve (the one with the short 90 degree rubber hose hooked to it) on the thermostat housing will take care of any air all by itself.



I have owned vehicles that would get air-bound but the heater core was always quite a bit higher up than the rest of the cooling system (such as Honda Accords, Oldsmobile Cutlass Supremes, etc. ) and all had a place to bleed them while filling the cooling system to prevent air lock.



I can not believe the difference in the cab heat after the simple, quickie flush that we did. Granted, the previous owners straight antifreeze treatment did not help it any, but the flush is what really brought the heat back.



There is also the option of fan removal for winter time use, removed the fan and clutch every winter on my old '94 and the '98 that I had.

You just have to remove the A/C clutch relay at the same time so that the system doesn't come on while in defrost. Also have to watch the transmission temp as that will heat up sitting at a traffic light way faster than the engine will at an outside air temp of 30 degrees for example.

 

[SRath]

Air doesn't willingly flow downwards in a liquid system. It fights it hard, in fact. Even with a new high-flow pump. Even with all the bleeds you care to add down below. Most times, yes, it gets bled out. I have changed and flushed coolant many times on these old chevys over the years, seldom with any problem at all. But this time it was different. It was a real fight.



So, if not trapped air, and if everything else is new and perfect and identical, how do you explain two identical trucks having such a huge difference in heat output? An air bubble is the only thing that makes sense to me.



Maybe the problem will go away with the installation of a new heater core. But that might not be because the old one had anything wrong with it. It might just mean the new one did not trap any air this time.

 

[mwilson]

It could well be the issue, just have never seen it with any of my Dodges. I have owned 4 2nd gens and 1 3rd gen, all with Cummins power and have never taken any precautions regarding air when tinkering with the cooling systems.



The 5. 9 is also used in cranes and other equipment where the cab heater is higher than the engine/radiator and there are no heating or air issues, believe me I would hear about it if there were any cold crane operators.



I am pretty sure the top of the core is no higher than the upper radiator hose in the Dodge's but will look again tonight.



I have been around vehicles long enough to know that there exceptions with them all and can not say it can't be air, all I will say is it shouldn't be air. :-laf



Correct Thermostats are very important for these Cummins motors and wonder if an aftermarket one gets installed if the performance is as good. Maybe until the truck is operated in extreme cold??????:



I do think he should at least attempt a flush before ripping the HVAC unit out if he hasn't done so already. Might free up his weekend:-laf



Mike.

 

[SRath]

I wasn't referring to just dodges or cummins. I have seen and heard of this phenomenon on many vehicles over the years. Seen folks replace everything in a cooling system -- twice -- and still get no decent heat output. Every range of thermostat.



I can't believe air would get stubbornly trapped that long or more than once, either, but it sure does baffle me how one truck can toast yer toes and another identical one tost yer fresticles...

 

[mwilson]

It might be a good policy to fill the heater core with coolant while on the bench on its back before installing it into the HVAC box if the ends could be capped tightly while installing.



No reason that could not be done, and lessen the odds of a big fat air bubble lurking in there somewhere.



Just thinking... .....

 

[SeanM]

Well any thing is worth a shot. I reversed flushed the cooling system last summer and replaced the radiator. I have the machine for doing coolant flushes at work so I know it was flushed right and that it has has the proper mix. I haven't how ever just flushed the heater core. I will try that after work and see if it helps.

 

[KKlingbeil]

I have played with the heating issue in 2nd Gen Dodges as well. I replaced the heater core, and have a 50/50 mix of antifreeze. My conclusion is that when the air is really cold, the heater core itself does not have enough surface area to properly heat the cold air. I used a thermocoupler in the foot vent and found that if you turn the fan from high to the next click down it makes the outcoming air much warmer. I dont recall all the actual numbers. I believe the warmest air I could produce with a fully warm engine running down the road with front end 90% blocked was around 75degrees. Outside air temp around zero.



The area of the heater core IMO is too small, and when the fan is on high, the air velocity is to fast to properly heat the air. Thus when you turn the fan down, lowering the velocity, the air becomes warmer, but with less flow. My end solution was that it is what it is. I generally run with the fan on 3 instead of 4 (high). These were my findings... . hopefully someone else has a better answer!

 

[mwilson]

Let me know if the flush helps, I can't carry on enough about the difference that just made for mine.



First morning this week that I have showed up at work not shivering like a dog pooping razor blades... ... ... ... . :-laf:-laf

 

[mwilson]

I have my point and shoot thermometer out in the truck, I will record temps at dash vents, floor vents, etc. when we get underway tonight.

My son drives on the way home so I can bounce around the cab and get some readings.



Curious now how much heat makes it comfy.

 

[mwilson]

Here is what I observed on the way home for temps at the dash and floor vents.



Started truck, let it run for 15 minutes with 20 degree outside temperature.



Started for home, temps as follows with airflow split between dash and floor.



Engine Temp *********************** Dash Vent Temp ******************* Floor Duct Temp



140 **********************************90



165 *********************************105



175 *********************************120



190 *********************************125********************************145



Thermostat Open **********************130********************************150



Thermostat Closed *********************126 ********************************145



At 150 degrees on the floor my left hiking boot was smoldering..... :-laf

 

[SRath]

My heater box and ductwork have special internal insulation. I removed it several months ago but it has grown back all on its own. And my heater will roast ya!