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Junior Member
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56 Posts
Discussion Starter #1
ok so i have a problem. I have no heat in my truck, if i keep the blower on low i get some but its barely enough to defrost the windshield. all hoses get hot, radiator gets hot, has a new water pump, heater core, thermostat. the blend door works too. i am completely lost as to what is wrong. it started a year ago when i drained all the water out and put antifreeze in it. since then i dont have heat. if anybody has any other suggestions as to what it could be it would be greatly appreciated. though the winter this year in lower michigan has been fair, no heat still sucks lol!
 

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69 Posts
My 89 doesn't have a real good heater either,but it does eventually get hot,i always thought maybe it was because of the size of the cooling system,but i'm wondering if maybe there's a obstruction in the heater core restricting flow,anyone else have good heat or slow heat.
 

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Are you getting good coolant flow through the heater core? If your heater valve is not opening all the way it won't get the core hot enough to heat the air blowing through it. Pull the return hose off the core to see.
 

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56 Posts
Discussion Starter #4
everything seems to flowing good. what does the heater valve look like? and is it possible to put the hoses on the core backwards? i didn't know it there was a rhyme or reason to which way they went on. i have noticed that the hoses coming out of the core are still squeezable when hot, shouldn't they be a lil harder to squeeze while its hot?
 

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I would say your function control is working if you are able to switch between defrost, floor ect. But it sound like the heat blend door is not. It should be a vaccuum/ or electronic motor on top of the housing that the heater core is in. This door opens and closes when you switch it between cold and hot. Hope you are able to get heat!
 

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Discussion Starter #6
my blend door is cable operated, there is nothing else on top of the heater box. i pulled the blower motor off and could feel the blend door moving and could see it moving with a little bore scope camera deal that my buddy had. let me ask this, would a regular core work in a high output box? i have the high output heater but not 100 percent sure if the core is high output? would a h.o. core only fit in the box or would the regular one fit too?
 

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What about your radiator cap,is the system pressuring,does overflow tank rise and fall with the warming up and cooling down of the engine a unpressurized system wont heat as good,just some more suggestions.
 

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Thought of something else, what about the check ball in the thermostat housing,is it moving freely or plugged,the check ball purges the system of air.
 

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Discussion Starter #9
well i have put a new rad cap on, but did notice the other day that there was steam coming out from it a lil bit after it got hot. the top rad hose gets almost rock hard when it at temp though so i would think that its pressurized. i didn't see much movement in the overflow tank from hot to cold. the check ball does move i remember hearing it when i replace the tstat. now does the tstat have to be oriented to the check ball in order for it to purge the air?
 

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4,247 Posts
Are BOTH heater hoses "HOT" when the engine is fully warmed up and the fan on low? If not, the heater core is plugged.

Another possibility is that the AC system is running all the time, if you have it.
 

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56 Posts
Discussion Starter #11
yeah both hoses get hot when up to temp.. to the point where you don't wanna hold onto them very long, truck doesn't have ac, i'm dumbfounded, to me it seems like there is no reason this truck shouldn't have heat!
 

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Discussion Starter #12
another thing, do you think i should try to switch the way the hoses are hooked up? maybe there is something obstructing it just not real bad? reversing the flow might flush it out
 

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You could try it. If you pull one hose and you have good flow, then the problem is in your air ducting.
 

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Discussion Starter #14
what do you mean the air ducting? i get lots of air out of the vents, just not hot, or really even warm air for that matter, its the warmest while its on low. anything higher for the fan setting and you can actually feel the cab cool down.
 

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OOPS! Sorry forgot that part. Did it work before all the parts were replaced? Does it cool down more when it is being driven? I would still check the flow throught the heater core. It could be restricting flow.
 

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Discussion Starter #16
well over a year ago when i did the motor swap i was just running water in the system, when i moved to michigan and didn't have anywhere to plug it in so i flushed it and put antifreeze in it. i had great heat with the water, after switching to the antifreeze i lost my heat. that's when i started replacing part cuz i figured something wore out. i took it too a radiator shop that couldn't find anything wrong with the system. said he didn't know a whole lot about these trucks but that this problem on a gas vehicle usually means a cracked head. i dunno, i don't have any issues with the truck running, just heating.
 

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You might try taking the cover off the heater core inside the truck,bring the truck up to temp and see if the heater core feels hot,if so its in the air ducting,maybe iduno,just a thought.
 

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Is the plumbing to the 6.9 the same for the 7.3? I know it should be, but I did an engine swap a few years ago and the newer engine had a valve for the heater hoses that made a difference on my older truck. I ended up removing the extra valve and it worked fine. But I am pretty sure the 7.3 is the same. It was just another random thought.lol
 

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Discussion Starter #19
ya know i have read somewhere about a valve on the 7.3s. then i also read the the 7.3 had a flow restrictor built into the fitting that comes out of the block. i guess this is to cut down on the pressure in the hoses and the heater core. i dunno, doesn't really sound like something could go wrong with it as its just the size of the hole in the fitting.
 

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Super Moderator
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4,247 Posts
I just put 270 miles on the '93 7.3L IDI, it will ROAST you out of the cab with even the slightest movement of the dial off of full cold.

Engine fully warm @ idle, temp setting full hot:
HVAC Fan Low: In hose HOT, out hose HOT (you cannot hold it)
HVAC Fan High: In hose HOT, out hose warm (you can hold it)

There is NO WAY both hoses can be hot AND have a flow restriction of any kind. There is a problem with the bland door, either the cable is bad, the lever broken or the door stuck and maybe some combination of all.
 
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