So did you check the bushing, that connects the blend door motor to the blend door, common problem that they crack and motor shaft spins in bushing and blend door does not move.

 

missouriman, Does your temp gauge read 180 degrees after running a while? Or does it never go that high?
I did almost all that you did, No heater core though, Checked flow it was fine. This was my solution, I Put What's called Fan Fold, in front of,just the radiator, Fits great, I have been doing this for 8 years, I Live in the north east and it's also been Cold here this winter, We have been getting hammered with snow, Cold. I just have to remember to remove this when it's over 30 degrees or the truck will get warm it never has over heated, I get good heat even at zero degree days.It runs with the gauge right at 180.I have about 7 inches of radiator not blocked.

 

^^^I did that and cooked the coolant out of my A/C system....no airflow through the fins= $225 to recharge after it blows off!!

I'm still thinkin' its the blend door hanging up...

 

Yes I saw that in your earlier post.Did you block in front of your AC Condenser or behind it and in front of Just the radiator? And I use my Defroster all the time, And AC works in the summer. I have been doing this like 8 years, I have plenty of space for air between the fan fold and air for the AC Condenser and the intercooler.
If his engine is not getting hot he will not get heat no matter what, Blend air door or not. I know mine would not get to above 150 degrees and that was not heat, Well it was when it was -4 degrees outside. That's why I do this and it works great. That why I asked him what his temp gauge is at.

 

the gauge reads just off cold at idle, warms up going down the road.

when it gets warmer out I will check all the flow doors.

 

You can check all the doors you want BUT if your engine is not getting hot you will not get any heat, Your gauge should read about half way,Which should be at about 180-190 degrees.
Block that radiator just like I did in my photos,even just for a test, get that engine hot,Make that gauge go to 190,THEN see if you have any heat,If Not THEN I would look at the blend air door.
It was zero here today and Mine just got to 180 degrees after driving 20 min,And first letting it idle on the 3 cylinder idle up for 15 min.
The 3 cylinder idle really helps alot,BUT it sounds likes engine is going to blow up.

SPRING Time is Coming, Just not fast enough.Supposed to be 40degrees here Friday
Might have to break out the suntan lotion and the lounge Chair.

 

I have the radiator blocked like you do, And I have everything blocked from head light to head light, hood to the lower curve of the bumper with a second piece of card board in front of everything.

It will get up to the 180 range going up hill or down the road. But if I let it idle it will get below the first mark on the temp gauge. It will stay warmer shutting it off rather then let it idle when taking the kids into day care.

EGT going down the road are in the 500 to 600 range. going down the mile long 6 percent grade into rapid city on hwy 16 they can hit a low of 200. I can watch the temp gauge go down.

I have tried 3 thermostats, dodge, napa and Cummins.

I am running number 1 fuel oil, burns cooler, less power, less miles per gallon but will start at 18 below, got to try that the other morning.

 

Truckman: Yes I had a thick piece of cardboard with an 8" diameter hole cut out of the center to aid the fan clutch. My A/C guy said blocking it in this fashion reduces airflow significantly through the fins of all three coolers, the a/c, the intercooler and the radiator. This popped off the a/c condenser valve when the cooler overheated from lack of airflow. Blocking airflow off at the grille is the best way to go, like the big rigs do, allowing airflow, just not a direct blast...

Missouriman: even if your truck is pulling off the 140 mark, you should have heat in the cab. Set a small heater at 140 and see how long you can keep your hand in front of it!

Even at 0 degrees F in MT last winter w/o the radiator blocked I was seeing decent heat, still getting to 190 on the gauge before the t-stat opened and dropped it down to the low range side.

Most of the heat generated when running goes out the exhaust, unfortunately, I'm still thinking your blend door is allowing colder denser air to lead thru the system.....

 

I agree sixslug, Just with that 8 inch hole in your cardboard is not enough air flow,And also agree with the electric heater and burning your hand at 140*, But just because your temp gauge reads 140* you will not get 140* out of you air ducts, I have 2 seperate pieces of 3/8 fan fold (styrofoam) with about an 8 inch gap from the top of the radiator to the bottom of the radiator open, And it's not laying flat against the radiator,See pics in my other post, Plenty of air flow for the ac condensor, and the intercooler, I did a test on the way in to work today, It is 22 degrees here in the North East USA today (warm) so the results would be a little different on a zero degree day, at 5:15 this morning started the truck let her run about 15 min, Stuck my AC/Radiator thermometer into the center duct just above the radio, Started on the highway to work, At about 150* I had 75* heat into the cab, At about 170* I had about 90* into cab, After 25min down the highway at 190* I had about 120* in the cab. Now if it was colder out I would lose more heat from the heater hoses between the block and the heater core, Had to open the windows after that starting to sweat.
Like I say I have been doing this for 8 years now, Cause I was banging my head against a rock trying to figure out why my truck runs so cold, And that was my solution after checking all that has been mentioned here, Blend air door checked, Heater core Checked, 3 Thermostats check, Radiator flow checked,Heater hoses checked.My problem was the engine was NOT getting hot enough.
I thought I did something wrong when I changed the engine 8 years ago, I put a 2001 commercial Cummins engine ISB 185 in my 1998.5 truck from a 50 passenger rear engine Bus with 8000 miles on it that caught on fire, It just runs so dam cold. And what a steal at $1700.00

And this works perfect for me, You may find a different fix.
Missouriman: Let us know what your fix is.
SIXSLUG: Where does your temp gauge run at?

Stick a thermometer in the vents to see what you get.

 

I have been looking for one of those little vent thermometers.

It is going to be pretty nice here on Thursday so I will see if I can check the vent doors with out taking the dash apart.

I have two car seats to mount also maybe I will take pictures of that install. extended cab doesn't leave much room.

 

http://www.harborfreight.com/1-inch-...ter-46586.html
Oh Boy I dont know if I can post this like that,
Admins sorry bout that

 

I have been reading this thread and it sounds like you have it air locked I would try running a garden hose through the heater core from one line and to the other and when doing this make sure your truck is pointing up hill. what your saying to make me say this is your temp gauge keeps dropping to low as if air is passing the temp probe

 

Yeah, I used a piece of thick stock cardboard that spanned the entire radiator, except for the center hole I cut out...I can see yours is gapped in the center. Mine was a hack I came up with to increase warm up time and get the oil up to temp on short trips. Your idea looks to be a better design!

How about a probable open thermostat? When mine went out I ran around halfway between cold and the left side of the normal range on the gauge and remember I had to have the heat cranked to feel any....New Cummins stat fixed that problem...

I have also read of hi mile water pumps losing their fins to the point that they won't circulate much water, but that is attacking from a different angle, but not too hard to check out...

 

Now more info comes out, the head gasket may be different on commercial applications allowing water flow in a different direction in the head to check this check the engine number on the plate with cummins and compare it with yours required for you truck

 

My truck is fine it's missouriman we are trying to help out,

And beleive me Before I Bought and installed this engine I had Cummins America on speed dial, With engine numbers of Both engines.
The Only real difference was The ISB 185 has a cam for more torque on the low end,, YEAH Like it needs that.