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Discussion Starter #1
96, mostly stock, automatic, will not warm up. It was -36F this morning, pulled out of garage, idled 25 minutes, heater on recirculating mode, cab has chill off but windows fogged up. Drive 15-30 miles 50-65 mph and the highest it gets on the gauge is about 150-160— Cannot keep the cab warm. Radiator has three plastic panels blocking air flow, one on each side between radiator and intercooler, and one in the center in front of the intercooler. Fan is still on and may be contributing some. It didn’t heat well last year, but this is worse. I believe I still have a 195 thermostat in it. If the thermostat was not operating as it should, I would have a hotter upper hose. (New aluminum heater core)

I got home pulled it in the garage, felt radiator top hose- cold, very cold. Felt fill side of radiator (lower hose side) and it is warm...??? Twenty minutes later in a cold garage, I shot temps with IR thermometer. Lower hose was 75 degrees F, top of radiator (lower hose side) 62 F. The whole passenger side of the radiator was warm. Upper hose near thermostat 37 degrees F, radiator (upper hose side) 27 F.

Is this just expansion from cold coolant being warmed up? I guess it has to go somewhere as it expands and with the thermostat closed, it would have to back up into radiator. ( Upper hose has pressure)

Thoughts?
I think I’m going to have to park it for a month.
 

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It sounds to me like the t-stat is stuck open or opening long before it should. A pot of water and a candy thermometer will tell the tale.
 

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Discussion Starter #3
If it were open, the top hose would be warmest. The top hose is cold
 

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It certainly isn't stuck closed as you suggest. If it is the engine would get a lot hotter and you would have corresponding heat.
 

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Discussion Starter #5
At -36F, open just a crack would allow the upper hose to be warm. I cannot believe it is open at all. My pyrometer shows 250-300f at idle 600f at 50-60mph. I don’t understand how it cannot warm this engine up. I can watch the temperature gauge go down when I flip from recirculating to defrost. So my heater core is pulling heat from the coolant. I know the transmission pulls some and I have a deeper pan, but still, why won’t this get hot???
It’s warmed up now, it’s only -29 so I’ll go out and check it. NOT.
I think I’ll sit and look at houses for sale down south.
 

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1 piece carboard blockoff the same size as the radiator less an inch or so on the sides & +an inch or so on top(for rapid removal) cut 6" circular hole in the middle for fan clutch. Now it will heat up & open the thermostat & it might heat up too much hence the reason for the rapid removal of blockoff, at which time you'll have to experiment a bit as to how much more airflow is needed to maintain comfort for you & the Cummins. These engines @ -36* outside ambient air temp, just cruising @ highway speeds are not generating much heat, the exhaust gas temp is going out the exhaust not into the block. It has been my experience that it is easiest to control airflow w/blockoff by working/trimming the top corners. Watch your temp gauge in traffic or slow moving operation. By the way your diagnosis is correct that the t-stat is not opening.

As a side note, one of the variables in determining a GVW rating is radiator size & capacity.😉🇺🇲
 

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I think I’ll sit and look at houses for sale down south.
I'm on South Padre Island right now, you can't really get any further south without a passport. It's cold and crappy here too. Though no -35 :D

Your bypass check valve may be stuck open.
 

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Discussion Starter #8
I was looking at properties in South Alabama and Texas on the coast and came across a sit with the weather temperature posted. It said 30.1 degrees. I figured it was Celsius, but it was Fahrenheit. That was on the water. You know it’s all the wind power farms up here just trying give Americans ice to skate on.
 

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Discussion Starter #9
My description tells you I have the radiator completely blocked off, just the thickness of the intercooler and condenser allows a slight path of air on each side to relieve the fan. I could heat up the garage and investigate but it sounds like I will be busy a few weeks driving so I’ll wait until it’s cheaper to warm the garage.

I noticed a little coolant on the floor when I moved the truck out today, so I have a few things to address. I would be happy to never deal with this again and live in the south.
 

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My description tells you I have the radiator completely blocked off, just the thickness of the intercooler and condenser allows a slight path of air on each side to relieve the fan. I could heat up the garage and investigate but it sounds like I will be busy a few weeks driving so I’ll wait until it’s cheaper to warm the garage.

I noticed a little coolant on the floor when I moved the truck out today, so I have a few things to address. I would be happy to never deal with this again and live in the south.
Radiator has three plastic panels blocking air flow, one on each side between radiator and intercooler, and one in the center in front of the intercooler.
I was having a difficult time envisioning your description. Only relaying to you what works for me on my 96, 1 piece full blockoff 'tween rad & intercooler.😉🇺🇲
 

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Discussion Starter #11
Last year I had it full blocked and no fan most of the December through March. I use three pieces and slide them over or remove when temps get warm. Fully blocked I could go down the interstate at 75 mph at 32 degrees and not go over 190. You do have to watch. When the swings are barely moving, you know you better open it up a bit.
 

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There's no such thing as 195* thermostat flr a 12v. Its probably the wrong one and not working right.
 

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Discussion Starter #13
Several 190-195 thermostats fit and function fine. I didn’t say what thermostat I had. They are not designed to fully block off the recirculating pathway as a Cummins thermostat does. But they open at the proper temperature and coolant takes the path of least resistance- to the radiator. Towing in warm weather I would want the Cummins design. For winter time, the 195 without the “puck” that extends to block the recirculation port is fine. It’s worked fine for three years.

The reason for the post was that it threw me a bit that the lower hose was warm but not the upper hose.
 

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If the radiator is warm and the engine is not at temp.... the thermostat is not working.

The engine will warm up eventually even on the coldest days.... if the thermostat is stuck open, even partially open or allowing coolant to flow because its the wrong one........the truck will probably never warm up.

Put a cummins thermostat in the truck and report back.
 

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Discussion Starter #15
Respectfully, I don’t think you’re reading the post. An open thermostat, even a partially open thermostat, would leave a path for coolant to return to the radiator via the upper hose. The upper hose is cold. The left side of the radiator is cold. With an open thermostat, the upper hose would be the first to get warm.
 

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I have heard stories of the auto trans ( 17 quarts of fluid ) sucking all the heat out of the engine via the water to oil heat exchanger in extreme weather , engine never gets to OT and dismal heat , ect ect .
Fact or fiction , i dunno.

My 94 with a recent 5 speed conversion has BANGING heat , i will sell or rent you some BTU's.

Still say your thermostat should regulate engine temp no matter the temps . A winter or summer thermostat is BS . One should not have to swap them for the seasons .
I am running an aftermarket non Cummins thermostat marked 190* that actually operates at 190-195* and while it takes a solid 20min to get to OT it stays there in that swing 24/7.

On my 01 i ran several thermostats
Gates = The worst wild swings ever witnessed .
Cummins = Pretty good swing , for what they cost , they shouldnt
Napa HD = acceptable with swing . So i ran that one.
 

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My stick shift truck definitely throws more heat.... and the auto you can feel the difference when the converter is locked and not making any heat.... sucks the heat right out of the engine.


Feeling hoses really isn't reliable for measuring temperature.... if your confused ( I know i am) stick a thermometer in the radiator and see whats going on.... again I suspect thermostat.
 

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Discussion Starter #18
As mentioned. I checked with an infrared thermometer. Upper hose at 27 degreeF after 25 minutes warmup, 15 miles at speed. It is not letting anything through except what goes through the bleed hole.
 

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The thing I don't get is why the lower hose is significantly warmer. All I can think of is that there is a lot of air trapped in the system? If you squeeze the upper hose it seems full?
 

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Discussion Starter #20
The system is full, the upper hose is full. I put forth my guess: the coolant in the block and heater/ transmission cooler has to expand and go somewhere. With the thermostat closed it has to go through the lower hose. If I had air, I would be getting a hot temperature gauge.

I don’t think you realize how cold it gets here.
 
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