Alright been messing with this for a couple of weeks. Started when it first got cold. Noticed my heat was not as warm as usual. I checked my radiator and it was about half gallon low. After I filled it up I drove it and the heat seemed to be better. When I got home I noticed some antifreeze on the ground. Looked up there and found it dripping from the drain plug. Replaced the plug which I might add is a stupid design and pretty much worthless to actually drain your radiator. Why cant it be a pitcock drain. NOOOO it has to be some nasa frickin design with an O ring that doesn't actually work after you remove it the first time. :banghead: Sorry !! Anyway it wasn't the plug anyway but a leak in the radiator up a little higher behind the shroud. Ok now this is where I get lost. This is a closed system and it will build up pressure. Why is it just dripping ? Why isn't it spewing out making a mess ? Ok so I get a new radiator and install it. Replace the t-stat got it at O'reilly's and flush the engine and then disconnect the heater hoses and pour some clr in the heater hoses and let it sit in the heater core for about and 1 1/2 hours and then flush the heater core and reconnect the heater hose. Then fill the truck up with water and then I let her run a bit cause I want to make sure I am getting flow thru my heater core so I pull the hose off on the block side of the heater core and it is pumping good then I pull off the hose on the other side of the heater core and it comes shooting out. Then I drain it again and put the truck on slight upward hill and refilled with antifreeze. Also replaced the resistor on the blower. It went out in the middle of this. Also checked the door where you switch from AC to heat it works fine. Also checked the temp selector thingy underneath there it corresonds with adjusting the temp control. It spins around and stops.Take her for a spin the truck heats up to 190 heater seems warmer ? This truck has always heated up to 190 and would move a neeedles width either way while driving. The heater has always been hot and usually if I have plugged it in after a ten minute warm up it was very toasty. Ok now that I have replaced everything the truck is very slow to reach temp at idle. While driving @ 60mph my truck will reach 190 or just a hair more but when I slow down for a stop light the temp drops down to 160 or so and then as I accelerate the temp will slowly work back up to 190. My heat is warm at best but by no means is it hot. I just left work idiled in the parking lot talking to my friend for about 20 minutes and then drove home from work 25 miles mostly 60mph. I get home and pop the hood nothing is really hot at all. The radiator is not hot or even really warm. The upper hose has some pressure on it but it is not hard to squeeze. It's warm but not real hot. The heater hoses are a little warmer. So I touch the cap and it's not even warm so take the cap off and there is just no pressure at all I look into the radiator it is still full and there is no flow in the radiator at all. I feel stupid that I can't figure this out. The heater prob could be the core. But when I pulled the heater hoses I had good flow going in and out and the water was hot. (ouch dumbass). So I am thinking it is not the core. Why is there no noticable pressure at the cap ? Why is there no real pressure in the hoses ? If it is not pressuring up you would think you had a leak ? But I don't. Why is the temp of the water seemingly not very hot ? T-stat staying open ? Then I would think I would see the antifreeze flowing thru the radiator ? But I don't. Water pump not working ? Then I would think the truck would over heat or at least get hot ? It doesn't. For some reason the cooling system is not getting hot enough. It is not creating any pressure either. It is not cold enough here to require blocking the radiator. Never had a prob before. I am sure it is a simple fix but I am just at a loss as to what ? Why does it get to 190 and then drop back so far ? Why will it not hold the heat. Before it just stayed at 190 within a needles width either way. Sorry for the long post. Any help would be appreciated. Thanks Rob

I don't know why we have so many posts about this issue but I will try and collaborate on it with as much info as I can think of. It is obviously a very common issue..First of all, you said when it leaked it would just drip, not spew. It probably relieved all the pressure out of the hole as it warmed up so it never got to the point of spewing. A bad radiator cap could also be relieving the pressure by not sealing correctly or just being warn out. The water pump's flow will not be seen in the radiator. You might see a rise and drop of coolant if it had some air in the engine that it purged out, otherwise it will do nothing but increase in volume as the temperature of it increases and eventually relieves to the overflow. The thermostat is the thing I am questioning. If it is screwed up in any way shape or form to where it stays open a little or a lot, it will take forever to heat up and if it stuck fully open, it may take 20-30 miles for the engine to get to 190. Once it reaches that temp however, the radiator should be pressurized regardless of the thermostat's condition as long as it is opening or stuck open. If it is stuck closed then the engine would overheat which doesn't seem to be the issue. From what I could tell the air for the HVAC goes through the evaporator regardless. If the evaporator and or heater core is caked with dust (like mine was) you will have less flow of air coming through the vents, if it is the heater core that is caked then obviously the air won't be able to blow through it and get hot. It can also be caked by a small coolant leak on it and that would build all that green fungus looking stuff all over the heater core. The whole system should pressurize and if it doesn't you have a leak somewhere. I would keep an eye on the overflow tank and see what it is doing. You can get a radiator tester to put where the cap goes to find out of it is pressurizing at all and find out of it is the cap that is bad.

Are you from Iowa?????? With a name like Hawkeye, I have to ask, because your profile doesn't say where you are. The cooling system on these trucks is amazing due to their size and capacity. My 04.5 will cool down to 160*F and less from 190* if I let it idle in cold weather. I would surmise also that if left idling long enough, there wouldn't be any pressure in the system, because the coolant temp is below boiling. My 04.5 won't and my old '99 wouldn't "warm up" to operating temp at all in cold weather.Get a quality brand thermostat and swap it out. It's the easiest/cheapest way to go. Winter front??

Ok... A few tidbits to add... The 190*F stock thermostat is basically closed by 188*F so at 190*F it barely cracking open. If your looking in the radiator for movement its not going to be there. When you'll see movement clearly is on a super hot day and the coolant is at 198*F now you'll see flowing coolant because there thermostat is fully open. As for the heater core test flow by grabbing the hose is not a true test I hate to say it... I had this exact problem with my 1972 Dodge PowerWagon pickup what it came down to was pulling the heater core and rodded it out. trust me after doing that it worked awesome. But in the same sense I had a plugged heater core and was doing the same thing feeling the heater hose lines and they were both hot assuming that it was flowing... Nope they weren't flowing good at all... Its convection of hest it was heat the coolant regardless of the flow. Now truely if the heater core is working propelry there should be a few degree fall on the return line but on a plugged heater core both line will most like feel the same... Because if the heater core is dumping heat in the cab the return should be cooler. Just like the radiator the upper hose will be hot as hell and the lower hose is cold to the touch this is showing that the radiator is doing it job properly. So my thought is heater core is still partially plugged up...

Get a T- stat from cummins and a good name brand rad cap from place and see what happens. It cant hurt and its cheep enough.

I need one,is the pressure cap 16lbs from the factory?

I need one,is the pressure cap 16lbs from the factory?

I had the cummins specs up the other day from quickserve and the 210F cooling systems was 7psi cap and the 220F systems ran a 15. That is on my 12V though.

I asked for a new cap at NAPA a few weeks ago and they gave me a 16 I got a 195-207F thermostat now so I guess everything will be compatible now.

Alright here it is. This is using Mike's engine number, figure it would be the same as yours. So I guess I am not sure what was factory.

It is unusually cold out this week. Do you have cold weather fronts installed on your hood grill? The may or may not be a big part of the problem but if I forget to install the cold weather fronts on my and wife's truck, they both take FOREVER to warm up and will not hold heat worth a flip.

Sounds like a bad thermostat to me. Have you checked around the head for leaks? A leaky head gasket can cause these things too.

Sorry I have been busy and haven't gotten back. Last Wed I went to napa and got a new t-stat and radiator cap and installed both. It seemed to fix the problem. My temp gauge went to 190 and stayed right there and I had heat everything was back to normal:hyper:. On Sat morning got up to go to work warmed the truck up temp gauge was normal but I had NO HEAT:banghead:. Drove to work my engine temp was normal 190 and stayed there. Sat nite I am getting ready to drive home and I am messsing with the selector and I turn to max ac and suddenly I have hot air. I drive home and if I switch it back to the regular heat it just goes cold. Almost like it is letting outside air in. So Sunday morn I get up and same thing if I have on max ac I get heat. Sunday nite my Gf comes by work and we are driving around and I tell her my heat only works on Max AC and I switch back to regular heat to show her and now it starts blowing hot air again. So I drive home and everything works normal again. On Sat when the heat only worked on Max AC I checked to make sure the flapper door was working and the little rotating thingy down by the passenger floor was moving correctly when you moved the temp selector. I am just at a loss to explain this. Thanks Rob

Unless you heater core is partial plugged up and the outside air is so cold it can't heat it. That's why on MAX A/C (recirculated air) it has heat but in all other positions the outside air is used...

mopar this is driving me crazy. This is such a simple system to diagnose. LOL you keep coming back to the heater core. I do not mean to be hardheaded and I take your and the others advice seriously. But the part I don't understand is why the heat works so good sometimes. It was definitely cold here Sat morn 14 with a nice windchill but it has been just as cold when the heater worked perfect. To remove the heater core is a chore for sure but I would be more than happy to do it. I have to be honest I have dealt with this prob before in other trucks I have owned and in the end it was always the heater core. After rereading my post I guess I am being hardheaded. I mean everything else seems to be working it has to be the core Since it is working now I will ride it out and see what happens and just plan on doing the heater core when it warms up. Thanks Rob

Hmm I was just flipping through reading a few posts and stumbled across this. This seems to be just like my problem to an extent. I actually just posted a thread on CF about this. Maybe someone from here can give me some insight and maybe we can both figure out our problem. http://www.cumminsforum.com/forum/98-5-02-powertrain/353230-cooling-system-issues-radiator-not-hot-nor-building-pressure.html