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Cooling system question

2K views 32 replies 13 participants last post by  e.e. cummins 
#1 ·
OK, I was driving home earlier and noticed the heater blowing cold air. This was after my third stop on running some errands close to home. However, what worries me is the coolant temperature gauge never moved in the 15 minute drive.
Now what also worries me is the fact that the radiator is chock full of the green stuff.
I am guessing I should boil the thermostat and discover that it is not opening.
When that happens, are aftermarket thermostats worth a damn, or should I wait until I can get one from Cummins on Monday?
Thanks,
John
 
#2 ·
Sounds more like it is stuck open, not closed. If it is able to flow the entire time, the engine is constantly being fed cold water from the radiator, it doesn't produce enough heat to counteract this so it will take forever to heat up. They must keep the radiator out of the system until the engine has hit 190-200, then and only then can it start to supplement some aid from the radiator in order to maintain that temp, up until that point, the radiator must stay out of the circuit.
 
#3 ·
You might have also gotten an air bubble in your heater core. If your thermostat is stuck open and your driving, your temp gauge will not be anywhere near 190 degrees.

Could be something blocking the coolant lines too. Sludge ect. When was the last time you flushed your system?
 
#7 ·
Not sure the heater core would cause the temperature gauge to not move off of lowest temperature.
I have never flushed the system, only had the truck a couple of months now and neglected to do that.

Pulling the thermostat here shortly. If it is stuck open, it should be open when I pull it, no?
I am assuming the temperature sensor is at the bottom of the radiator somewhere? My worry is that I have had other vehicles that did this same thing and wound up doing some damage. The truck ran fine, but concerning nonetheless.
 
#14 ·
yes, sounds like the t-stat is stuck open

And like mentioned, best bet is a cummins replacement. the aftermarket ones dont have a great reputation
Napa's thermostat has a good reputation in the Cummins. Many prefer it because it maintains a more consistant coolant temperature.
 
#5 ·
First question is how long did you let it warm up before the 15 minute drive? I have an easy way to test this. Start it up cold, after a little bit you will need to hold your hand on the radiator hose just after the thermostat. It will be cold till the thermostat opens, but when it opens that hose will become hot instantly. That will tell you if your thermostat is working. IF its not then it will slowly warm up but not get hot instantly.
 
#8 ·
The temp sensor is at the back of the cylinder head on the drivers side.

Im going to also take a vote for their being air trapped in the heater core. The flow to the heater core is completely independent of the thermostat/radiator.

If the engine temp was reading good on the gauge, their should have been warm coolant circulating to the heater core regardless of the thermostats state.
 
#11 ·
Just replaced my thermostat 2 days ago and mine was stuck open as well, gauge never got above the first line no matter how long i drove it, my heat took about 20 min to get a little warm but never got hot. Bought a new thermostat from auto zone for about $30. My local dodge dealer didn't stock an oem one and they wanted $60 for it. So hopefully the cheap thermostat holds up, if not its got a 2 year warentee. After i replaced it, my truck warms up 100 times faster, i get blazin hot heat now, and the truck even runs better.
 
#16 ·
Cardboard over the front of the radiator ftw! :hehe: yeah, I'm leaning towards thermostat if both coolant hoses stay the same and never get hot.
 
#18 ·
how would one go about getting the air pocket out of the heater core?


my heater core gurgles, just did the water pump/ flushed the system and my heat sucks. sounds like its got some air in it
 
#19 ·
The system is designed to self bleed. That little hose on the thermostat housing is connected to a wobble valve that lets air out of the system. That gurgling you hear happens with mine every now and then. It doesn't affect the heat. You may need a new heater core, are the in and out hoses both hot? If not the core is plugged.
 
#20 ·
the only time my heater core gurgles is when i've had her plugged up for the night. normally never does it. i bought a cover for my front, i just don't have it on yet. i get great heat sittin still, once i start moving she cools down, and yes, i do have a weak water pump, only say that because unless i keep her up around 1200 rpm sittin still the heat cools off. anyway, good luck.

rande
 
#21 ·
Both hoses are hot. Heat still sucks. What else should I look at
 
#24 ·
So they're both hot.

Both hoses hot indicates coolant is flowing through it. The core is plugged with debris.
??? If coolant is flowing through it, its flowing. Which is the inverse of plugged up with debris. Catch my drift?:buttkick:

You mean the fins are plugged with debris?


Does your themostat function? Gauge work? Needle moves? Never heats up?
 
#22 ·
Do these rigs have a Heater Control Valve? If so I would almost guarantee that's it. Otherwise my guess is plugged up heater core. Did you check the hose going in and out of the heater core to see if there the same temp?
 
#26 ·
temp gauge will swing up to about 190, hold for a min, and swing back down, so im assuming the thermostat is working fine.

out of the past month with the truck id say ive had one day where the heat was what id expect, and it involved alot of idling. i also tried putting a piece of cardboard behind the intercooler before the radiator thinking it would help, and as it helped make cruising temps stable instead of swinging up and down, it didnt help the heat.


both hoses are the same temp, and they are both about as warm as the upper radiator hose gets. how do i get into the plennum?
 
#27 ·
while you have all that down make sure that the door that diverts the air through the heater core is functioning properly. I just went through fixing that on my truck, it wouldn't close completely allowing a lot of cold air to come in with the heat so it felt like it wasn't getting hot all. I pulled down all the ducting and such and cleaned it out along with the fins on the heater core. Works a thousand times better.
 
#31 · (Edited)
Not yet it wasn't.
Just took my first drive with the new Cummins stat installed and the temp gauge barely moved and no heat after about 20 minutes.
It is beyond me what else could be causing this.
I mean it is cold here but about 30 so not that cold.

Edit - I'm going to try out the cardboard in front of the radiator and see if that helps.
 
#30 ·
I know that you said that you tried the cardboard trick but you may need more blockage. I swapped the motor in mine last year so the cooling system is clean, new thermostate from Cummins, and a new water pump. My heat still sucked and I had the wide temp swings. I blocked the radiator 2/3 of the way and now have constant engine temps and heat when its 20 degrees out. You may want to block it off a little more than this though. With the block heater plugged in the truck is up to temp in under 5 minutes and running a constant 170-190 degrees. a little cool but a major improvement.
 
#32 ·
did you check the passage in the head for damage on the bypass port?

What about the condition of the t-stat. If you or someone else has decided it was a good idea to leave out the engine lifting bracket during installation, thats an issue! It will crush the t-stat without the bracket in there acting as a spacer!

Does the upper rad hose have any heat? If so, the tstat is not closed fully.
 
#33 ·
Didn't notice anything wrong in the head when I felt around in there. Anyway, why would that suddenly be an issue?
The lifting bracket was reinstalled.
Again, the upper and lower radiator hoses were warmer than ambient, but pretty equal and not hot by any means.
I ran the truck with the radiator cap off to look for obvious signs that their was coolant flowing at the low temperature and it seemed to be perfectly still.
I am guessing the radiator blocking is going to help, but the roads here are pretty icy currently and I don't want to go for a test drive.
 
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