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Cummins thermostats

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Do the cummins brand of t stats have a fail safe?The question is when they go bad are they made to brake in the open position? My engine gets hot 190.The t stat housing is hot. The radiator fluid is cold.I am thinking water pump. The radiator and heater core were flushed in summer.

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  • Owner

Do the cummins brand of t stats have a fail safe?

No... My first OEM orignal failed closed and started to get to hot.

The question is when they go bad are they made to brake in the open position?

Kind of hard when its got a spring pushing the valve closed. Unless the spring fails.

My engine gets hot 190.The t stat housing is hot.

Normal. If your reaching this temp your fine.

The radiator fluid is cold.I am thinking water pump.

Take the truck out for a ride. Return home and carefully open the care with a rag. Remember this is under pressure and could contain hot water. But once you got the cap open look and see if the coolant is moving. Also is the upper hose the same time as the thermostat housing? The lower hose or the cap side will always be considerably cooler.

The radiator and heater core were flushed in summer.

Another suggestion is to replace your thermostat every time you flush the system this just makes sure there is no future problems.
    • Like 1
    • Author

    Well i put a new t stat in and a water pump.I have heat.To me it could be better.This truck from day one never gets hot to the point you can drive with your coat off,Today it is 20*.It is way better than yesterday with no heat. When i feel the air down at the floor and turn the heat knob to full cold it changes to cold and when i turn it to full heat it gets warm so to me the flapper door is working.Is there a way i can see down there to see if the flapper is moving all the way?? Yes to your last question.Also the heater core hoses are both hot so it is not pluged.

    This truck from day one never gets hot to the point you can drive with your coat off,Today it is 20*.

    It was 20F here yesterday too and I usually get 100F over ambient out of the vent next to the radio (so 120F yesterday). That is on just regular, if I put it on recirculate it will get up around 150-160F. I aim to get it so hot that I take my shirt off, figure if it is going to be an arctic day outside it is going to be a desert day inside! :lol:
    • Owner

    Last time I measured my dash vents I was blowing 147-156*F out of the center vents... But let me pull out my thermometer again and check again with winter cold weather...

    • Author

    So maybe my flapper door is bad?? It moves from hot to cold maybe not all the way? Do i have to pull the dash for that?

    at 35F-40F out door temp, i get 120F out of the vent next to the drivers door with it blowing out the vents and floor. i was going to measure with just the vents but couldn't take the heat.

    • Owner

    As for the stepper motor that can be dealt without pulling the dash but if there is something interfering with the door moving like debris you'll have to pull the HVAC out..

    • Author
    http://www.heatertreater.net/ So this may help me if the motor works.? I just looked and mine moves when i turn the heat to cold/hot.If it still moves all the way i dont know.Can someone tell me the normal travel on this motor?
    • Owner

    It not much really... post-2-138698173461_thumb.jpg Look closely the blend door is in the full cold position now. The long flap would rotate up and to the left to divert the air through the heater core. So the shaft moves about 45* angle at the most.

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    • Like 1

    I can never take my coat off in the dodge, will start with a flush and thermostat for now and see if it works for me too

    • Author

    I may have to take the dash out.My down pipe must have a leak and the bummer part i can smell diesel exhaust in my cab now.It was never like that before i think the door or whatever is not working so well.:banghead:

    • Owner

    I can never take my coat off in the dodge, will start with a flush and thermostat for now and see if it works for me too

    :stuned: Hua??? Heck I got to leave my jacket in the back seat or I'll fry to death in the front... I've seen cab temps of 100*F before... (Not Vent!) on a 20*F day...

    I just fixed all that gauge swaying. Put in a new thermostat (this one) and now it is perfect. Before, it would go to 220 then drop to 150 and just keep doing that crap but closing the range, so then it would go to 215 and drop to 160...until it steadied around 190. Now this new thermostat isn't even for the cummins, it's for the 5.9 V8 gasser. I had to rig it a little to make it work. But now it heats up faster and goes to 200 and slowly goes down to 195 and just goes between that 195-200, none of this initial 220 then 150 BS. It works like the damn thing is supposed to! Now I boiled the other one and it was fine so I don't get why it was such a POS. There is something screwy going on with the cummins ones you buy but I can't understand what. So much nicer knowing it goes up to proper temp and holds rather than all the swaying which can't be good for the engine, kinda like dumping a bucket of cold water on a windshield that has been in the desert sun all day. Oh and that one is a superstat, so I am all for them now :hyper:

    Part link didn't worky... You need to make a screen shot of it... :rolleyes:

    Always gotta be difficult :mad:

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