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dually

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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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.

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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.

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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:

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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?

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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.

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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:

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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...

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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:

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

Always gotta be difficult :mad:

Posted Image

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Just thinking of that what did you do about jiggle pins? Curious what you had to do to make it work?

Jiggle pins? The stock one is a lot wider, it is just as wide in diameter as the whole housing so it barely comes out if rust forms. You put a gasket in that is just as wide and then the thermostat on top of it, then another biggg gasket, then the engine lift bracket. The new thermostat was not as wide. It did not sit on the machined edge on top of the gasket, it was about 1/4" smaller diameter. However, it fit perfectly inside of it on another surface, like it was meant to be there. The only thing was sealing it off. I couldnt use any gasket under it but I used that bigger gasket which by big I mean it was the same diameter as the housing, but was really thick so it would cover the edges of the new thermostat. So I just threw it on top and made it so the engine lift bracket would smash it a little, which is actually how it is supposed to be on the oem thermostat as well so it wasn't really rigged. Then I bolted it all up. Works like a charm.

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What parts do i need when i take my dash out.I will replace the heater core and the condenser for the ac.What is the flapper door part?

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What parts do i need when i take my dash out.I will replace the heater core and the condenser for the ac.What is the flapper door part?

Well normal tools to get the dash out of the way... But to release the A/C lines you need the special collar tool to do it... http://mopar.mopar1973man.com/cummins/2ndgen24v/hvac/evaporator/evaporator.htm post-2-138698173509_thumb.jpg

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Jiggle pins?

The Cummins thermostat incorporates two pins on either side of the thermostat that allow air to escape up thru the thermostat into the radiator to bleed the system of air. From the reading I have done most folks have issues with non-OEM (Cummins) thermostats. I also have found that our engines are very hard on thermostats. The cooling system is so large that unless your always loaded the thermostat only has to crack open to keep the block full, it takes a lot of heat to get it to fully open. This causes wear spots on the thermostat, which if they get bad enough can limit the amount the thermostat can open. This also fatigues the spring and makes it slow to react, causing the huge temp swings. Before I replaced my thermostat last winter I would get to 202-206 on every initial thermostat opening and drop into the high 180's. Now I get to about 193-195 and drop to about 190 in the summer and high 180's in the winter. My thermostat was only 5 years old with 52K miles on it, nothing crazy.

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