Engine/Transmission (1994 - 1998) 12V thermostat

[shendren]

is the upgraded t-stat supposed to be better for my engine. my original is fine other than the fluctuation. thanks. scott.

 

[Cooker]

Hi Scott,



Yes the updated thermostat is supposed to eliminate the fluxuation (sp?).



I am not 100% sure of what the new part number is, but if someone doesn't post it I can dig it up for you.



IMO, The fluxuation is not that big a deal. I have learned to live with it, and as far as I know there are no ill effects from it.



Take it easy,

Ryan

 

[Joe G.]

Ryan,



I agree, the fluctuation is no big deal. My '95 still has the original stat. One thing I have thought about is that in order to dampen the fluctuation the stat has to open slower or restrict the coolant flow some. With this observation I wonder how these old vs new type stats handle a real heat makeing situation like pulling a very heavy load from Bakersfield to Mojave in August. I trust the older style to do the job in this kind of situation. I would worry about the new, no fluctuation type.



Any comments?

 

[PUMPERDUDE]

Save your bucks

I up graded mine when I had to pull it. (piece of slag or casting had it jammed open). Bought the latest/greatest T-stat for the beast from a reputable source. Still seesaws back and forth. Only time it levels out is when towing. Comes with the territory I guess.

 

[illflem]

I installed the new improved Cummins tstat to try to stop the fluctuation. The fluctuation mellowed but the engine ran too cool. I settled for a $8. 95 Stant 190° tsat from Napa. Still fluctuates some but runs closer to 190° now even while towing in the summer heat.

 

[SlyBones]

I am with illflem. the new thermostat eliminates the fluctuation, however it runs on the cool side and warms up slower that the original. My experience anyways. My next coolant change I am gonna try the NAPA one as he suggests.

 

[shendren]

thanks for the input. i bought the improved stat from geno's last night before i looked into the job. i thought it would be like it is on my other vehicles. not. looks like you have to take off the drive belt. i have never done that. are there special tools required? thanks.



scott.

 

[jolyman]

Good luck Shendren on the choice of thermostats.



I had my thermostat "GO OUT" this side of Santa Fe two weeks ago. The dreaded rubber whats-u-call-it sucked up into the opening so it couldn't close syndrom.

I went to Rocky Mtn. Cummins and reasurched the cure. "MY choice between the old thermostat or the "New and improved" #3934373".

I chose the new one -- They look the same but the new one doesn't fluxuate as much and it only gets to about 175 deg. instead of 185 deg. or so.



I wonder why they are made so the rubber sleeve can come loose and be sucked into the thermostat?? Does anyone know what the sleeve is for?? can it be removed before assembly and be done with that problem?



P. S. They told me that they seldom put NEW antifreeze in the units they service -- just test the antifreeze and if O. K. they reuse it --- I chose the new antifreeze and distilled water route with new upper and lower radiator hoses.

I just fell better that way.

 

[jolyman]

Shendren -- I just saw your belt question.



The belt tension is realeased with a 3/8 breaker bar with no socket on it. Insert the square shaft into the SQUARE 3/8 HOLE in the Pulley TENSIONER (DON'T remove the bolt)--the hole is several inches below the bolt in the tensioner mech.

The tensioner is below the alternator pulley.

The breaker bar handle should move to the passenger side of the truck to realease the belt tension.

Remove the belt from the alt. pulley -- don't remove the belt further -- no need (do notice how the belt is threaded in case it falls off).



Remove the top hose and the small heater bypass hose.



Remove the long alt. bracket bolt from the thermostat housing and the other bolt from the other end of the alt. bracket and that frees the alt. top bracket. Then bush the alternator down out of the way a little.



There are two bolts on the top of the thermo. housing and one under the housing. Remove the housing being carefull how it is put together so you get the thermo. back in the right direction.



It is easer than it looks. I did mine mostly with one hand (I had surgery on my left shoulder) GOOD LUCK Jim

 

[shendren]

thanks very much for the input and encouragement. scott.

 

[flexyxj]

I did a search and came up with this old thread....My 96 12v doesn't seem to get warm unless going down the road for 15-20 miles and cools right back down to 140* as soon as you get off the interstate. I even completely covered the front with cardboard with a hole the size of a coffee can and it still runs cool. I'm suspecting it has the original T-stat in it. These symptoms are in 25* - 35* weather. Now is -2*......In the summer it fluctuates some in the very warm weather but stays around 180* if you drive 65-68 MPH. Any faster than that(towing or empty) , it will quickly heat up to 200*-205*....Slow down and it drops right back down to 180* Is this a 12v trait or do I have something else going on?

 

[DonFitzwater]

You could probably use a thermostat and a heater core (if your heat inside the cab is less than desirable.........I run a winter front on the grill AND a sheet of cardboard between the radiator and intercooler to seal off any air movement through the radiator. She still doesn't like to make heat in the cold though (below zero)

 

[GAmes]

With a cared for cooling system and a good heater core a 12 valve will give you plenty of heat. The "improved" t-stat referenced in the first few posts does not stop the gauge fluctuation. Some Cummins t-stats do it more than others, the one I have now fluctuated in WY pulling a 37 ft 5er against the wind. It might have been because the temp was in the 20s. At any rate I get heat within 3-4 miles on the coldest days and have never felt the need to stick cardboard in front of the radiator. I delivered a trailer in Edmonton, AB a couple winters ago when the temp was -14. Coming back to the states with no load on the engine I never had to turn the heat selector knob past the vertical. I didn't know it at the time but the dash air recycle actuator wasn't working, so I had outside air coming in. Genos sells Mopar heater cores. I don't use anything except Cummins t-stats.

 

[flexyxj]

Thanks for the replies. When I can get the water temperature up, the heater will run you out of the cab. According to the Haynes manual, it 's supposed to have a 188* thermostat . All of the parts store that I contacted only showed a 180* thermostat available. With the last 8 digits of my VIN, the local Cummins shop claims to have a 190* thermostat available. I'll know more tomorrow.

 

[GAmes]

I suggest you sign up for Cummins quick serve. http://www.cumminsforum.com/forum/94-98-powertrain/1867106-cummins-quickserve.html

The Cummins t-stat for a 12 valve engine is 180, and works just fine.

 

[flexyxj]

I got the Cummins 190* thermostat installed today. The old thermostat was stuck open because the rubber around the backside of it had partially peeled off and was between the thermostat and the thermostat housing. It was exactly as described earlier in the thread. Cummins is very proud of their thermostat and the rubber gaskets needed to install. It was 103$. Now it warms up faster and the heater works better! Now if I can figure out what/where the airflow restriction is in the dash, I'll be happy....

 

[GAmes]

By checking quickserve for the correct part # and doing a quick interweb search I found this set. There are possibly better prices out there. http://puredieselpower.com/dodge-pr...degree-thermostat-with-2-sealing-o-rings.html

 

[TurboFan]

Since you guys have been working on this recently, can I ask a question?

my coolant appears to be leaking where the tstat housing mates to the lifting plate (lifting hook?).
is there supposed to be a gasket between those two?
the fsm doesn't show one.
thanks

 

[GAmes]

Since you guys have been working on this recently, can I ask a question?

my coolant appears to be leaking where the tstat housing mates to the lifting plate (lifting hook?).
is there supposed to be a gasket between those two?
the fsm doesn't show one.
thanks

The rubber seal for the t-stat goes through the hole of the lifting eye and mates to the block. #10 in this diagram http://www.scheiddiesel.com/images/P/3927305.png

 

[flexyxj]

There's two different large o-rings. One behind the thermostat and one that goes between the hook and the thermostat....