Engine/Transmission (1994 - 1998) Thermostat help

[schlite60]

Many thanks



Many thanks guys for the part numbers, advice and the new part number on the revised themostat. That is on order should be here tomorrow. I am also using the premix Cummins antifreeze too after a really good flush. See how it is after a year with about 30k miles on it! Thanks again guysOo.

 

[akline]

Originally posted by illflem

If you pay attention to your pyro you will see very little correlation between coolant temp and egts. Your engine's running plenty warm even if the coolant doesn't show it.

What the "problem" boils down to is that many folks are barely using the designed power of their CTD just cruising around empty and could get by with a Subaru sized radiator. With the large built for a load radiator we have the coolant sits in the radiator getting cooler and cooler till the stat finally opens for just a second causing the temp swing in the coolant. Like I said before the engine temp is still steady.

I want my gauge to behave this way so that when I do load the truck up the coolant temp behaves as it was designed, steady right in the safe zone.

You are right on the money and I want to repeat two of the things you said:

1. Coolant temp and exhaust temp have very little to do with each other. You can fire up a stone cold engine when it is 20' outside, head up a hill and if there is a problem with your engine (low boost, non-diesel driver , etc. ), EGT's could be 1500 immediately, without the coolant guage even moving for another half a minute (I would not recommend doing that, of course) That is why I would highly recommend to gpuller to install a pyro and boost guage so if you have a boost leak or something, you will see it before you burn up your engine.

2. I would agree that these engines are overbuilt/underused. However, I was taught it is important to maintain proper operating temp to prevent soot build up, etc. even though EGT's would still be high enough. Curious about your thoughts on this.

I guess after what you said about the cold coolant in the radiator, I did some thinking-tell me if I am right. I guess the thermostat is in the coolant flow going to the radiator, so when it gets hot enough to open, it allows cold to flow in from the radiator at the other end. Meanwhile, the sender for coolant temp is somewhere in the block and shows the dropping temp, but the thermostat does not sense this and close until it circulates through the block and arrives later, thus the cycling, which is perfectly normal. Is the reason for the slower warm-up with the updated cummins stat that they allow a small amount of flow all the time and run a lower operating temp, which would keep engine/radiator temps more equal to limit cycling?



Also, for anyone's info: I work at a Case Ih parts department and we carry and can get some cummins part numbersOo.

 

[illflem]

You've got it exactly right.

Seems to me a stat that only allows enough flow to keep things at the correct temp especially when it's cold out would have to be just barely cracked open. I'm not an automotive engineer but know a fair bit about hydraulic and water plumbing - valves cracked barely open to restrict flow wear out fast due a process know as impingement. The metal is actually eroded away.

I know for a fact that when the temp drops below about 10° the stat rarely opens, the heater core is doing all the cooling. I've found that by just speeding and slowing the heater fan or changing from outside air to recirculated air that I can move the temp gauge instantly. When it gets really cold like 20 below any heater position besides recirculate will cause the temp gauge to bottom out and with it goes your heated air. .

 

[bmoeller]

The first winter I had my Dodge, when the first time the temp gauge started its 140-190* swinging, I thought it was a problem w/t-stat (before joining the TDR and finding out it was nomal). I checked the temp. with a meat thermometer, and the temp in the radiator was 140*. The temp on the gauge was 190*.

 

[Texas Diesel]

This is perfect timing, my 12V needs help, used to stay at 180F and it climbs slowly to 150F and wifey is complaining about it. Is P/N 3934373 the one to get? Do I need to specify and new gasket too? My 01 has a rubber sealing ring only, thanks

 

[bmoeller]

The 12v has the 2 rubber seals as the 24v. does. The p/n, I think is the right one for the t-stat. Will have to double check for sure. I have a new one, but haven't gotten it installed yet.

 

[WadePatton]

No, that is the newer one, it doesn't fluctuate as much, but runs cooler. The older one will run warmer with the ups and downs.



My Cummins store only had the old ones--so you could probably find either.



Check out this page for details on t-stat and more:



http://www.dodgeram.org/tech/dsl/maint/2nd_Gen-12v.htm

 

[PTMan]

Hey guys, I've read your posts. My temp fluctuations are such now on my '96 that sometimes the gauge doesn't ever get warm and I get no heat from the heater.

Sometimes it goes up to 190 and stays, other times it goes up and drops unexpectedly to about 140 or so. What d'ya think... will an new t-stat settle it down? I got the Cummins number off one of the last posts.

Is changing it a big operation?

 

[gpuller]

thermostat

Finally got around to putting in my thermostat on Wednesday after work. Piece of cake!

I removed the alt and moved it off to the side, then I cracked the housing bolts and let the coolant run out, so I didn't have to mess with the drain cock.

The rubber was jambed in the stat causing it not to open or close. I thought about cutting off the rubber band but with my luck I figured I'd leave it alone. I reused the existing o-rings, the were in good shape. Dumped in a couple gallons of JD Cool-Guard and I was off.

Driving home afterwords, the temp gauge got up to the 1 on 190 and never moved.

 

[PTMan]

gpuller... Thanks for the step-by-step. As soon as I can pick up a new stat I'll do just that. With 255,000 miles on my '96 I guess it's time! I am assuming you bought the Cummins thermostat. If not please advise. The others seem to be getting better results with it. I have a Cummins p/n 3934373.

 

[gpuller]

PTMan

I did get the stat at the dealer, it was in a Cummins box with a Chrysler p/n decal on it. The p/n was 05014568AA. No cycling as of yet.

I did reuse the o-rings, my motor has 105,000, and they were in great shape.

Good Luck, its a cake walk!

 

[WadePatton]

Sticker shock?



So how much does the mighty DC store get for a t-stat?



Cummins gets $25, which leads me to think DC would get close to $75.

 

[bmoeller]

Got mine from dealer. Was around $30 I think, but don't hold me to it.

 

[WadePatton]

I didn't ask the DC folks. They don't keep anything in stock--no matter the price.

 

[bmoeller]

Been prettty lucky with my local dealer. Have had most of the things I have needed from them. Even had the '95 cooler line in stock, sure surprised me on that.

 

[illflem]

The cooler line with port is used on a gasser AT recall.

I've found most dealers have recall parts in stock.

 

[WadePatton]

oh yeah, DC parts (can't say "Dealer" 'cause I usually hit the "S" on my keyboard instead of the "D"--and some whiners don't like that FWIW) had the throttle cable for my 12v. Recall item.



Of course when my LP was low 16 mos. ago, I got the routine--"never heard of that", "we'll have to diagnose it", "we don't have that in stock". 2 or 3 days out of service estimate.



Of course Cummins sole me one and I was out of service 2 or 3 hours.



HEY, I thought we were on thermostats. Okay I've got a new "old-style" in. Works fine, cycles. Doesn't hang open. I've got a 180 in the 24v, probably go back with the 190.

 

[Deezul1]

I put in one of the "new" style stats from Cummins and it cycled like the old one did so I took it and put in a NAPA stat and 6 mos later I am having to pull the 3rd NAPA stat out as all of them stuck open so I guess its back to the Cummins stat. The NAPA unit has a crummy 30 day warranty which sucks.

 

[SRehberg]

I posted earlier here after installing the latest Cummins thermostat, which still cycled. That was driving around town. I just completed a trip (1000miles) of highway driving, and that stat stayed pretty steady. If it moved, it was VERY little, as I couldn't see it. Just wanted to correct my earlier observation.