Engine/Transmission (1994 - 1998) Thermostat help

[gpuller]

I need advise, I have a 98 12V that needs a thermostat. I checked every parts store in my area and no one had it in stock or said it was the same as a 360 gasser?!?

Finally found one, Stant p/n 14248. Is this correct? I'm a lot unsure. Also got the big seal, but is there another seal? Are they reuseable?

I have searched past posts but only became confused. Which stat to use? Should I use the Stant or get one from the dealer? The way it sounds I should also have a drain cock handy. Maybe I should just get the stat form the dealer as long as I'm there? I really dont want the Stant to stick like others have had troubles with.

Anything you guys can add?

 

[Grayhackle]

I had problems with a 1990 12v thermostat. I replaced the thermostat with a stant from Checker Auto. The temperature would swing from lo normal to high normal on the gauge. Took it back and exchanged it and it did the same thing. Finally , I got my money back and went to Cummins in Salt Lake City. It worked ok, but not near as good as the OEM themostat as it had a wide swing too. I lived with it, but was not happy. Replacing the darn thing was beginning to wear me out! I have never seen temperature swing like that on any other vehicle. When the air conditioner was on, it looked like the engine was running on the hot side and then swing clear back down to low normal and then back up again to where you thought it was heating up. Got me hypmotized running down the road staring at the temp gauge!! Hope you have better luck with yours, you would think that making a thermostat would be an exact science by now!!

 

[JNailor]

I replaced my t-stat when the truck was 6 months old because it stuck open when I pulled my trailer. Back then (in 95) I had to get it at the dealer. Its not the same as a gas 360. If memory serves me, it is a two valve unit which blockes the bypass when it opens.

Dana



BTW- Mine never swings. It just rises to operating temp and holds steady.

 

[SRehberg]

I just finished changing out my thermostat due to it was held open by the rubber sleeve that had let go. I replaced it with a Cummins, latest, greatest etc. Now instead of swinging from just above 140* to 190*, it swings from just above 140* to 180*approx. Other than the rubber jammed in the thermostat, it could have been reused. There are two gaskets to replace when you change it out, separate purchases. The ones I took out looked like they could be reused, but I opted for new. Illflem was the one who helped me with the first go around diagnosis.



The petcock didn't give me any trouble, so it still has the same "O" ring as before.

 

[vssman]

I had nothing but trouble with the stant t-stat. I even called stant engineering and was told it is a different design - Theirs needs some pressure and temp to open thus the high reading before it opens the first time. Cummins uses a temp only design and opens without any need for some pressure. Hence the difference in appearance: stant - witches cap style, cummins - top hat style.

 

[rjones]

I work at a auto parts store and everything I tried sucked ended up getting right from cummins and it worked fine if you get the updated stat not the old one that keeps cycling all the time.....

 

[schlite60]

Themo Part number

What is the Cummins part number of the updated Themo Mine is running wide open again It also might be the gasket moved

 

[rjones]

Re: Themo Part number

Originally posted by schlite60

What is the Cummins part number of the updated Themo Mine is running wide open again It also might be the gasket moved

I believe its #3928499

 

[SRehberg]

The part number that is quoted here is exactly the one I installed. Either mine is defective or something, as it still cycles.

According to Cummins when I bought it, this was the latest design, so possibly I am the only one experiencing the annoying cycling.

 

[DMC]

The temp on my 12 valve flutuates a good bit until the motor is warmed up. From about 185-160, since I put in a T - Stat from Napa. Before when I was running the original T- Stat it got to where it took a long time to warm up and would only go up to 180 on a hard pull.



I have seen T-Stats with a little bleed hole, about 3/32 in diameter near the center of some of the old 172* GM T-Stats and was told that this design would delay the opening of the T- Stat due to cooler water passing thru the hole. Thus keeping the T-Stat closed until the water in the motor had time to build heat.



It takes my motor at least 10 miles of running to stabilize some what. And at least 30 to completely stop fluctuating.



Good Luck



Don

 

[Loren]

It was well known when the 12-valves were still being sold that the temperature on the gauge would fluctuate. Mine would climb slowly to 190, then drop rapidly to about 140, then repeat. This was normal.



I've never changed my thermostat, and the temperature gauge still behaves the same way after eight years. I'm happy with it.



If it's not broke, don't fix it.



Loren

 

[WadePatton]

Dip test.

Whoever said that pulling the t-stat on a 12v is a breeze never pulled one on a 24v--now that's a BREEZE.



Anyhoo, I got the little b#$^%# out. It was doing the normal fluctuation sometimes and then other times not heating up at all. Whenever I have cooling system issues NOW I always start at the thermostat (don't ask).



The dip test is what I call testing the stat with two pans of water. One pan is boiling the other is room temp. Simply hang it on a wire and dip it into the boiling water (212F at sea level--less with elevation). It should open fully. Then dip it in the cold water and it should close.



The first time I did this I found a stat that was only partially opening. When I performed the test on my 12v stat, it opened partially and then would NOT close. It finally closed overnight. In both cases the stats were clearly faulty.



It helps to have a new stat on hand for comparison--and making sure that it's good from the gitgo.



Got new stat from Cummins today for $25 and will try it out when I put the truck back together. Somehow the radiator came out and then the fan and balancer and timing cover--now I have a dowel to tab and pump to advance.



EDIT: Look what I found on dodgeram--

A series of revised part numbers has been issued - check with a Cummins parts department for the latest.

P/N 3934373 eliminates temperature fluctuation but engine warmup is slower and the operating temperature is lower than with previous t-stats.

 

[SRadke]

Yep Wade, that's the part number right there. I put one of those in my 96 and it stopped the fluctuating. It never got above 165°, but it didn't fluctuate.



-Scott

 

[illflem]

Originally posted by Loren

It was well known when the 12-valves were still being sold that the temperature on the gauge would fluctuate. Mine would climb slowly to 190, then drop rapidly to about 140, then repeat. This was normal.



I've never changed my thermostat, and the temperature gauge still behaves the same way after eight years. I'm happy with it.



If it's not broke, don't fix it.



Loren

Best advice right there.



Even though the gauge is swinging around the block temp is very stable.

Folks that have an oil temp gauge will attest to the fact that it holds steady.

If my coolant temp ever stops swinging around then I'll fix it.

 

[akline]

Isn't it better to make sure a diesel is running hot enough to run clean? (up to a limit) I like the idea of stopping that stupid fluctuating, but I would rather see mine run a solid 180'

 

[WadePatton]

My Cummins store didn't have the new one, but had three of the old ones. I'm glad I got the old one now, because my stat wasn't opening fully AND I like the higher operating temp. How they say "happy accident". I didn't know about the difference until after I got the replacement.

Originally posted by SRadke

Yep Wade, that's the part number right there. I put one of those in my 96 and it stopped the fluctuating. It never got above 165°, but it didn't fluctuate.



-Scott

 

[illflem]

Originally posted by akline

Isn't it better to make sure a diesel is running hot enough to run clean? (up to a limit) I like the idea of stopping that stupid fluctuating, but I would rather see mine run a solid 180'

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.

 

[gpuller]

Thermostat

Well, I went to the dealer and bought the Cummins stat. P/N on the box is 05014568AA and the box is dated 7/26/03.

I never really had much cycling with my old stat. When pulling my tractor and trailer, (approx 20,000lbs combined), in the summer the temp just hangs around 185-190. I really should have EGT and trans temp gauges but then I'll only know how hot things are. Run it!

Still have not gotten around to installing thermostat. Can't get the truck away form my wife long enough to get it changed! I've got to get it done soon, the 50 degree weather can't last long.

Do I need gaskets or are they O-rings that can be reused?

Thanks for everybody's input.

 

[vssman]

I reused my o-ring - The dealer didn't have a new one when I bought the t-stat.

 

[SRehberg]

I recently changed mine, and there are two rubber rings in there. Both came out in good shape, but had already purchased the new ones, so I installed them. The others would have been just fine, they were in good shape and pliable. One is a square type "O" ring and the other has a "stepped"shoulder on it. Easy change out.