Engine/Transmission (1994 - 1998) thermostat question?

[drandle]

Hi,



Is there a updated T-stat for a 1996 12 valve engine. If so, what is the part number.



Thanks

 

[ata]

No there is no updated T-stat for the 12 valve from Cummin's or Dodge. Went through this with Cummin's and Dodge about 3 months ago. Cummin's only makes one T-stat for the 12 valve. they only have an 180 degree and that's it. I bought one from Dodge and one from Cummin's they came in the same box but the Dodge one had a MOPAR label over the Cummin's label. The T-stats in the boxes had the same part numbers on them. And they still have the problem of cycling. Actually I bought two from Cummin's and all three of them cycled. Got my money back on one from Cummin's the other two I got to eat.

 

[CToney]

They did have an undated thermostat that was supposed to cycle "less". It does help but not as much as most of us would like.

 

[Missouri Mule]

The updated t-stat opens more slowly then the oem one. Do a search you should be able to come up with the part no.



But you don't have to change it I'm still on my oem one. The reason it swings is because of the massive radiator.

 

[Joe G.]

When my original t-stat stopped cycling I suspected a problem. Sure enough the rubber gasket had slipped and had the t-stat jammed open. I replaced the t-stat and it's working right again.

 

[ata]

When my original t-stat stopped cycling I suspected a problem. Sure enough the rubber gasket had slipped and had the t-stat jammed open. I replaced the t-stat and it's working right again.

Does this mean it went back to cycling by it's working right again?



My original t-stat did the same thing with the rubber band on it. But it did not cycle. The replacement did not cycle but it got to where it would not let the engine go above 165. I have put three new ones in and they all cycle. So I guess I will have to put up with it. They are to spendy to keep changing until I get a good one.

 

[Joe G.]

The ones that do not cycle have to dampen the open and closing of the t-stat in order to do that. The cycle is caused by so much coolant in the radiator cooling off while the t-stat is closed. Then when the t-stat opens it lets coolant that is a lot cooler than the coolant into the engine so the temp drops. The t-stat closes when that happens and does not open again until the temp is up to the point that causes the t-stat to open. That takes a while since there is so much coolant in the engine. If the temp is not cycling then the t-stat is not working right. It is too slow in functioning or it does not close all the way or has a big leak. People who are used to the small capacity of a car engine get all upset at the cycling. I prefer that when my t-stat opens it opens all the way. No fooling around. If it's restricting flow or not closing all the way, then when you really need the thing to work right like in summer towing you may have problems. So if my t-stat stops cycling I know that something is wrong and it needs attention. It's only cycling 35° to 45° anyway so what is the big deal? EGT swings a lot more than that just going over a hill so we know that the iron in the head near the pistons is cycling a lot more than 45° just running around town or down the highway. If the cycling is such a big hairy deal that a lot of money has to be spent to fix it then why does Cummins say that the cycling is normal? They have a vested interest in engines lasting a long time.

 

[ata]

Joe, I understand what is happening with the three new t-stat's that I have put in. But I can't figure out why I had two that went over 100000 miles that didn't cycle and the gauge sat right at 180 190 all the time (summer-winter) and when they failed they ran cold and now I can't get one that will hold still for more then 2 minutes. Oh well like I said before I'll live with it.

 

[Joe G.]

I think what has been happening is that there have been attempts to make a t-stat that won't cycle to please people who get upset about it. I really don't trust them for the reasons I said in the above post. I drove about 300 miles from here to my daughter's house in Roseburg with the temp gauge steady all the way. The next day I took it apart and found the gasket had shifted. If the one I have now stops cycling I will do the same thing.

 

[MBNicholson]

Thermostat Problem?

I have a 1996 3500 with the 5. 9, 127,000 miles. Our outdoor temps range now from around a low of 32 to a high of 43. Recently, my temp gauge has showed a normal warmup, but when I get on the highway, around 55, the temp slowly climbs up to @ 210 and then cools right down like the fan kicked in (but it hasn't). Then it climbs right back up and does the same thing. We (my local shop) replaced the thermostat, then the sending unit, and then a pressure check for possible head gasket problem, all with no problem or change. There is evidently no engine temp parameter for the scanner to read, but temp gun reading before and after the thermostat indicate pretty much the same at idle. This gauge has always indicated very cool temps and this up and down is driving me crazy. I can imagine how crazy I'll be this smummer hauling our 35' 5th wheel to CO. Could this just be this cycle problem you are talking about? Thanks for any advise.

 

[Joe G.]

Read my posts above. The cycle is normal. Don't let it bother you.

 

[MBNicholson]

Thermostat cycling

Joe G - it appears you have made my day! I guess I'm just fussy with my truck. I bought it new and just fix anything that goes wrong with it. It works great and I love it. You know, the original thermostat never did this! The temp gauge has always, until recently, been rock solid. The only time it went up was three years ago when I had to replace the fan clutch. I guess the original just gave up. Is there two part numbers now, one for the old and one for the new that allegedly doesn't flex as much? I really appreciate your help, Mike N.

 

[Joe G.]

Mine cycled from when I bought the truck new. The cycling was causing so much concern, Cummins may have used a different one in'96. When the rubber cover on mine failed it was a Sunday in Roseburg, OR where our daughter and son-in-law live. I got one at NAPA just to get me home. It worked fine so I left it in. It has about 150K miles on it now and is still working fine. The temp gauge says 190 when the t-stat opens and about 150 when the temp starts back up.

 

[DPashko]

if you want to minimize cycling put in a dodge 440 t-stat. they come in 160, 180 and 195. I have a 195 in mine and first cycle is about a 10-12* drop then after that its about a 3 to 5* swing.

 

[BigEasy]

Pashko, do you have a part # for that? I would love at 195* t'stat... I have had the rad completely blocked with cardboard all winter and can't get any good heat.

 

[DPashko]

Sorry I threw my box out... I got mine from napa, just ask for a 1971 charger/ road runner/ cuda / challenger whatever your dream is . . hahhaha... 440 t-stat 195* and they will give you the goods! I think it was $12... i have replaced two of them nice cummins ones within a year myself. . that lovely rubber ring comes off the t-stat and holds the t-stat open... not worth the 60 bucks thats for sure. And i had gotten the supposedly slow opening one and it still goes from 180* to 160* cycling. Dodge 440 has been working flawless so far. And it works in my road runner too!

 

[BigPapa]

I'm with Joe G. on this one. My original thermostat is still swinging with over 320K miles on it. Swings from @ 150 to 190 constantly. If it didn't, like Joe, I'd get worried.



Scott

 

[RHestand]

BigEasy,

NAPA 195* stat. #532090.

Ray

 

[Shadrach]

For those interested the Cummins p/n for the std stat is 3928499 and the "slow cycling" one is 3934373. both are 180*F. You will also need 1 of each of the seals 3925466 and 3927305. Shadrach

 

[BigEasy]

BigEasy,

NAPA 195* stat. #532090.

Ray

Thanks a bunch... I love this board!