Thermostat swing

[Dfeland]

Is there a thermostat that is made that does not have such a large swing to it. In other words I can watch my engine go a little past the fitst bar on the temp guage and then it will drop to the midway point between the c and the fist bar when the thermostat opens. Is there one that is more of a constant??

 

[barryg41]

T-stat swing

We had this discussion last night in the 12v forum.



Bill Fleming wrote me back:



Barry, the cycling problem isn't the t-stat, it's the overbuilt cooling system on our trucks. Seems like it was designed to pull a freight train in 100° weather. I've often thought that during cold weather that you could even remove the radiator and just the heater core would be enough to keep things cool.



Some have had luck with new t-stat, but in my borthers 96, it didnt work out. It stills swing like the OEM did.



Hope this helps!

 

[Gary - K7GLD]

AFTERMARKET thermostats are NOTORIOUS for what you describe - I had the same problem when upgrading my radiator (see sig), and also replaced my thermostat with a name brand one from local auto parts. It wandered up and down the scale radically, and did so for about a week - until I finally went direct to a Cummins shop and bought the RIGHT one from them - seems the "jiggle pins" in the Cummins T'stats are of a much different design than the commonly available "replacements", and the replacements don't function properly due to trapped vapors behind the T'stat that prevent proper operation. I notice that later Cummins T'stat housings now have included a small-diameter fitting and hose that apparently bypass the thermostat - presumably to avoid the rather common problem by allowing a small stream of vapor/coolent to circulate past the T'stat itself, eliminating the trapped vapors...

 

[Pit Bull]

I have a 24 valve 2000 truck and my thermostat goes up too a little above halfway (190) and then drops just below 190 then alittle above 190, etc. Is this what you are seeing? Do the 12 valve first generations have a bigger swing then this?

 

[barryg41]

My truck did the swing thing also for about the first year. Then it got worst when I was towing. The temps would swing up to 205-210 back down to 180. I put an DC t-stat and fixed the problem. I read here on TDR that the 99's had some t-stat's come bad from the factory.



Big Toy:



My brothers truck (96' 3500) swings from 170 to 190. Does it even when towing.

 

[Power Wagon]

My truck swings radically... when you first start off, it takes perhaps 10 to 15 miles of very slow climb all the way past the top of the "normal", and then it suddenly falls to below the bottom "normal" range, and after that it swings back and forth all the way across from above to below the "normal" range.



I have a new thermostat to put in it as soon as I get a chance.



I have experienced this in other vehicles... My car when through 4 or 5 thermostats in less than 2 years, one lasting less than a month, for this problem. When I finally got a good one last summer, it's been fine ever since. The parts house replaced all but the first for warranty. In every case, it was possible to see some place on the thermostat itself, where something had been sticking / rubbing.



Even on the Power Wagon, which has had fresh water and antifreeze each year since I got it, thermostats have not lasted even a full year. I replace them after a few months use because I see that they no longer maintain control. Either overheat or have huge temp swings with outside conditions, due to failure to close and/ or open all the way. I think it's cheap parts. I've tried Napa's best, carquest's and name brands like Stant, to no better results over the last 5 or 6 years. Previous to that, I don't recall buying thermostats as often as I bought tires for the car - several years apart.



The CarQuest premium one I bought for the Cummins was only a few dollars. I can't help but think I'd gladly pay double (what's 20 bucks???) for a GOOD thermostat that does it's job reliably - although this one does look pretty well-made.

 

[dan_gilson]

The Thermo in my '96 12V went from 190 down to 140 and then back up to 190 every two minutes when unloaded in cool (50F) weather.



I am glad to hear that Cummins finally fixed this. At the time 2 dealers told me that this was normal and I just had to live with it. I am sorry but I just did not buy it. I called Cummins and they told me the truth. The dealer looked kind of funny after I had caught him in a lie. The bigger issues was that they did not have a solution at the time. This issue, after many others, finally caused me to sell my '96.

 

[DieselBuzz]

Earlier this winter I took a 240 mile trip and mine was swinging. I literally stopped for one donut and asked that it be put in a doz. box(shouda seen the girl's face). Ate the donut and slid the box(unfolded) in front of my radiator. This stopped the swing for the most part. My guess is that our radiator is so big that even with the thermostat closed that coolant is chilled a lot. So much so, that it shocks the system when it opens. The thermostat reacts and closes quickly. Then it cycles again. There is less of a need for cooling, so I try to make my system meet a smaller need. I would be willing to try donut boxes, winter grill covers, removing the fan before blaming the thermostat (IMO).

Art

 

[dan_gilson]

What Cummins told me was what you figured out for yourself. The raditor that is in the 12V is the same as the V10. It is designed for 400+ HP. It is good news for the BOMB'er! Bad news for the thermostat. It causes a pretty bad control system oscillation (?sp). Cummins is supposed to have a new thermostat that is supposed to correct this. I would go directly to Cummins. I have yet to get good information from a dealer.

 

[Dscholz]

I noticed that my thermostat started cylcling like that in colder weather. I didn't think it was a big deal since I just converted my '90 radiator to the '93 radiator. It worked great for about a month and a half. The only problem is that I loaned my truck to a friend Saturday to tow a car and trailer up to Fremont. He was about 10 miles from his destination when a young girl driving a little green honda decided to pass him and ran into the center median. After she bounced off the median and my truck, three times each, they came to a rest after my truck slid sideways and encountered the K-Rail with my front bumper. Trailer was fine, car on trailer was fine, my truck is not. Sorry for the long post but I needed to vent.

The truck is not believed to be totaled and it's at a body shop, but my new radiator was punctured. Guess I don't need to worry about the thermostat right now. I just want my truck back.

Dan

 

[dan_gilson]

Here is my take on the temperature swing...



I just can not be good to the engine. I am an engineer by trade. Although I work on computers for a living, I had to go through all the material science classes for a EE.



A repeative 40-50F temperature swing in a short duration on a lot of cast iron can cause a lot of problems. Seals and warpage are a few that comes to my mind. Running under temp will cause more air pollution and reduce fuel economy.



So, I did not buy for a minute that this is normal.



For that cost of a new thermostat that corrects this it sounds like it is worth it.

 

[Jet Tech]

Proof of overbuilt cooling system... ... Drive your truck then stop and feel the cold side tank of the radiator. I was amazed how cold it really was.

 

[Gary - K7GLD]

My dad used oversize radiators in his trucks in the hauling business for years, I have had a couple of my own - and let me tell ya, it is NOT normal for radical constant temperature swings in varying seasonal climates, PERIOD!



As pointed out above, those types of temperature variations are BAD for engines, and no manufacturer will knowingly build a cooling system that places those additional temperature stresses upon the engine... Now, yer local service department might shine ya on with the notion it's "normal" - but THOSE are the same guys tellin' ya yer front rotors are SUPPOSED to warp every 10,000 miles, and front pads are SUPPOSED to wear out every 15,000 miles...



IF yer temp guage is revealing a constant swing pf more than 5 degrees or so, summer OR winter, you have a PROBLEM! Naturally, towing a heavy load up a long steep grade WILL create a change in temperature, but that's different...

 

[RDusch]

The new stats from the dealer straightend mine temp out, the original stat would run 140 on the cool side and 180 on the warm side, not a fast change but it would change.



I installed a NAPA stat, that thing would jump like crazy 170-200 real fast. I ordered a stat from the dealer, this one will run 170 unloaded 180 loaded, but no drastic changes.



The differance is the napa stat is a bi metal unit that clicks open then closed, not good, the Chrysler stats have a wax filled element that modulate open slowly if it only needs to be open 50% to maintain a constant temp thats all it does, they work great, and are the recomended stat for these trucks, they heat up and cool down to fast for the bi metal elements... ..... RD