New Stat Blues

[RHARVEY]

I just installed a new thermostat and it is acting strange. When the stat opens, the temp guage drops down to 140 and then it climbs back to its normal spot. I slow down for a stop sign and it drops to 140-150 and then it climbs back to normal again. When I pulled back in the drive it stayed steady. .
Is it a bad stat?

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[Missouri Mule]

Rick,
Seems you were sold the old one not the updated version. #ad

Honestly you could have a bad Thermostat.
Your fan isn't going full out is it?

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Bill Thomas
Missouri Mule - 96 Wht 4X4 ST CC,5 spd, 3. 54, 8 ft bed, 1 ft high cheater boards.
99 Freightliner bl/wht FL60 ISB-5. 9 24v,215 hp,520 tq,6 spd, 3. 59 nsr,16 ft box, 19. 5 tires,Wt/gvw 11,000/23000

 

[RHARVEY]

I didn't notice any difference in the way the truck runs. I was surprise that Cummins would sell me the old model instead of the updated one. The one that I pulled out must have the new one because it worked great. I may put the old one back in and not worry about it right now. Is it going to hurt anything with the current one that I have in it(new one), until I get a replacement from the Cummins shop? One thing that I noticed about the new one is that it did not have a rubber coating around the spring section on the outside like the old one.

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

[This message has been edited by RHARVEY (edited 03-31-2001). ]

 

[HEMI®Dart]

Rick,

If the Cummins shop gave you a T-stat without the rubber sealing surface, its probably for a pre-'94 Dodge Cummins. Its not even remotely close. I had the same trouble with my local Cummins dealer

You want Cummins Part # 3934373

Except nothing else.

Even if he has to order it. Parts guys told me that this Part # was no good. A call to the Cummins Customer service and they said thats BS. Its a good part #. He sent me a 3934373 T-stat N/C. #ad


This is the updated & revised T-stat. Its not supposed to cycle like the old ones, or the one you got, but mine still did.

I have finally solved the cycling problem. I took off the engine fan & blocked the radiator with cardboard. No more cycling. Too bad its only a winter solution. #ad





[This message has been edited by HEMI®Dart (edited 04-01-2001). ]

 

[RHARVEY]

After I double checked the anti-freeze and added about a cup(which would not make that big of a difference), I decided not to put the old stat back in until I got more info. On Sunday we drove around for a while and the stat never again did move once it got opened. I noticed this morning on the way to work it stayed solid all the way. But I did notice that it is lower than the old one. It hold about 180* instead of 185 or so. i will call Cummins today to make sure that I did get the right one. I am still not sure that the stat that I got was the correct one.

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[RHARVEY]

I just got off the phone with the Cummins shop,and they said that infact I did have the 'old style' stat. What happened when the counter person looked up the number of the stat, they did not have it in stock so they backed up one number, which was the old one.
I gave them the number that HEMI®Dart gave me and sure enough they had one on the shelf and they are dropping it in the mail today. And are including a new set of gaskets. .
Thanks for all the responses and a great big thanks to HEMI®Dart for including the numbers. I think it surprised the parts guy! I would have been scratching my head for a long time trying to figure this out, but thanks to the members, it will be fixed quick.

Thanks
Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

[This message has been edited by RHARVEY (edited 04-03-2001). ]

 

[stick]

HEMI:
I just received a new thermostate from Cummins Southwest with part number 3928499 which is the same part number as the original thermostate.
I had to have it shipped to me because i don't live close to the shop.
I was a little disappointed when I received it because i thought i would get the updated thermo. But i had to put it in anyway. I have watched the gauge all week and it goes to about 180 and stays right there, up hill or down. I have'nt pulled a load with it yet, but maybe they fixed the old thermostate also?

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97 2500 4x4 5spd. TST/605. Exhaust Brake. Amsoil Dual Remote.

 

[HEMI®Dart]

yep Stick,

Thats the old one. I still have one of those unused on the shelf. Even the new one thats not supposed to cycle still does. Or it tends to run cooler, but stay steady. Too cool in my opionin. I'd rather have the "cycler".

 

[Champane Flight]

I've found that my thermostat holds steady between 160-185 if I'm pulling a load. If I'm running empty it cycles between 140-180. I have another spare just in case. It did stick when the truck was newer,but it stuck open and the engine wouldn't even heat at all. I just tapped the housing and its been OK ever since.

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95 Dodge 2500 Luverne grill guard,headache rack,running boards and Amzoiled. Soon to be mildly bombed. 84 Dodge d-150, 318 Hooker headers,Edelbrok intake,mallory ignition,Carter Afb,Accel coil,and Custom dual exhaust. Boat,fifthwheel,motorcycles,and shop. 72000 as of 3/1/01,not even broke in yet. Old Dodge 126000 miles and running better than new.

 

[stick]

HEMI:
All i know, is this one ain't cycleing !!!

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97 2500 4x4 5spd. TST/605. Exhaust Brake. Amsoil Dual Remote.

 

[RHARVEY]

I just installed the new version this past Saturday, and it cycles worse than the first one that Cummins sold me. I will putting the old one back in. When I took it out it worked great, it would hold 180* at normal driving and when pulling up hills in the heat of the summer it would climb to 190 and then drop off when I crested the top of the hill. What is up with these thermostats. . I believe they are a PITA>>>if you know what I mean. .

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[Swamp Donkey]

I am changing my engine coolant tommorow and was going to get a new thermostat, but I think I will save myself some hassles and keep the original one in there. Don't have any problems with engine temps so why mess with a good thing! Unless someone convinces me why a $45 dollar thermostat is really needed when this one seems fine.

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John McEachern
Fort St John B. C. Canada
1998 12v, 4X4, QC, auto w/tc switch, air, tilt, cruise, 3. 55 gears, TST #6, Isspro boost/pyro/transmission gauges, BD VB&TC, CC industries headache rack and rails, JVC KD-SX949 Cd player, forest green, Brigestone Dueler M/T's 285/75/16, Eagle 16x8 rims, K&N airfilter.

 

[RHARVEY]

I still have the 2nd stat in the motor, but I also have the old one in a zip lock bag in the tool box just incase I need to change it. The first day that I changed to the 2nd one, it cycled worse than the 1st new one that I put in. I have driven about 50 miles and this ones seems to have settled down alot. I want to watch it until the weekend to see if it stops the cycling. If it don't, I will re install the old one and put this new one in the tool box.
If it were to do all over again, I would have left the old one in and forgot about it. .

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[RHARVEY]

I called my local Dodge dealer and talked to the diesel mech to get more information on the way the stat was cycling. And the information that I got from he was that it could be air in the system that could cause some of the problem, but also according to his books, the stat is suppose to cycle! He said that the book states that the guage would rise to where the stat opens and then it would drop to sometimes as low as 150*. According to his understanding and the way the book reads, this would show a healthy stat. But this all seems strange to me. What I did last night was to try and get all the air out of the system to see if that makes a difference, and this morning the guage was solid on the way to work. We'll see!!!!

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[Joe G.]

Rick,

This is a real "don't fix it if ain't broke" thing. The cycling stat is NOT a problem. It just looks odd. I wonder if fixing it is the thing to do anyway. Maybe the steady stats don't open as wide in order to maintain the steady state condition. If that's the case then the stock one would allow more coolant on an long hot pull. It's the flow of coolant into the engine when the stat opens that causes the temp drop. The only way that I can imagine to dampen that is to restrict the flow. These things have a lot of coolant so I'm not surprised that there is quite a bit of difference in temp between the block and the radiator. I've got over 163K on mine and it still has the original stat which cycles just fine. This time of the year I see it cycle from about 150 to 180. That's only a 30 degree change in coolant temp. I doubt that the iron is changeing that much. I have a hard time thinking that the cycling I'm seeing is a problem.

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Joe George
Eureka, CA

'95 2500 CC auto 4X4,3. 54,Combo EGT/boost guage,custom switch panel,PacBrake,TST #5,DTT TC/VB,Automatic motorhome steps on both sides,Foldacover hard bed cover,Cummins chrome kit,Black steel grill guard,Front hitch receiver

 

[RHARVEY]

Hi Joe,
What your saying is exactly what the Dodge Mech. said. When I ask him about how steady my old one was, he thought that the old one may have had a sticky spot and not letting it cycle like it should. It sure looks strange when the needle moves like that when the other vehicles that I have driven holds steady on the opening temp of the stat. But of what Gerry(Dodge Mech. ) says that this thing cycling is a normal occurance. And this stat does go from 180 down to 150 and then back to 180 over a period of time. But I also have the old one in the tool box if I need it on the road. .

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[RHARVEY]

OK one more time around the thermostat tree again please... I spent about 30 minutes with Cummins Customer Service(Ind. ) concerning the problem with my new thermostat that Dodge says will cycle and thats the way there books says it should do.
After Customer Service(Daemon) picked himself off the floor from laughing, he said that in no certain terms was the stats suppose to cycle like that.
Hemi Dart. . I gave him the number that you supplied to me(thank you)he said that he had one of those on his desk, and they also have a serious problem of cycling and they are not any good!
Stick. . I gave him the number that you supplied and he said Yes, that is the latest stat that was re-designed and they have had great results with it. To his knowledge he don't know of any that has given them problems.
When I got off the phone with Cummins, I called my local Cummins shop where I got the first 2 stats and explained what I had found out. To make a long story short, they are sending me a new stat'Part # 3928499' at no change and also a gallon of 50/50 mix coolant.
I also found out that the information that I got from Dodge was not exactly true!
It looks like I get to install another stat before my trip!

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

 

[RHARVEY]

I installed the new thermostat that Cummins says will stop the cycling(part #3928499) night before last. On the way to work yesterday the guage came up to 185 or so and then dropped off back to 150 and I thought here we go again, but it climbed to about 175 and it stayed! On the way home last night it did the same thing and also this morning. Once it opens and drops off and then climbs back up, it locks and stays!!! I think this time they(Cummins) got it fixed. .
Now if I can get my fuel sending unit to work!!!!!!!

Rick

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RICK
97 2500,CC,5 SPEED, 3. 54 Limited Slip,Psychotty System,K&N, Pre-Turbo ISSPRO 3" Pyrometer & Boost Guage,Silencer Ring Removed
15,000 RBW 5th Wheel Hitch,25' Excel 5th Wheel,Rancho RSX17000 Shocks,Amsoil Dealer,Straight Piped

[This message has been edited by RHARVEY (edited 04-25-2001). ]

 

[Cooker]

What to do?



I'll be changing my coolant this week and planned on installing a new stat as well. Cummins sold me #3928499, and as I read this is the old part number. Maybe after having the stats in for a little while longer someone can offer some more info. Should I put this one in or get the new "revised" stat?



Thanks,

Ryan

 

[RHARVEY]

COOKER,

Since I installed the 3928499 part number, I have not had any problems with the stat cycling. I have put over 5000 miles on it and not a problem.



Rick