1997 5.9L Thermostat

[97OneTon12Valve]

The temperature gauge on my 1997, 5.9L, 3500 with 250K miles, cycles between about 160 and 190 degrees.
I assume I need a new thermostat. I see that Geno's sells a Gates thermo that is rated at 180 degrees. Just wondering if that is a good choice or are there other ones out there that are recommended.
While I'm doing this should I be considering switching out serpentine belt, belt tensioner and water pump? If so, are the units made by Gates a good choice.
Thanks in advance for your advice.
97OneTone12Valve/Madras, Oregon

 

[Chief USA]

I had a similar issue and purchased a Stant 190 degree thermostat from Rock Auto. Keeps the temperature gauge nailed to 190 no matter the outside temperature or how much boost I pull. They are a LOT cheaper than the Cummins thermostat.

 

[GrantP]

The temperature swings are normal until the engine is warm. As far as the water pump and thermostat I'd stick to OEM/Cummins parts, Gates will be fine for the rest. I've been burned before by the belt tensioner pulley so if it's original at 250k I'd replace it.

 

[BigPapa]

I agree with GrantP that it's normal, but not the "until the engine is warm" part.

Mine has been SWANGING (to quote John Anderson) for over 500K miles now, spring, summer, winter, or fall, whether I've driven 100 or 1000 miles without a shutdown.

Drive on.....

-Scott

 

[GAmes]

https://www.cumminsforum.com/forum/94-98-engine/449279-low-fluctuating-coolant-temperature.html

 

[GrantP]

I agree with GrantP that it's normal, but not the "until the engine is warm" part.

Mine has been SWANGING (to quote John Anderson) for over 500K miles now, spring, summer, winter, or fall, whether I've driven 100 or 1000 miles without a shutdown.

Drive on.....

-Scott

My 97 temp always settled down after it was warm, just sharing my experience. But I agree...drive on.

 

[mothertrucker]

I experimented with several different aftermarket T-stats on my '97 3500 & all produced wild fluctuations on the temp gauge.

Finally installed a genuine Cummins T-stat { Cummins part # 3928499 }.
This is the T-stat that Cummins recommended based on the engine serial number.

The Cummins T-stat looks nothing like any aftermarket one I had ever put in the truck.

I have not had any cooling problems or crazy gauge readings since.

If I were you I would contact a Cummins dealer & start off with the correct T-stat that is recommended based on your engine serial number.

 

[97OneTon12Valve]

I had a similar issue and purchased a Stant 190 degree thermostat from Rock Auto. Keeps the temperature gauge nailed to 190 no matter the outside temperature or how much boost I pull. They are a LOT cheaper than the Cummins thermostat.

Thanks Chief

 

[97OneTon12Valve]

I experimented with several different aftermarket T-stats on my '97 3500 & all produced wild fluctuations on the temp gauge.

Finally installed a genuine Cummins T-stat { Cummins part # 3928499 }.
This is the T-stat that Cummins recommended based on the engine serial number.

The Cummins T-stat looks nothing like any aftermarket one I had ever put in the truck.

I have not had any cooling problems or crazy gauge readings since.

If I were you I would contact a Cummins dealer & start off with the correct T-stat that is recommended based on your engine serial number.

Thank You MT

 

[97OneTon12Valve]

The temperature swings are normal until the engine is warm. As far as the water pump and thermostat I'd stick to OEM/Cummins parts, Gates will be fine for the rest. I've been burned before by the belt tensioner pulley so if it's original at 250k I'd replace it.

Thanks for the input GrantP. My T-stat continues to cycle even after warm up

 

[97OneTon12Valve]

I agree with GrantP that it's normal, but not the "until the engine is warm" part.

Mine has been SWANGING (to quote John Anderson) for over 500K miles now, spring, summer, winter, or fall, whether I've driven 100 or 1000 miles without a shutdown.

Drive on.....

-Scott

BigPapa-Thanks for sharing your experiences

 

[97OneTon12Valve]

https://www.cumminsforum.com/forum/94-98-engine/449279-low-fluctuating-coolant-temperature.html

GAmes-Thank you for sending the link regarding fluctuating temps....and thank you for your service!

 

[Cummins12V98]

Cummins T stats are NOT cheap but I would not run anything else. Most are simply little thin pcs of junk.

 

[GAmes]

Over the years I've had to replace my t-stat several times, always Cummins. Some fluctuate more than others, one didn't fluctuate at all. I would rather they do, it tells me the stat is working. I have to look at my records but I believe the one installed now is the one I put in when the engine was rebuilt, 400,000 miles ago.

 

[97OneTon12Valve]

Thanks to all for responding!

 

[Joe Mc]

I'm with the rest as for using Cummins parts, albeit they're more expensive "but" you get what you pay for... IE: replaced T-stat with aftermarket one during a coolant change years back - wild fluctuations. Pulled it out and paid the price for the Cummins one = rock solid @ 190 (once up to operating temp) regardless of load or ambient temps. Water pump (new not reman) from a parts store. Lasted 1 year then started to weep. They gave me replacement (no cost - new not reman) another year and while on the highway started to smell anti-freeze. This time it was spewing coolant onto the (original) alternator... Got another replacement, no cost, when I got home the alternator had went south due to coolant. Went to parts store with pump and alternator in hand, told them I wanted $$$ for pump back (no problem they gave refund) had them check alternator = no friggin good. Told them I wanted new alternator (not reman) at no cost since the POS pump caused the failure. They stood tall and gave replacement "but" I had to give original alt as core. In hindsight I should have rebuilt the original alternator, but hindsight being what it is... Anyhow the Cummins T-Stat and pump have worked flawlessly for well over 7-8 years now. Moral of the post = you get what you pay for so pay once and get the correct OEM (if at all possible) part when it comes to things like this.

 

[97OneTon12Valve]

Buy once pay once-Thank you sir!