Engine/Transmission (1994 - 1998) Napa thermostat

[firemanmarc]

Hello. I put a Napa thermostat in my truck last weekend, and it seems to have a mind of it's own. Opens all over the temp gauge. . Are these known to go bad fast?? Thank you, Marc

 

[Joe G.]

I put one in my truck several months ago. So far so good.

 

[WDixon27]

that's generally considered normal for these trucks, i drilled a hole in my new cummins sourced t-stat so hot coolant could circulate around the element and keep it from getting shocked so badly by the temp changes and that all but stopped the cycling, the hole location changes depending on the design of the t-stat but about a 1/16-1/8" hole so coolant can get right at the wax element (do not drill into the element!!!) should help stabilize the temps (at least it did with my truck)

 

[Joe G.]

The cycling is NOT a problem. It is normal. I really really doubt that there is any temperature shock for a 40° coolant temperature change. Consider the changes in temp close to the combustion chambers when going over a hill towing. 40° is nothing. The net result of dampening the cycling is to make the engine run cooler. Then your heater doesn't get as warm so you shiver.

 

[DKayser]

Napa T-Stat

Used one on my 95. My only complaint was the 180 degree instead of the 195 . Semmed to cycle less,but slower to run you out of the cab. Absolutely would not go over 190 , even with the Prowler hooked on & pulling a hill. Best part was the $ difference between them & Mopar. DK.

 

[firemanmarc]

The thing is I understand the cycling. It drops down the way I know they should when it actually opens. Sometimes it won't open til way after 190, another time it gets close to 200 before it opens, and still other times it takes forever to get to 190 and then it just sits there like it is not opening. Guess I am going to pull it out and change it again... . Thanks, Marc

 

[WDixon27]

mine still runs right in the middle it just doesn't drop to 140-150 every minute and a half, the way i see it the t-stat is now regulating temp like nearly every other engine on the road instead of getting to temp, slamming open then getting hit with the cool coolant and slamming shut making the temp gauge do a impression of the volt meter when the grids cycle

 

[Nate]

When I was in Alaska, we had about 12 Dodge Ram trucks, ranging from 96 to 01 and ALL of them did the temp swing thing. They would hit 190* while going down the street at WOT (7. 17 gears and governed to ~35-40mph) and then the temp would fall down, go back up, down... keep on doing that.

 

[Joe G.]

mine still runs right in the middle it just doesn't drop to 140-150 every minute and a half, the way i see it the t-stat is now regulating temp like nearly every other engine on the road instead of getting to temp, slamming open then getting hit with the cool coolant and slamming shut making the temp gauge do a impression of the volt meter when the grids cycle

These things are not some gasser with a barely adequate cooling system. I sincerely doubt that there is any slamming going on.

 

[RustyJC]

Well, my 24V with the original Cummins 190 degF thermostat runs a steady needle-width below the 190 mark when running empty and a needle-width above the 190 mark when towing. No swings here.



Rusty

 

[24valver]

my napa t-stat will open at 220 then go down to 150. then it will cycle back an forth between 200 and 160. im putting a cummins t-stat in over the weekend to see if its any better.

 

[Gary - K7GLD]

I had swapped the OEM T-stat in my old '91 once purely out of habit as one of the things that "needs" to be done periodically - and bought a NAPA one to replace it. That dern thing would wildly cycle from high to low constantly, and never would settle down. I quickly made a trip to Cummins West in Sacramento, got a proper stat, and my problems were over!



I don't care what anyone sez - when the OEM stat, and the Cummins spec'd part DON'T cycle wildly - and a NAPA one DOES, something just isn't right, and while it might NOT damage the engine over the long haul, I sure can't see any way it's GOOD for it!

 

[Nate]

So explain why 12 truck with factory T Stats would all do it?





My truck doesn't do it, but I think the T Stat is bad. Normally runs around 160* or so. I picked one up yesterday from Cummins. Was just over $30 with tax.

 

[Joe G.]

Later t-stats were changed to be more steady in response to all the complaints. I think that the only way that it could be more steady is to either open slowly or leak. Neither of those options are attractive to me. Mine has always cycled from the day I got the truck new. When the original stopped cycling I knew something was wrong. Sure enough, the rubber around it had slipped and jammed it open. No Cummins store was near where I was when that happened so I put a NAPA stat in with the intention of changing it when and if it caused problems. That has been some months ago. It is cycleing properly again. So far so good.

 

[Vaughn MacKenzie]

I just flushed and changed the coolant on my '98 12v and since I did it "spur of the moment" I just bought some cheap T-stat from Schuck's and put it in. So far so good, stays steady around 170F (180 stat) and doesn't cycle at all.



My '96 always cycles some but not that bad. Usually 160-180. Cummins changed the T-stat design & orientation on the 24v so that's why it's not much of an issue on newer engines.



Vaughn

 

[WDimig]

funny i find this thread, cuase i dont know what the heck is going on with my NAPA t-stat. it does what everyon else say it has done, they first time it cycles, with will be around almost 200-205 deg. ! i almost shut the truck off the first time i saw it, it scared me a bit, i didnt think it was going to cycle, once it cycles the first time, it will goo alll the way down to about 150, then it will go back up to 190 deg. and if i get on it really hard it will go over to almot 200 deg. which i dont like, cause im not even loaded, and i had never had those high temps before. im going to get a new tstat from work on monday, just dont know if i should go with the revised 180 tstat, or the 195 that fluctuates. i never have a problem with the truck warming up, i just dont like the temps that the engine is running at. any thoughts on this subject gentlemen??



wes

 

[JGrover]

My 97 has always gone from like 180 down to the warm line.

If im pulling my 9k boat in 100+ degree weather up some really steep long grades. The stat will sit on 180

When my fuel heater started sucking air. I wasnt getting full fuel and boost at 1900/2000rpm I actually had to drop to 4th pulling the big hills :{ 2300rpm That brang my engine temps up around 200

 

[JDLight]

Make sure that the T-stat is installed in the correct direction. I know this sounds crazy but I had a head gasket done on mine a while back and had the t-stat changed while it was apart. It was terrible when I got it back. It always had some swing but nothing like this. I took it apart and found that the mechanic had installed it backwards with the end that is supposed to go toward the head toward the radiator. It would fall down on 140 going down the interstate, then back up to 190 when around town, but not consistant the gauge was all over the place. I put the updated cummins t-stat back in it. It still swings slow 160 to 180.

 

[snake]

I put one in my truck about 4 months ago. So far so good.

 

[JWaters]

I love my temps moving up and down, I know it is cooling and has enough reserve incase I pull a long hill. I will not change to a stat that stops that from happening!