1996 12 valve thermostat question

[Solar1]

Hello folks, The last couple winters i noticed lower engine temp (more than usual). Even in the summer the temp was low unless Im running 70mph or loading the engine a bit.

Now I know that diesels run cooler, but the truck did not run that cool in the earlier years.
Some reading and research suggested that the thermostat was stuck open, and should be replaced.

I just installed a 190 degree unit per some recommendations.
The truck operates just the same, in fact, even in this mild ambient temp (70 degrees) I couldnt get the engine up to 190 without running it at 70 mph.

Im now thinking the thermostat i had in there was just fine.
Am I missing something?

My second question is in regards to the inner rubber thermostat seal....the manual shows the machined shoulder "notch" goes toward the thermostat....i could not get everything to fit nicely unless i turned it around with the shoulder notch fitted into the lift bracket. Did I screw up, or is the book wrong?

I saw a couple youtube videos where the installer showed installing the notched area toward the lift bracket. Everything fit nicely that way and i have no leaks.

Can someone here set me straight on this?
Thanks

 

[Iron Duke II]

 

[Solar1]

Thanks iron duke, yes I did see that video, thanks. That video shows the inner (large one with the notch) seal installing with the notch toward the lift bracket, which is opposite what the service manual shows. am I confused or is the service manual incorrect?

Could the extra cool op temp be related to the clutch fan not working correctly?

 

[Iron Duke II]

Thanks iron duke, yes I did see that video, thanks. That video shows the inner (large one with the notch) seal installing with the notch toward the lift bracket, which is opposite what the service manual shows. am I confused or is the service manual incorrect?

Could the extra cool op temp be related to the clutch fan not working correctly?

It appears to be the way I installed it.
http://www.dieselhub.com/maintenance/5.9l-12v-cummins-cooling-system-service.html

This is like the T-Stat in my 12 Valve. https://puredieselpower.com/dodge-p...degree-thermostat-with-2-sealing-o-rings.html/

Not really sure on your clutch fan question.

 

[Solar1]

thanks, I looked at the dieselhub procedure; I did not use the rtv sealant on the lift bracket...looks like I should open it back up and apply.

they spoke of the inner seal notch toward the lift bracket as well.
it does appear to be the only way it fits nice.
I used to think of the mopar service manual as the bible, not so much anymore

 

[GAmes]

You will find an error in the FSM every now and then. Be thankful we have one that is readily available, unlike the newer Rams and the other brands. If the seal isn't leaking I wouldn't put any sealant on the lift bracket. I never have. As for the temp, a $25 IR gun will tell you the temp your t-stat is opening at. The probe for the gauge is at the other end of the engine. A non-working fan clutch, as in not engaging, results in higher temps, not lower. One that has failed in the locked position will drive you mad with the noise but it can't cool the engine below what the t-stat is rated for.

 

[Solar1]

Hey guys, I did check the temp at the thermostat housing with a laser temp reader.
It stays about 160. It does not seem to ever open close cycle while idling/parked...
Could it be that a brand new Cummins brand thermostat is not closing?

I also notice my mileage is reduced and the exhaust smell seems extra rich. I read some articles suggesting that a truck running cooler will run rich, but Im not sure if the was concerning a 24 valve truck or a 12 valve like mine.

Now Im wondering if I should buy another thermostat and install it.

I have not been able now to get the truck above 165 even doing 70mph on the freeway. This cannot be right...any thoughts?

 

[Iron Duke II]

See if you can return it for a replacement. The seller should stand by a Cummins part.

 

[GAmes]

I agree, but before you make the trip to return it I suggest you test it. A pan of boiling water and a candy thermometer will tell you what temp it is opening. After posting on your thread I shot mine with an IR gun. It reads cooler on the hose side of the t-stat housing than on the engine side by 5 to 10 degrees.

With the four row aftermarket radiator I have my temp gauge seldom climbs above 1/2 inch from the vertical 190 mark. And yes, all diesels burn fuel more efficiently at higher temps. Running rich is a gasser term, not applicable to a diesel.

 

[BigPapa]

Your engine will not warm to operating temp idling. On very cold days, in the 20’s, I drive @ 20-25 miles before my thermostat will open. Also, while idling cold like you’re talking about, the fuel injected into the cylinder won’t burn completely, washing the cylinder wall free of oil that’s lubing the piston and rings causing undue wear. Our diesels don’t need to “warm up” like a gasser. Start her up and let it idle till your oil is circulating and drive away, gently of course. If I want mine to warm up before I leave, I deploy my High Idle Device, a cut off mop handle between the seat bottom and the accelerator pedal, to @ 1500 RPM.

 

[Solar1]

after a hard drive tonight with the radiator blocked 90%, I quickly checked the thermostat temp (Hose side, just after the thermostat) and measured 187 with the IR temp reader...the engine side measured 164. the 164 temp seemed to stay fairly even, but of course it was now at idle for a number of minutes.

Maybe I need to load my trailer and pull a load to get the temp up in order to check if it hold a max operating temp at about 190 or so.

all I know is that the truck used to run down the road(freeway) at 190, summer or winter, without blocking the radiator.

bottom line, it appears the thermostat is working, but the temp gage on the dash may be off somewhat. I do have heat in the cab, so I don't think there is any low coolant issue (I did check level by the way).

I just find it quite curious that the truck runs cooler now that it is 23 years old.

maybe I should shut up and be glad the truck is not overheating
I might consider a "High Idle Device" also to warm it up more quickly

 

[Cummins12V98]

Use exhaust brake to warm.

is your fan clutch frozen up?

 

[Solar1]

I can hand spin the fan blade freely, and get about a 1/2-3/4 revolution with a quick spin and release.

 

[BigPapa]

Use exhaust brake to warm.

Where did I miss he has an exhaust brake?

 

[Solar1]

I do not have an exhaust brake