Engine/Transmission (1994 - 1998) Help please with thermostat inner seal position

[Northrunner]

Hi Guys,
This has puzzled me for a while...that inner seal for the thermostat has the cut shoulder on one side. Every installation instruction I've seen says to place that inner seal with the shoulder facing the thermostat. Is that truly right? It seems to me that it should be facing away from the thermostat so it can go through the lift bracket hole (it fits that hole perfectly like it was designed to go through it) and just touch the engine block and thus create a waterproof seal when the 3 thermostat housing bolts are tightened up.
That is how the one in my truck is put together. If it was installed with the shoulder facing toward the thermostat, then upon tightening up the bolts you would have the lift bracket directly against the engine block with no gasket of any kind, metal to metal. How could that possibly not leak? Plus, can it really be put together like that? That way seems like since the seal is not going through the lift bracket it would not even go together.

Reason I ask is years ago when I bought my truck used, it had a stuck thermostat. After buying a new one as I was installing it I got to this point and was not sure which way that seal faced. I went and bought a Haynes repair book and it showed the shoulder facing the thermostat. It sure seemed to be designed to go together the opposite way and I thought the book was in error. Anyway, I put it together with the shoulder facing away from the thermostat, through the lift bracket and it worked fine for years. Recently my dash temp gauge needle barely moves off the coldest area of the gauge so I thought the thermostat was stuck open again. I bought a new Cummins thermostat and installed it just like the old one with the shoulder facing away from the thermostat. It all goes together perfectly with no leaks but still I can't get the needle to move off cold. My heater works fine but even after a 20 mile test drive, still running very cool. Temp gauge needle just barely moves off it's resting spot but no more than that.
Today when I was putting it all together I again evaluated the situation. With that shoulder facing away from the thermostat, that seal fits in the outer housing on top of the thermostat snug and perfect. The opposite way it fits all loose (because of the shoulder) and can move around on the thermostat not being centered plus it seemed that it would not all go back together without the shouldered side going through the lift bracket.

Am I missing something obvious here?? Still puzzled in Idaho...thanks for any help.

 

[Jeff L]

Grab the housing, install outer seal, install thermostat (pay attention to "towards radiator" marking), install shoulder of inner seal into housing and against thermostat, install lift bracket over seal and onto shoulder, put the three bolts in place (short one on bottom), place entire assembly on block, then tighten to spec's.

* before you put the assembly back on, reach into the block with your fingertip and locate the end on the check valve (jiggle pin). It's a checkvalve designed to close when under pressure, and if it's not closing, coolant circumvents the thermostat and the engine won't warm up (which might explain your operating temperatures).

 

[GAmes]

If the heater is working I'd suspect the temp sender on the rear of the head or maybe even the gauge. Have you checked the temps with an IR heat gun at the top radiator hose? BTW, the Haynes is good for emergency toilet paper. Genos sells factory service manuals which include complete wire diagrams.

 

[Northrunner]

Thanks for the replies guys. Since my original post I've learned that the directions about the inner seal's shoulder facing the thermostat is an error. Shoulder apparently should face away from the thermostat so I guess I've got that together correctly. Also I took the old thermostat and put it in some 190 degree water and watched it open, then put it in cold water and watched it close. I did that cycle several times so I guess there was nothing wrong with the old thermostat in the first place...lesson learned there.
Then I tried to check-out the temp sending unit. That was a dead end, I can't even find it. I'm told it's on the back of the block, drivers side, below the lift bracket. I could not see it, I can't feel it, I got a mirror in there with a good flashlight and still could not find it. There's nothing back there that looks like the sending unit. I called Cummins Northwest, gave them my engine number, they told me it's located back there where I was looking. I'm stumped and giving up. I've got to have that gauge working for an upcoming hunting trip and don't have time to screw with it any longer. I'm gonna make an appointment at Cummins Northwest and let them figure it out.

 

[GAmes]

Does this help? http://s453.photobucket.com/user/Ch...w cab Cummins swap/coolanttempsender.jpg.html

 

[Northrunner]

GAmes,
Thanks for the pic. On my truck I can see that spot but instead of a sensor there is just a plug in that hole. Weird...now I hear on the 98's the sensor is on the left side of head near the fuel filter and fuel pump. I've been looking there...damned if I can see it. Jeez what a pain...I remember when I was in my twenty's and enjoyed working on motors...those days are sure long gone!

 

[GAmes]

GAmes,
Thanks for the pic. On my truck I can see that spot but instead of a sensor there is just a plug in that hole. Weird...now I hear on the 98's the sensor is on the left side of head near the fuel filter and fuel pump. I've been looking there...damned if I can see it. Jeez what a pain...I remember when I was in my twenty's and enjoyed working on motors...those days are sure long gone!

That IS the left side of the engine, the filter and lift pump are clearly shown. I had a '98 12 valve engine for awhile, the sensor location is the same. If the connector is broken off the sensor it will look like "just a plug".