Stock Thermostat for a 1974 250 4.1- 180 or 190?

[walkerb]

Now that my temp gauge is working and a rebuilt 3 row radiator is in, the gauge moves between just past half and the orange.

Gauge starts at 100 and tops out at 250. That would make the halfway mark 175.

Im thinking that the 190 that I put in is too much. Anyone know for sure that's suppose to be in it? Thanks

[walkerb]

Just checked the gm archive and its calls for a 195. I guess now I have to ask the 250 guys, where does your temp gauge sit at running temp?

[walkerb]

Nothing from the 4.1 guys?

[C10wip]

I put a 195 in a few months ago, along with a new radiator and heater core and I cleaned the system out. Now the temp gauge will move up to about the width of the needle above 3/8, then fall back to about the width of the needle above 1/4, then rise back up and continue to cycle, that is, you can see the thermostat opening and closing.
The radiator is the one for the larger engine sizes, but that shouldn't make any difference on the max point, which is what I think you're asking about. In the summer I would expect that it just won't cycle, it will just stay open.

[walkerb]

C10wip, is your temp gauge marked with C and H or by numbers?

[C10wip]

Pretty sure it's C and H, with 5 hash marks, so in my earlier explanation the middle or 3rd hash mark would be 1/2 and the needle vertical and the second would be 1/4. The thermostat is operating properly I believe; I checked the housing temperature with an IR thermometer to see when it was opening and it was close to 195.

[walkerb]

Gottcha, I did check with an IR also and its not going over 191.3 so I must have used a 190. But the gauge still reads 5/8 to 7/8(almost in the orange).

Im wondering if the new aftermarket gauge senor is bad or wrong? Nothing is boiling or overheating I think.

Just going from non working gauge to one that works after I rebuilt the radiator I have nothing to base from. No idea how the new gauge or radiator is working. Probably just being nervous.

[C10wip]

Could be due to a different sensor. I remember that getting the part number for the temp sensor was not so straightforward ( has been obsoleted and replaced or something ) and that there were a bunch of different resistance ranges which would then give different readings. I believe the one I used was AC Delco part number 2134793, from RockAuto.
The needle sits close to where I would expect it to on most vehicles so I assume it's the correct sensor; hardly scientific but that's what I'm going with now.

I don't know what the resistance range on mine is off hand, but if you can compare it to the one you have then maybe you can get an idea if we have the same sensor. Or, if you can't find out it out on paper, you could measure the sensor resistance when it's warmed up and compare that to mine. I think the resistance when cold is very high, i.e. not a useful number.

When I got my truck from the PO it had no thermostat, mud for coolant, a leaking water pump and a plugged radiator and heater core, and the temp gauge wouldn't come off zero which is why I replaced it ( and everything else ).