Engine Temp Question

[zy5 guy]

So I have a question about the temperature gauge. Temp gauge never worked until I realized it wasn't hooked up. Found the wire for it and hooked it up the other day. After driving the truck around for awhile the needle would only go up a quarter of the way on the gauge. Truck by this point should've been up to operating temperature. My question is, what does your gauge normally show for a warm engine? If it is higher than what mine is showing, what else should I look at? Could the sending unit need to be replaced, or the t-stat? I do have plenty of heat when I turn the heater on. Not sure what degree t-stat I've got. Here's a picture showing just how far up the needle made it. Truck is a '77 with a 305. Thanks! -Evan

[gramps77]

yours is right about where mine usually is

[Goldfinger]

Mine has the numbers. but that's about 160 where mine sits. normal.

[jhngardner367]

Yeah,my '85 with the 305H sits right there,too,unless I'm pulling the trailer,and then it might go up a bit.

[zy5 guy]

Thanks for the input...guess I won't worry about it then. Probably wouldn't hurt to get a coolant flush done at some point though. Maybe I'll change the thermostat at that point.

-Evan

[Troy 82]

I have a 180 stat & mine is on the first quarter mark. Checking ohms of the sender says it's 180. I have a question though. I have two of the gauges with the numbers instead of the C & H. I tried both & they both read the same but higher than the C&H gauge. They both read between the 180 & 210. Closer to 210 actually. What up with that? Could the gauges with the numbers just read higher?

[rwhit57]

Mine reads 100 for the low, 210 in the middle, then 260 for the high. I've seen several different variations of the fact gauges. It all depends on how they are set or graduated from the factory. If mine was in the middle you'd think it would read 130 but that is not so. Mine runs a little above the quarter mark and I assume that's 160-180 hard to tell.

[Corts60]

My truck runs at the quarter mark as well.

[hatzie]

I plotted the resistance (Y) vs coolant temp (X) of the GM sender in excel based on some published sender data. The data starts at 20 degrees and ends at 250 degrees. This gives a more visual representation of the non linear sender behavior.
The fuel sender is an interesting weighted curve as well. The first @11/16 of the tank sweeps across 1/2 tank on the gauge. At 1/2 tank shown you only really have just over a 1/4 tank left. At E you still have 1-1.5 gallons reserve. According to one of my GM service news in the mid 70's (somewhere between 73 & 75) GM weighted the fuel gauge this way to give the impression of better fuel mileage. My F250 plow trucks' fuel gauge is weighted the same way.