So do you think I should be concerned on how high my gauge is reading before the thermostat opens? My gauge was around the line between 210 and 260, I let it open and close three times and it averaged getting too around that line a little past it everytime before dropping to the 210 point. If that’s normal I won’t stress about it too hard but that shows in my opinion it’s getting closer to 240 before it drops to only 210. I do have to say the heat blowing out was pretty nice. Although not worth it if thr trucks going to run hot
I would double check your gauge sensor because you said its new and they changed a lot and no idea if that includes the 87 tbi or not for specialty. plus the replacement could be an oopsie replacement. Your numbers of course on the gauge wouldnt know if the Ohm scale its built on is shifted different than the factory sensor.
Also, your ECM has a separate sensor, have we confirmed that THIS sensor is reading the temperature accurate to the one seen on the gauge, you need an ALDL reading software or scanner($$$$$) that was referenced at the beginning by
@Vbb199 about his phone app and a plug in part I think it was bluetooth too. ALDL live data is slow and minimal but its critical we are understanding things as the way your computer understands them. IF you have a variance from factory spec, then you will never get it where it should because its not working on the same assumptions and thus can vary dramatically.
There is also a way to check the pins with your voltmeter but you need to find what voltage it is cold, hot, and what it would realistically scale to. I dont know if the 1987 model year has a dual range sensor or not, but GM used dual range sensors at least in 1990 which had a shift in what the sensor would report in different temp ranges but using the same sensor, because -40 to something above 230 isnt reasonably doable or accurate for a thermistor with one range, Is my understanding. Like, the extremes of the sensors would not be accurate past a temp or something. I believe its a 5v reference which means 3 wires(all go to PCM, 2 being hot on key on) or 2(if 2, both go to PCM) with the threads going into an intake that grounds to the same point the ECM Does... which... is on the intake...? Firewall? I remember reading about all this, something to do with isolated intake from the engine with a groundstrap to the firewall. While I say that, what kinds of grounds you got? Its just critical your engines TBI and engine sensors hanging out on the intake are grounded in a different path than something like a alternator case being wired to the same spot or where a engine block ground is. The ECM should also use a ground path without something like a window motor or a electric choke or a engine to fender ground is either. Stuff like that.
On your radiator cap, once your thermostat has opened, your radiator would go down.You add to it to keep it from going low, but once you see its stopped taking it down, like much at all, fill it and cap it. Your system needs to pressurize to be the right boil protection but your system does need to be open to fill it initially. You want to put a good amount in your overflow so it doesnt suck it low/dry(ha) and if you want to be sure, you can buy a lever release cap and safely release pressure if you want to check your work. But with a NEW cap thats working right, you should just fill it, start it, fill what gets circulated right away, then wait for it to warm enough, it will open, then you fill and when its not going down, its probably pretty darn close. Thats when you fill and cap, then double check your reservoir to have enough in it so it can overflow into but more importantly, have some in if it, say, shoots air out when it gets hot, then has a void it can pull coolant back inwith it. cooling down is what draws it in.
Check your sensor, check your dash ground, check your PCM for data or your PCM sensor for the voltage. Double check the spot on the intake where the sensor is with a heat gun and check the head next to the sensor and check your dash.Even a hose or the water neck to be double sure. you should see different numbers but they should be rational. The one on the intake is the sensor because the value works better for PCM stuff and it better represents the temperature for stoichiometric AFR than the cylinder head temp would. however that is is above my paygrade but they are quite the eggheads and gm doesnt like to piss away money on things except when they do but those things have a odd connection to eachother. this aint it. but science.
