E-Rod

Hi, all! I've been on here for a while, but have never really posted much.
I've had my 87 NA FC for almost two years now and just recently got it running after getting a new engine, overhauling, etc.. Everything seems to work fine, except I'm having a problem registering an accurate temperature reading. When I got the car, it was a carb'd 13b with a really messy harness. It's now EFI with a new harness and ECU. The previous owner installed an aftermarket temperature gauge, which was working fine on the carb'd motor(the dash gauge didn't work). But when I first started the car, the temperature read all the way to H upon turning the key to on position, on both gauges. After running it for a few minutes, the aftermarket gauge stays on the highest possible reading, and the dash gauge starts on H and slowly moves down. After finally reaching what seems like full operating temerature, the dash gauge now starts on C, and the AM gauge still on H. I've replaced the temp sensor on the filler neck twice and haven't had any luck. I cleaned the contacts and traced all the wiring and can't seem to find any broken wires/shorts. This is a big problem, I would rather not run the car until I can monitor the operating temperature accurately, it's really the only thing keeping me from proceeding with the build.
I've been told the polarity on the sending unit could have been reversed by putting the wires on incorrectly, but I don't see that being the case since I haven't touched the connector, and it only fits on one way. Even if that were the case, I doubt this would constitute overheating because I didn't run the car long enough for that to happen, only long enough for the thermostat to open and start circulating coolant. Water pump is also brand new, new belts, no leaks.
Please help, any leads are appreciated.

-e-rod

misterstyx69

iTrader: (142)

easy solution?..
buy a cheapo temp gauge,and install it.Get rid of the other old AM gauge and sender.At least you would know that the parts you now have are mated to work with each other.
the Stock sender is on the drivers side near the oil pedestal..a little pencil type sender with a little nub on it.Try to see if the wire there is disconnected.

E-Rod

Wow, there are so many sensors on the cooling system I completely forgot about that one. Anyway, I checked it and it's plugged in. Maybe it's just bad? I'd rather not go the "easy route," I'd like it if everything on the dash was working. And it all works except that. So I guess I'll try replacing it first..it's probably cheaper than an AM gauge anyway.