[KeithO]

My fuel gauge has always been wrong on my 1995 Firebird. When the gauge comes off full, I know that I need to get gas fairly soon for street driving and immediately for track driving.

Yesterday through the use of a scan tool, I also learned that my water temperature reads way too low while also learning that GM has two water temperature senors in the car - one for the ECM and one for the fool behind the wheel. The ECM sensor seems correct and the in-dash water temperature gauge is wrong.

Should I be treating these two problems as separate or is it possible that these are related?

[Jon A]

It's possible when you observed that difference, the water coming from the radiator hadn't been through the engine yet. It will vary depending upon a lot of variables.

I've found when it's settled into a nice steady state, lightly cruising so the engine isn't producing much power at all, the gauge only reads a couple of degrees below the PCM. When you put your foot into it very long, the difference gets much bigger.

I was actually planning to move my sensor for the gauge to the same spot as the PCM a while back as I think the coolant temp after the engine is the more important one to monitor. I just never got around to it. I'm glad you reminded me. (IMG:http://www.frrax.com/rrforum/style_emoticons/default/wink.gif)

Don't get me wrong, your gauge certainly may be off. I'm just trying to point out it really is reading a different temperature, so it might not be. You could always swap the sensor location and see how it works. An aftermarket gauge would be nice, but if you're on a budget it's nice to know something really is broken before you replace it.

Let me do some searching of my notes...there's a Corvette sensor that fits where the PCM sensor is except it has a wire for the PCM and one for the gauge. I forgot all about that mod, I guess I got too busy last year. I just kept in the back of my mind that whatever the gauge said on the track was probably 10-20 degrees or so lower than reality.

[Jon A]

I just kept in the back of my mind that whatever the gauge said on the track was probably 10-20 degrees or so lower than reality.

SAE 920673 New Generation Small Block V8 Engine has a nice graph of coolant temp as it travels from the front to the back through the heads, then from the back of the block to the front (this is why the middle coolant passages in the head gaskets are mostly blocked off, to force the water to take this route). It shows a temp difference of 8 degrees from entry to exit. Unfortunately it doesn't state under what conditions it was obtained--full power or cruizing, etc. My experience inclines me to believe that's just cruizing.

Anyway, here's the info on the Corvette sensor for the water pump:

10096181 PCM/Gauge sending unit.
12102748 Connector pigtail (incl. terminals) (Superceeded by 88988301).

The new sending unit is wired as follows:

Pin A = Black, PCM sensor ground
Pin B = Yellow, coolant signal to PCM
Pin C = Dark Green, to Gauge

I'll be using this unit with the new engine as well as the old one. Switching the guage from one location to the other is as easy as unplugging the green wire from one and plugging it into the other. Once I get some data on the difference and verify gage accuracy I'll leave it in the pump and the unit in the head will just be a plug--unless the stock one really is off.