How trustworthy are the factory gauges?
 

For some reason, I have bad luck with new to me vehicles. They always seem to have overheating issues. My first project with this one (94 Z28) is to track down a small coolant leak. I am considering installing an aftermarket temp gauge once the leak is found and I am certain the cooling system is sound, but wanted to ask about the factory gauges first.

I hope I'm not hijacking here, but I don't really understand the purpose of aftermarket temp guages? The whole idea is to alert you of a cooling system problem. Even if the stock guage is off by a bit, does it really matter? It will still alert you if there is a problem, albeit a little earlier or later?

Stock gages are not accurate and vary in how well work. Temp amd oil pressure are the worst. They are only slightly better then a dummy light.

they go up and down with temp. best to check with mechanicial gauge to compare. could test temp/ohms at sensors to see what they are reporting to the computer and temp gauge and compare. if both sensors are seeing 190 and gauge is reading 160 then you now the gauge is off. http://shbox.com/1/4th_gen_tech2.html#ect


ECT Temperature vs. Resistance Values

∫C ∫F Ohms
100 212 177
90 194 241
80 176 332
70 158 467
60 140 667
50 122 973
45 113 1188
40 104 1459
35 95 1802
30 86 2238
25 77 2796
20 68 3520
15 59 4450
10 50 5670
5 41 7280
0 32 9420
-5 23 12300
-10 14 16180
-15 5 21450
-20 -4 28680
-30 -22 52700
-40 -40 100700

Use a Digital Volt Meter (DVM) set to ohms to measure resistance. Note: Use a high impedance meter (at least 10 megohm) when dealing with the PCM. Most modern DVMs will do, but your old analog meter can damage the PCM. It is also a good idea to get a " reference" from the meter you are working with. With the DVM on the ohms scale, touch the two meter leads together and note the ohm reading. It may not always be perfectly zero, but may be within a tenth or two. Now when you take an ohm reading, you will know what the meter will show when there is really no resistance.

A quick gauge calibration, feel the radiator hose.
When hose becomes hot, the 195°F thermostat has opened.
Look at gauge at this instant for self-calibration.
Thanks for the chart.

"Most modern DVMs will do, but your old analog meter can damage the PCM." Thanks for this Craby. The meter I have was my fathers and it has been for a slong as I can remember. I will get myself a newer one. And thanks for the input everyone.

For me having something better than the equivalent of a dummy light is important. Summers here can be brutal and a little advance notice of an overheating problem can make a big difference.

I installed an aftermarket gauge the other day. My dash water temp light was way off. Now I know what the approximate temp is. Next I'm gonna do the oil pressure and tach. The spedo is fine the way it is for now.

Mind if ask where you installed it?

I think there's a common problem with these damn things. My 94 has had a problem ever since I got it. I've replaced literally everything in the cooling system and still had problems so I just rode with it and now she's sitting with a BHG. If its anything like mine, prepare for a long, long fight...:icon_starwars:

I hope not, I am tired of vehicles that overheat. If this one turns into a long fight, the car will go away. I usually prefer older cars than this, but since it was a gift I figured I'd give it a shot.