My apologies to youngblood as I hijacked his thread, so I figured I start my own.
91 Z28 350 dual fans. The goal is to get my gauge to read (at least close) to the 238 driver fan on and 220 off parameters set from the factory. At the moment the gauge is way off. Here's what I've done:

-Replaced the gauge sender on the L-S side of the block with a ACDelco part
-Replaced the R-S fan sensor on the R-S of the block with generic replacement part
-Replaced ECM coolant temp sensor on the front of the engine with a generic replacement
-Replaced the ECM
-Tested gauge by grounding the L-S engine sender lead. Gauge pegs as it should. Can't rule out a malfunctioning gauge, but the needle is free and actuates across the entire temp range
-Topped off with fluid


The following is what happens once the engine is started and comes up to temp. The vehicle is stationary and doesn't leave the garage for this test. I have TunerProRT hooked up and monitoring the engine data as well.

-After a few minutes the needle on the temp gauge pegs to the right above 260 without either fan coming on. No sign of boiling coolant.
-After many more minutes the L-S fan comes on when TurnerPro RT shows an engine temp of 110 then shuts off when the temp shows 105.
-R-S fan never came on


Why would TunerPro RT show a temp of 110 when the L-S fan comes on? I would've expecting this reading to be the closest to 220 since this is the main point of reference for the system.

I promise to continue to search and read previous threads created that are related to this subject, but I thought in the meantime one of you would deliver that perfect nugget of info I need. TIA.

 

I would also add that I'd like to keep things stock without the addition of rheostats and the like. I'd like to solve this problem within the confines of the design from the factory. TIA.

 

My gauge reads about 30* hotter than it actually is. If your temps don't spike to 240+ with an IR thermometer on the thermostat housing, then I would definitely see about getting a new or at least after market temp gauge to see how that reads.

 

I think it is non-linearity in the sending unit that you will never get rid of. When I was using stock fan settings in my TPI converted G20 van (like a day, tops) it would nearly peg my 260*F gauge before the fans would kick on. This was using a 3-wire sending unit from a 3.8 car that has the ECM and Gauge thermisters in the same sending unit and it was located in the intake manifold. If the gauge sending unit had been in the stock location in the cylinder head it would have read even hotter.

 

110°C = 230°F

105°C = 221°F

Sounds like it's not too terribly far off

 

Celsius?!? WTF? Does Tunerpro indicate that it's Celsius? Did I miss it? Thanks very much sof.

 

I don't know whether it does or not; but I'm a physicist (among other useless things), and travel internationally a lot, so I pick up on those co-inky-dinkys rather quickly.

 

Well done sir. As an engineer, I probably should have seen that. This is 'merica after all, so I went with F.

 

I think Tunerpro defaults to using temperature values in degC. i recall having to change all my tables and such to degF. (since i went to college in America......!)

 

Huh. Well then. If that's true, then I suppose I can assume the following:
-The ECM works
-TunerPro is capturing accurate data....even if it is in deg C
-The new temp sensor in the front of the block is operating as it should
-L-S fan is working properly

If all of that is true and my gauge is still pegging in the red, then one of these is the issue:
- New ACDelco temp sender is broken (Possible, but not likely)
- New ACDelco temp sender is inaccurate (most likely)
-Gauge is broken (tested gauge and needle moves...doubtful)
-Leads are worn (doubtful)
-Gauge is reading correctly and that part of the block is actually that hot. Water pump?

Gotta be a gauge/sender/associated wiring issue. Anybody ever re-position the needle? Is that an option? (never had one apart) Anybody add additional resistance? Thanks all.