Cal Vette

I know this is a widely discussed topic, but just have a quick question. How accurate are these idiot gauges?
My needle does not give an accurate temp. 2 pics. One on freeway, the other in just a few minutes
in traffic. Seems to stay in the middle, except for when I stop for a while and idle. Is this something to
worry about? Looking at the gauge it appears to at 240+

jon1all

The analog gauge is close, but not great. Use the digital one instead if you really want/need to keep an eye on temps.

That said, these these cars do run uncomfortably warm (by design I might add, but still alarming to see nonetheless). Try putting some manual override switches on the fans...that definitely helped me (I love in Phoenix).

Nomake Wan

From the factory these cars came with a decal on the instrument panel (ostensibly removed by every single original owner) which reminded the owner that the analog gauge is not a linear device. Just because the gauge's lower scale says 100 and the upper scale says 260 doesn't mean that the middle of the gauge equals 180. It doesn't. Likewise, the only part of any of the analog gauges you have to worry about is the hash marks. If you're in the hash marks, you have a problem. If you're not, you don't. Also, the digital temp gauge is for a sensor on the water pump housing, while the analog gauge is a sensor on the passenger-side head, for reference.

So first off, go by the digital gauge, not the analog. Second, if you're ever concerned about the water temp, there are a set of basics to go over.

1. How is the cap on the pressure bottle at the back of the engine bay on the passenger side of the car? If this has never been replaced, the seal is probably goo. Replace it so the system can reliably hold 15 PSI.
2. Are there any leaks in the cooling system? Heater core, for instance? If the system cannot hold 15 PSI, it won't be able to run cool because the coolant will boil at a lower temperature than intended.
3. Are both fans operating? If not fix them. If they are, as jon mentioned, you can either wire a manual switch to click them on at a lower temp, or join the wonderful world of burning new chips for yourself that have modified enable temperatures. I haven't looked at the BIN from a '91, but in general GM doesn't kick the fans on until really, really high temps (on the LT1, the first fan doesn't come on until almost 230F, and the second not until nearly 240F!)
4. Is the entire radiator and A/C condenser area clear? If there is any debris either on the front of the condenser or between the radiator and condenser it will severely adversely affect the car's ability to stay cool. Our cars have a reputation as vacuum cleaners in this area.
5. Is the cooling system full and bled?

That's the basics. On top of that you can try doing things like running a lower temp thermostat (stock is 195F, I believe), but yeah.

miles71

On my 95 C4,
The Analog Coolant Temperature gauge is 15F degrees higher than the dash Digital display gauge.
My Analog Oil Temperature gage is only about 2-3F degrees higher than the digital display.
I also tried a Handheld infrared pointing at the engine thermostat and then compared to the Digital dash gauge.
My best guess is the C4 digital gage is closer to the infrared meter readings.
In other words, the Analog is way off.

My engine when Moving, runs consistently at 200F-Digital on most days and sometimes hits 210 on a hot day in Boston traffic.
If I Idle my engine for 20+ minutes,[45F, AC Off] parked waiting for food at a takeout restaurant, the engine will quickly go up to 240+F.

Note to self. Never Idle for more than 20 minutes.
Someday I will buy a Dual core Radiator.
Installed a 180F thermostat, with extra 1/8" drilled air-bubble by-pass holes

RollaMo-LT4

You really can't tell the real temp on those factory analog gauges.
They do not have a linear scale. As long as the needle does not actually go into the shaded area, you not over heating.

Use the "gauges" button, and scroll through until you see the coolant temp. That will give you a much more accurate reading.

BlackC4gca

how do I check my digital coolant temp like what buttons do I press?

miles71

If your C4 has this set of buttons, you can click on the Gauges button to switch between the different temperature settings, oil, trans, engine, etc.