Hi,

I've installed a new crate engine, 5.7 Vortec, in my 99 Suburban K1500. It's got around 1k miles on it now.

The temp gauge is reading around 230. I was worried about it and about to pull the radiator and have it cleaned (already tried a couple different t-stats) when I remembered my scanner has the monitor function. The temperator on the scanner parks at 195 and stays there (at least while sitting in my driveway idling in 100 degree weather).

Why would the gauge and the scanner disagree so widely?

Am I correct that the computer is getting it's signal from the sensor on the head? Does the gauge get it's info from the sensor on the t-stat housing?

Thanks in advance!
Rusty

 

your temp guage gets its reading from the one on the driver side of the engine
your thermastate i believe it works by a small wax pellat inside of the hosuing that when gets hot opens you tstat

 

Check for a corroded connection tot he sensor that cubpack89 mentioned. It's the one by the exhaust manifold. I had the issue of my temp gauge being intermittent, and it turned out that the heat had eaten away the copper inside the wire shield just before the connector ... so make good and sure that it works. You can also use your volt meter to make sure the sensor works:



Both sensors work the same way, except the one for your gauge grounds to the block, and the other grounds through a wire and then to a stud on the coolant inlet. Use the volt meter to measure resistance on the sensor.

It could also be a malfunctioning gauge.

It's a simple circuit. 12+ goes the one side of the gauge, then goes out to the temp switch/coolant sensor, and runs through the thermister and grounds to the block. The lower the resistance, the hotter the gauge shows, the higher the resistance, the lower the gauge reads. It can also be a bad sensor. Check it according to the resistor values I gave.

Edit: Some service information will tell you to set the sensor in a known temperature water and test it that way, but the easiest way is to let the engine cool down, and double check your readings with what you have for your ECM temp sensor. It works the same way, but you can put both your leads on the sensor and it will work. The one on by the exhaust manifold, you need to connect your positive to the sensor, and your negative to the block somewhere. The readings will make sense, I suggest letting it set overnight, and checking it in the morning when the cool temperatures will be about the same with your engine coolant.

If all else fails, get your gauge cluster rebuilt or try to get a new gauge.

Edit2: I just noticed that your vehicle is newer than mine, so your circuit might be different. Get a Haynes manual from Autozone and look in the back at the wiring schematics to double check how the circuit works. The sensor might be labeled as a "temperature switch" so look out for it.