Operating temp too low?

[Matt121]

I feel like the normal operating temp of my 5.7 96 Tahoe is too low, am i right?

This is where it is when it warms up fully


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[Danny3737]

Your thermostat may be stuck open or the wrong temp

 

[Matt121]

Ill check it out, thanks for the help


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[iCajun]

Agree with Danny as I just replaced one in a 454 that wouldn't close. However, it might be the gauge or sender. If you have a reader you can compare the gauge with the computer, or take a sensor resistance reading and look at the temperature sensor table.

 

[east302]

For comparison, I have a 98 Tahoe and truck. Both read like this when warmed up. I think both have the 195-degree thermostat.

If the upper radiator hose gets hot after a few minutes, then your thermostat is opening up. The tick marks on these dash gauges are hard to figure out and don't look to be linear, but with a scanner you can read the output of the coolant temperature sensor.

 

[retorq]

I have a 180 thermostat in my Tahoe and it rides just like yours does OP.

 

[Matt121]

When its really warmed up its at east302's mark, but i think i did the calculation a while back and thats roughly around 160-170 degrees, which seems kind of low to me.

Should i worry and fix it or its fine? My mpgs are shit anyway lol


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[willxfs]

I have a 1998 2 door tahoe. I have tried three thermostats over the years. 160 degree, 185 degree and 195 degree. The temp on the gauge would always read about 155 to 160 degrees. Just what Matt and East's pics show. Just yesterday I installed a new temp sensor. The one on the drivers side block just below the exhaust manifold. Now its reading 1 line above the 210 mark. (I think I have the 195 degree thermostat in now). Pretty sure that temp sensor was original to the truck. Seems to be reading a little high now... Temp sensor was pretty cheap on Rockauto. Good luck.

 

[Matt121]

Ill change the sensor and see what happens


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[jiggie]

Mine runs about the same as op and others and seems to be fine. None of the mechanics seem to have any concerns and say everything is normal. All the cooling system was replaced in feb and flushed. New sensors waterpump, coolant flush, etc


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[iCajun]

Sort of on the same subject, but the LT1 in my Impala had been running a little hotter every day for the last week. I replaced the thermostat for lack of a better idea and it went back to normal, to 200 from about 230 on the OBD2. I've never heard of a thermostat failing like that. Thanks, Alan

 

[iamdub]

Worse fuel mileage is only one of the problems running too cool will cause. The engine was designed to run within a certain operating range to help promote more complete combustion and it's cooling system designed to support and maintain this temperature range. When running too cool, the fuel isn't burned as efficiently. This can lead to excess carbon build-up in the combustion chambers and even clogging of the catalytic converters. When warming up, the engine can remain in open loop ("warm-up") mode for too long, meaning that the PCM is adding extra fuel longer than necessary in an effort to get the engine up to operating temperature. The excess unburnt fuel can also soot over the upstream O2 sensors. So, once warmed up and in closed loop, if it gets there, the sensors don't read the exhaust as accurately and report the exhaust as being leaner than it actually is. The PCM increases fueling thinking it needs to richen the mixture, further exacerbating the issues.

It's old school thinking to keep an engine running as cool as possible. Engines and their lubricants are so far advanced (yes, even the old Gen3 Vortecs) from those days that they can safely reap the benefits of higher combustion and operating temps. 195-215 is a perfectly safe and efficient operating range.

As far as the gauge is concerned, it may or may not be acceptably accurate. A possibly faulty sensor and the loose manufacturing tolerances of the gauge cluster, typical of this era, leave this aspect to be questioned.

On the flip side, having a thermostat stuck open or even no thermostat can actually cause an engine to run hotter, especially during hot weather and when cruising. The coolant needs to flow to carry the heat from the engine and through the radiator to be cooled so it can go back into the engine to repeat the cycle. If there's no restriction (stuck open or no thermostat), the coolant may not remain in the radiator long enough to be cooled sufficiently so the operating temps rise.

You may be fine burning extra fuel because "it gets crappy mileage anyway", but it's actually costing you more than just more frequent trips to the gas station.

 

[iCajun]

Curiosity got me so yesterday I put a 180 ohm resistor between the sensor wire and ground, which I understand should read 212 degrees on the gauge. Mine read a little low. Think I'll pull the temperature needle off and re-position it eventually.

 

[OR VietVet]

You would be best to attach a scanner to the system and get an accurate reading. The correct thermostat, 195 degree, is important to help the system go to closed loop and allow the oxygen sensors to operate correctly. Your crappy fuel mileage could be because your system is constantly reading open loop, like right after you start and engine is cold, and more fuel is supplied to be burned during warm up. Like a choke on an old carb type system.

 

[OR VietVet]

Curiosity got me so yesterday I put a 180 ohm resistor between the sensor wire and ground, which I understand should read 212 degrees on the gauge. Mine read a little low. Think I'll pull the temperature needle off and re-position it eventually.

Good luck with that endeavor. Have a new dash gauge to install when you break the old one trying to do that.

 

[HERC1969]

Mine runs at exactly those dial numbers 50-60C for temperature, runs good, no issues on a new 195 thermostat and flush. The thermostat opens between 90-100C, so everything appears to be in working order. As a side note, my oil pressure is between 140-275kpa dependent upon engine load.