Let me just put it this way. If everything was working as intended, there's no way the analog gauge should have ever pegged at 260. That leads me to believe the ECT (it's called the Engine Coolant Temperature in my service manual) sensor must be sending erroneously low temperature readings to the ECM causing the fans to come at higher than normal temperatures. BUT, the ECM believes it's doing it's job correctly because that's the information it's receiving from the ECT. It only reacts to the ECT, it could care less that the temperatures are actually going past 250 on the analog gauge.

Also, there is supposed to be DTC codes thrown when that ECT sensor get's out of tolerance, I had none. Also leading me to believe that it's not off far enough to set a code, but off far enough to make sitting in the car on a hot summer day unbearable.

I'll tell you what, it's a hell of a band aid because I think without the band aid right now I'd be changing head gaskets frequently.

The cooling system mechanically now is 100% but you're right, the supporting electronics are what is broken. Or at least not operating the way they should.

 

Just my $0.02...

Both the analog temperature gauge and the digital temperature gauge get their readings from the same temp sensor in the engine bay. I don't believe that the analog temp gauge is accurately calibrated at the factory - it's more of a ball park estimate of the actual temp. The digital gauge, on the other hand, shows the actual reading from the temp sensor as interpreted by the ECM.

I would also tend to give more credibility to the digital gauge than the analog. It sounds as if the digital gauge and the ECM correspond on their measurements, indicating the temp displayed on the digital gauge is in fact the temp measured by the ECM. The Analog gauge is also driven by the ECM, but sounds as though the calibration on the sweep is off.

 

I don't mean for this to sound mean, but you are 100% completely wrong.

Open your service manual and you will see that the ECM reads the ECT mounted in the wter pump and the analog gauge gets it's information from the head sensor.

The sensor in the head is a one wire = Analog gauge

The sensor in the water pump is a two wire = Digital gauge and ECM fan control, among other things.

 

A quick way to test the analog gauge is to take that one wire off the sensor and alternately short the wire to ground and leave it open.
If I remember correctly, with the key on:
1) Shorting the wire to the engine block should make the analog gauge go to the bottom of the scale.
2) Leaving the wire hang open, should make the analog gauge go full scale.

This would test the gauge but not the sensor.

Tom Piper

 

Yeah, we broke one in half once during a header install, I can't remember which way it swung, but the ECM digital readout was unaffected.

 

Well in that case, ignore me. I apologize, I'm at work and don't have a service manual handy. That's interesting that GM used two different sensors - does the ECM regard one as more important than the other (just for my own curiosity)?

 

The ECM only looks at the thermistor in the coolant pump.

Tom Piper

 

One of my intentions with this thread is to see if any other LT owners have or had a wild temp difference between their gauges also. I think there has to be since we see LT1 owners time after time come here and report high temperatures. I feel I may be on the right track with the ECT going south and not turning the fans on at the correct time even though it does read 230-228.

We have also seen a lot of members report the analog going to 250-260, the ECT being bad and reporting temps too low could explain this situation.

Coming right off the bat with "this is normal" isn't helping solve the problem, in fact it may be harming some without the full story.

Honestly, when it warms up outside I'm going to get a new sensor and compare the old to new and see if there is a difference. Also compare them to the resistance chart vs. temperature listed in the service manual.

Yeah, the analog gauge and sensor for it are a complete stand alone system. You could effectively take the sensor and gauge out and no other system in the car would be affected.

 

In that case I'll let you know about my gauges - hopefully without demonstrating any further lack of technical knowledge.

I have not observed a vast difference between my analog and digital temp gauges. I have a '96 LT4 (current mileage around 28,000) that's had the water pump replaced. Shortly after the pump was replaced, the car ran hot. I burped the system several times, air bubbles came out each time, and after I was finished the temps were normal (fans came on at 230 on the digital temp gauge and off around 215ish). Even when running hot, the digital and analog gauges roughly matched each other. In my case, running hot was a result of air in the system and not a faulty sensor.

For my particular car, the gauges that don't match well are the digital and analog oil temp gauges. The analog oil temp gauge reads low and barely moves during operation. In my case, the digital oil temp gauge appears to read correctly, but I've never deep-dived the situation to verify.

 

My analog gauge reads about 10 - 15 degrees warmer than my digital gauge.

I have a 396, with a 160 degree t-stat, Dewitt's radiator, Elec WP, and the PCM is programmed to turn the fans on earlier. My car stays at 170 -175 degrees according to the digital sensor, while the analog sensor usually sits right on the 185 mark.

 

Just for the heck of it, assume one fan has its windings burned open..

Then when the fans try to kick on at 219, neither will come on since the fans are in series and the opened fan coil blocks the circuit...

At 228 the fans are told to go to high speed which puts them in parallel, so now the good fan runs and the bad fan still doesn't come on...

One fan will only provide marginal cooling....

So are you sure both fans come on or did just one come on at 228 (more or less 228=230)...

You wouldn't be the first to have a bad fan......or maybe a bad fan relay(there are three involved)...

Again, good luck on finding your problem..

 

I replaced both sensors on my 95 along with a bunch of other stuff when I redid my heads. My digitall and analog gauges read very close to the same temp.

 

GACELT4, Thank you, this is exactly the kind of thing I'm looking for. You see before I did the 160, fan reprogram, my temp gauges were way off, not lying when I say about a 30 degree difference. I really didn't mean to sound disrespectful earlier, but there really isn't an easy way to tell someone something they've typed is wrong.

LT4BUD, very good thought, I remember checking mine when I first got my service manual but should check again as there's no code to tell you one fan isn't working.

Cold_B, for whatever reason my temps act the exact same way now with the 160 and fan change. The only thing I can guess is one or both gauges become VERY unlinear at higher temperatures.

I want to see if I can make my car comfortable the way GM designed it, with the way it was sitting in the car on a hot summer day in traffic was unbearable. Most of the time like Wilson, my car would gurgle after shutting it down, god forbid I shut it down near 230 on the digital, I usually ran the ac until it got a bit lower. I swore off the changes for as long as I could take it because everyone here said, everything was normal. This all after a new radiator, t-stat, flushing the system and bleeding it 'till I bled. The heat from my car just got to be too much to take so I did the nasty (t-stat, fan reprogram) and worried no longer.

Something had to be wrong with that situation, I can't see GM making a car get that hot before turning a simple fan on. Anyone that says all this is normal is off their rocker, or at least doesn't understand what kind of heat can emanate from these things at high temps. NONE of my other GM vehicles exhibit those symptoms and one of them even has a 195 t-stat in it.

It'll be interesting to troubleshoot this, but I can tell you I'm not gonna waste a lot of time on it because the 160 t-stat and fan change works so well it's almost a shame to mess with it in the name of curiosity. I also have three other things I want to do to it this summer.

 

You posted while I was typing, very interesting.

Are you starting to see what I'm getting at? I think we have some LT1 owners with ECT sensors that going off the chart causing way too high temperatures.

 

Yes, I understand your point. That is why I replaced both. I don't know what the long term accuracy of these sensors are, but they are inexpensive to replace and since they serve a critical function (especially the ECT) I replaced them.

 

Here is a way to determine if the CTS (or ETC) is correct.

First, you have to know what temperature the thermostat is and then run the vehicle on the open road on a very cool day (hopefully, 50 degrees or less) without the A/C on.
After the engine is thoroughly up to operating temperature keeping a steady speed of about 50 mph or greater (but not pulling hard), look at the digital display.
With a 180 degree thermostat, the LT1/LT4 will read about 194 degrees.
With a 160 degree thermostat, the LT1/LT4 will read about 178 degrees.
Because this is a reverse flow cooling system with the thermostat on the inlet side of the engine and the CTS on the outlet side of the engine, the digital display will read the thermostat reading plus the amount of heat picked up by the coolant going through the engine.

If your digital display is in the "ball-park" of those readings, there is nothing wrong with it.

The CTS in my '92 is original and it has been consistent for 15 years.
But, I have had three Hypertech 160 degree thermostats and two of them gradually increased in their opening temperature until they were about 180 degree -- replace them and the temps came right down to what it should be.


Tom Piper

 

I’m thankful to say that this is my operating parameters also.

There are not many days that I don’t run the A/C in Orlando due to the warm temps and to keep the moisture down in the car. Due to this, there is usually a fan running which keeps me between 195 and 205 while driving. In slow traffic for long time it will start to creep up but will usually turn on the aux fan switch and start the second fan at about 215 or so.

Been cold this week in Florida in morning (40s) and am using the heat (no A/C) and as long as I am moving, I stay 195-205. You can bet if I stop for a while with no fans running the temps will start going up but will kick a fan on before 220 and problem solved.

My analog gauge is pretty close to the digital, all stock, 180* stat and 2 year old radiator which is slightly thicker (5/8") than the original one that I took out. Have not re-programmed anything, just control second fan manually when I need to.