I noticed that my Digital Temperature Gauge reads about 15 degree's lower than the Analog Gauge. Normally I wouldn't care, but when the digital gauge reads 228' and the 2nd fan kicks on, the Analog Gauge is right between the last mark and the Danger mark. How can I verify which one is correct and if the digital one is reading low, is there any way to kick the secondary fan on sooner. I did change out the temperature plug in the water pump on my last install. Is there any way to test this item. One last thing. Can someone tell me if the Digital and Analog Gauges both get there readings from the same point. Thanks in advance for all your help.

Harley

 

My contact at the Chevy dealership said trust the analog.

 

I know 2 completely separate sensors drive them, but not sure which is "more accurate" The sensor that is part of the water pump housing is the digital one, IIRC.

 

Geeez, a mechanic will always say to trust a analog as they are most never digitally smart. If you as you say replaced the temperature plug there is always the chance of damaging a part with the wrench. Not saying this is what happened but I myself have damaged a sending unit unknowingly by over tightening it or what not.
Olcrusty said that

 

mine is like that too.

 

Here is my understanding:

What you described sounds about right. Mine is the the same way, the digital readout is 10-15 degrees cooler than the analog gauge.

One of the above posters is right about there being 2 different sensors.

The digital gauge's sensor is on the water pump right BEFORE cooled coolant coming from the radiator enters back into the engine. The analog gauge's sensor is located lower in the block.

The LT1 (I am assuming your car is a 92-96) is reversed cooled. The heads are cooled before the block to allow higher compression. So the coolant passing by the digital gauge's sensor is going to be cooler since it hasn't been through the heads yet like cooland that is about the pass by the analog gauge's sensor.

228* temps are not unheard of in LT1's and mine hit those temps all the time before I fixed it. I had my radiator rebuilt and added a 160* thermostat. Now My temps never get over 200 degrees unless I am racing or sitting ilding for a long time. Heck, they rarely even get past 185! Right now with typical outside temps in the 30s-50s in Texas, my car temps are usually in the 165-170 (digital gauges) and right on or even below the 185* hasmark on the analog gauge when fully warmed up. Before I had the radiator cleaned, it would get well over 200 VERY QUICKLY when idling or racing. I removed the radiator and took it to a radiator shop. They popped one the the side tanks off and ran a flat bar through each tube. Half the tubes on my radiator were clogged after 15 years. It was probably operating at less than 50% efficientcy!!! Having the radiator cleaned out made a night and day difference. In hindsight, I really didn't even need to do the 160* thermostat. I didn't realize how profound of an effect having the radiator rebuilt would be. A LOT of posters don't realize you can have a radiator rebuilt like this. Most just assume that if the inside of a radiator gets clogged over time that you just need a new radiator. That is 100% wrong!!!

 

You have described what I have been experiencing for four years. I also replaced the water pump sensor and still experiencing the same problem with the fan not turning on until the 'danger zone'. Interesting enough, when you unplug the water pump sensor, the fans turns on and the digital gauge appears to keep working in that the temperature does not remain constant but it does rise! Obviusly the temperature is not correct. Still trying to figure out where the problem is.

 

Trust your digital gauge--the analog gauge by design(linear) is not as accurate. BOTH of your fans should should run at the same time--low speed and high speed depending on engine temp.

There have been many threads/posts about engine temps, they were designed to run hotter from the factory then some (including myself) are/were used to seeing. I was not comfortable seeing temps 220-230ish---the PCM can be programmed/"tuned" to turn on the fans earlier. Since I had this done ,temps stay around 190(Digital) in summer heat---178-180 in winter using the stock 180 thermostat. Opinions vary from member to member on this forum as to whether or not changing the fan "on" temps is a good idea....personally I'm glad I changed mine.

 

Twisterup, Before you reprogrammed your fan turn on temperature setpoint, were you experiencing the same symptom as described i.e. high analog temperature versus digital reading?

 

My analog temps were and still are roughly 10-12 degrees hotter then digital temp.

 

Just did a trial on my 96 LT1, I let the car run idle while monitoring the temperature gauges. My fans did turn on low speed around 230*ish and my analog gauge was on the hash mark before the 265* mark. I may be wrong but there is a strong possibility that my sensor for the analog gauge may be flakey. Looking in the FSM to see if there is a test for the block temperature sensor. It's cheap to purchase but a pain to replace.

 

There are two sensors but the analog gauge is not linear. The halfway mark on the analog (between 100 and 260) is not 180, it's closer to 200 (the factory recommended operating temperature). Pick up or borrow a laser thermometer and check its reading against your digital gauge.

 

http://findarticles.com/p/articles/m...8/ai_n8912772/
I'd read this online a while back---the analog temp gauge is in fact "not linear"----In my case the digital gauge (before and after programming fan on/off temps) has always been accurate.

 

As other have mentioned, it's hard to tell exactly what temperature the analog gauge is reading.

Look real close at the analog gauge, and you will notice a shaded area. The max reading is 260 on the gauge.
Now watch the needle really close as the car is heating up. The needle will get very close, but not actually into the shaded area.
At that reading on the analog gauge, your digital gauge will be in the 225 - 230 range and the fans will come on.

So, it's not really getting to 260. But since the gauge isn't linear, you really have no idea what the reading really is.
At any range, the analog gauge is usually about 10-12 degrees hotter than the digital, because the temps are taken from two different places.
So, at 230 digital the analog is around 240-242. That would be just before the shaded area, and not pegged all the way to 260.

If that is too hot for your comfort, there are ways to make the cooling fans come on earlier. With the cooling fans running, it won't get that hot.
Easiest way to force the cooling fans on, is to turn on the A/C. This will also cause the cooling fan (or fans depending on year) to run.
The C4 is one car that actually runs cooling with he A/C running.

 

This is some great information....never heard of this being done..

I can't help but wonder what plugged it internally....would a normal flush been able to remove the clogs..

Are you the only one to have done this???

 

Good stuff RollaMo and TwisterUp. Now that I think about it during last nights trial, the analog gauge never went in to shaded zone. In fact after the fans turned on the analog retraced back to hash mark before the 265*. This was while the car was sitting. I think if I was driving the gauge would read even lower. Normally with the AC on the guage reads in the midldle. I am going to leave the AC off and pay attention to both gauges.
I think you both are on the mark. I thank you for providing supporting information and filtering the muddy waters! A toast to you both

 

Man this is EXACTLY what is happening to me. Thanks everyone for all your replies and taking a little worry out of my head

 

Yeah excellent explanation, but why would GM in their wisdom install a POS analog gauge that is not linear compared to the other analog gauges for oil pressure, voltage, etc?

 

The digital readout is from the Coolant Temp Sensor - the ECM uses that for fuel delivery and if it was skewed, it would either run too lean or too rich. You can verify a couple of ways: 1. Hookup a scanner to monitor Block Learn or Long Term Fuel Delivery vs. The CTS signal. 2. Monitor the signal starting with the engine cold - it should be about ambient and close to the Air Intake Sensor Temperature. Start it up and it should rise to the thermostat; fall back a few degrees and then rise to the threshold for main fan operation. 3. Waste 12 bucks on a new one and simply plug it into the harness - should be the same or real close to the installed Sensor on your Scanner.

As to your analog gage - a quick test is to unplug it and with the wire open, that should be Lo or the Coldest Temp the gage is capable of displaying. Then ground the signal wire and it should swing to Max.

 

For what it's worth, the FSM refers to both sensors for the analog & digital gauges as CTS.