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Why you NEED an GOOD temp gauge

2

2DRTURBO

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I installed an auxiliary ISSPRO water temp gauge in my truck. Some people thought it was stupid and asked my what the point was considering there is a factory gauge that does the same thing. Well for one thing, I live in the US, but my truck has the non-US instruments so its nice to have the "American" temp instead of the temp the rest of the world uses..... BUT.... seriously, this will be an eye opener for you. Look at this first picture:

issprogauge.jpg

So that looks good, right? The truck after a good hard run on a hot summer day is at 190 degress, just where it should be.

Now, if you do the math 190 degrees farenheit is about 88 degrees Celcius. BUT, look at what my factory gauge is actually showing:

factorygauge.jpg

Looks like about 65 or MAYBE 70 degrees Celcius right? Grossly under the true temp. Very misleading.... So basically this gauge is worthless in giving me an accurate idea of my actual coolant temp. Not good on a 6.5 considering how sensitive these engines are to heat related issues.

I'm not sure if the American farenheit gauges are any more accurate, but my guess is they probably aren't. I believe they are the same gauge just with different numbers printed on the face, but the same "scale"

Now, one more element to the equation: I have the sensor for the ISSPRO gauge mounted on the BACK of the engine in the rear crossover plate on the passenger side by CYL #8 which is believed to be the hottest part of the engine. So this may also explain the discrepency. But either way you look at it, I think this shows what a poor representation the factory gauge can give you (UNDER ESTIMATE) of the actual temps you are running. Although you could feel "comfortable" at 205-220 maximum on the factory gauge, you may in actuality be running quite a bit hotter seriously risking the health of your motor. Just food for thought.
 
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Want to have some fun? Cross-wire the gauges... run the factory one off the new sensor, and vice-versa. THEN see what they read...

I changed out the sensor in my dash gauge (which was correctly calibrated in celcius, just like yours :D) and it made a big difference. Sensors can wear over time; an infrared gun is a great tool for checking!
 
I installed an auxiliary temp gauge and put the sensor in the exact same place as you did. Mine typically read lower degrees Fahrenheit than the stock gauge most of the time. If I was on a very long drive the temps would slowly come close to matching, but still be lower on the aux gauge. If I was towing the aux gauge would eventually go up even, and sometimes over what the stock gauge showed when I was in a long uphill climb.

There is one caveat though. The aux gauge is a Glowshift and due to problems unknown it no longer works. That is not the only Glowshift gauge that is no longer working. Needless to say, I no longer put full trust in the other Glowshift gauges.

Don
 
Interesting, I suppose my factory sensor could be weak and that could explain part or all of the reason for the big difference. I suppose one of the main things to be garnered from my observations are to make sure your sensor is good if you are relying on just the factory gauge....
 
Where are you picking up the temp from? Passenger head runs hotter than the driver's side...
 
WarWagon said:
Where are you picking up the temp from? Passenger head runs hotter than the driver's side...
Click to expand...

I have the sensor mounted in the passenger side head in the rear cross over block off plate. Yes, I was always under the impression that the pass side ran hotter and that's why I put the sensor there.... I was surprised to read handcannons comment that his pass side on his truck would read lower...
 
If my experience is anything to go by, we probably have to put the sensor in a pot of water with a thermometer and bring it to a boil, watching the gauge to calibrate it. It's important to watch the gauge temp, but if that temp reading is inaccurate...
 
EVERY 94 and older cluster I have seen is off that much or more. My 95 is fairly close, if anythiung it tends to read a touch higher than actual. Something about the older style clusters seem to read low.
 
My 94 was reading 160 with a 180 Tstat and holding steady under light load. I went to Autozone, CarQuest and NAPA, measured the resistance at room temp on all the different senders that they had. Lots of variation. BTW, it is called a "switch" not a sender--has one pin not two, mounted to front of driver side head. Anyway, I measured the existing one and picked one that would read higher by resistance and put it in. I guessed right--now the cluster gauge reads between 180 and 185. While I was at it I checked the other sensors against the chart and found the IAT to be wrong so I replaced it at the same time--fuel mileage went up 2 MPG.
 
Be wary of trusting teh stock guages temp scaling as well. if you notice the diesel temp guage starts at 160 whereas teh gasser starts at 100, yet the both use teh same stepper motors for the guage and same sending units. Up to about 180 GM PURPOSELY mis scaled the actual guage numbers to make you think it was warmer than it actually is so peopel wouldn't freak out by how long they stayed cold.
 
Slug, Sender is pretty cheap. The resistance does not match the chart for the IAT and CT used for the ECM tho. I only care about the center of the scale---like where it shows it's too hot. Have noticed these have alot of Tstat bypass and warm up pretty slow, mine seems worse with the heater on.
 
How hard is it to fix? Do you need to rip apart the cluster? I cant remember if i replaced that sensor when i rebuilt me engine
 
I don't have a diagram of the cluster but I think these are like most---just an analog gauge with sender to ground. May have scaling resistors. Sender changes resistance with temp--changing the gauge reading. Per post 9 I found senders varied in resistance at the same temp. If your gauge reads low you need to find a sender that has a lower resistance at the same temp so the gauge reads higher. It is possible to add a resistor to ground, across the sender,--put the sender in hot water take it to maybe 180, measure the resistance, start with a resistor 10% of what you measure. See what the gauge reads--if still low reduce the resistor value in steps.
 
I use a ScanGaugeII to monitor my coolant temps, and what the PCM reports is typically higher than the stock gauge.
 
Two reasons for them to be different, the ecm reads a different sender, the sender is in a different place. The gauge sender does not affect ecm operation.
 
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