SeeFourSix

I know I can use the manual method with a switch and use the temp probe in the radiator but I can't seem to find a chip that ONLY lowers the temp in which fans come on. I don't want all the other BS that comes with the cheapo chips. I have a 91 and it's my understanding I can use a 'piggyback chip'. When my HVAC temp reading shows 95*C, my analog gauge is pegged at 260*F. Not cool. It has a new switch too. Maybe it's the wrong one? At 86*C, the analog gauge on cluster is just past halfway.. Just doesn't seem right.. Better suggestions?

vetteoz

Custom tune only
http://pcmforless.com/index.php?opti...d=91&Itemid=29

Try this guy on 3rd gen
http://www.thirdgen.org/techboard/po...781-post4.html

c4cruiser

Sounds more like a coolant temp sensor or a cooling system issue. Have you verified that the coolant temp is actually at 260F? Is there any indication of boiling over? Is coolant flowing into the expansion tank?

Will the temps come down and stay steady at freeway speeds? Or do the temps climb right up to that temps after engine start and stay there?

With the cooling system in good condition, normal coolant temps should be around 180 to 195; in hot weather or heavy stop and go traffic you may see 205-220. Turning the A/C on can help to drop temps too.

RollaMo-LT4

OP, please take a good look at your gauge when you think the temp is "pegged at 260".
Is it really pegged all the way over?

I ask this, because 260 is the max reading and the needle would need to actually be pegged against the stop.
If you look closely at the gauge, you'll see a small "shaded area" at the end of the scale.
If the needle isn't actually into that shaded area, your temps are not really at 260.

Also keep in mind that gauge does not have a linear display.
That gauge has caused more grief and misunderstanding than any gauge GM has ever put in a car.

I am not sure if your '91 has a digital temp gauge or not, but if it does what is the reading on that gauge?

FASTAZU

If I'm not mistaken you can read coolant temp thru the AC head unit as long as its not manual air.

Your AC unit actually has the ability to tell you what the coolant temperature is as well. NOTE: it's in Celsius! (to convert to Fahrenheit, multiply by 1.8 and add 32)

Steps to check: hold the fan up and fan down arrows until "00" is displayed on the AC temperature display. Press the center fan button. Scroll to "16." Press the center fan button again. There's your temperature, digitally, and more accurately than the analog gauge.

1990 - 1996: HVAC Diagnostic Codes

On 1990 to 1996 Corvettes equipped with RPO C68 (electronic climate control), it is possible to read the HVAC system diagnostic codes from the climate control panel on the dashboard.


1. To enter the diagnostic mode, press the fan up and down arrow buttons at the same time until -00 appears on the digital readout.

2. One you have entered the diagnostic mode, you can scroll through the various parameters by using the up and down fan buttons.

3. To view the value for a particular parameter, press the "AUTO" fan button.


Note: If you see a "-" next to a parameter value (example: "-105"), you must add "100" to that value to obtain the correct value for that parameter. Therefore, the correct reading would be 205 for this example.
Parameter Description Values
0 System Faults
(one of these will be set if your air conditioning controls have an LED flashing) 00=No Faults
01= Temp Door Motor Circuit Fault
02= Temp Door Motor Circuit Fault
03 = Ambient Sensor Open
04 = Ambient Sensor Short
05 = In-Vehicle Temp Sensor Open
06 = In-Vehicle Temp Sensor Short
07 = Solar Load Sensor Open
08 = Solar Load Sensor Short
09 = Low Freon Detected
10 = UART Failure
1 Temp Setting 60F to 90F
2 In-Car Temp Sensor 10 = HOT -130 = 230 = COLD
3 Outside Temp Sensor 10 = HOT -130 = 230 = COLD
4 Sun Load Sensor Max light Max Dark
L98 38 183
LT5 115 -110 = 210
5 Ignition System Voltage 0 = 9 Volts -155 = 255 = 16 V
6 Engine Speed (RPM divided by 25)
7 Vehicle Speed
9 A/C System Mode 00 = OFF
01 = Re-Circulation
02 = A/C
03 = Bi-Level
04 = Heater
06 = Defrost
07 = Vent
10 = Manual Re-Circulation
10 Blower PWM 0 = 0 Volts 128 = 14 Volts
11 Program Number 00 = COLD -155 = 255 = HOT
12 Mix Number -155 = 255 = COLD 00 = COLD
16 Coolant Temperature In degrees C
17 Solar Correction 114 = Max light 128 = max dark
30 Stored Full Hot Value 0 to 50
31 Temp Door Travel Range 100 to 200
34 Temp Door Position Requested 00=Full HOT -153=253=Full COLD
35 Compressor On Time 0.1 second increments
36 Number Of Times Below Critical Time
37 Software Version Number

SeeFourSix

Thanks for the replies. Yes, in my original post I mentioned that when I compare my HVAC (or AC head unit) coolant reading [in Celcius] with my analog cluster gauge, the cluster gauge reads much higher. I did exaggerate when I said it's pegged. It's actually just barely before the shaded area. I guarantee you when at 10x*C reading from the AC unit, the cluster analog gauge would be pegged, or at least past the shaded area & on the 260*F mark. I do realize the two readings are from 2 different sensors but still... 100*C = 212*F My fan doesn't even cut on until 228*F and by then the gauge would literally be pegged, if not before. The cluster sensor is new. ECM sensor is not. It worries me to see my cluster temp gauge pegged, even though the actual temp may be a bit lower. but how do I even know that? What's to say the ECM sensor is off and the new sensor is correct?

While cruising, the temp is between 100 & 260 and the AC unit reads 85-88*C. Awesome. I'm good with that. As long as the AC is on the temps don't really get past 93*C or so. I'm ok with that. But I really don't want to ride with the AC on just to cool the engine. I'd rather my fans come on at a, what I would call, 'normal' temp. Coolant does not boil over and has no other indication of running hot. I do not know how to verify the actual temp without a thermal gun. FYI, I have a new 180* t-stat, new hoses, cleaned radiator (inside & fins), and fresh coolant. Sitting at a red light with the top off and watching the temp climb is worrisome! I actually don't drive the vette as much as I would bc of that.

Thanks for the links vetteoz. I was actually going to use the first guy when I swapped a 4.8L out for a 6.0L in a Z71.

RollaMo-LT4

Probably not.


Unless you see that needle actually into the shaded area, stop worrying about your temp.
GM should have never put that almost useless gauge in the C4.
Your fan coming on at approx. 228°F is normal and where the factory set it.

They are coming on at a "normal temp".
Its just that what you consider is normal is different than the factory designed.

Sounds like your car is performing just as it was designed too.

When moving at any speed over approx. 35 mph, you have plenty of airflow moving across the radiator cooling fins and the temps will remain close to the thermostat setting.
When stopped or moving slowly in stop and go traffic, you have little to no air flow moving across the cooling fins.
The temp will rise up to the fan turn on limit, at which point the fans will begin to cool the temps down a little.
Then the fans will shut off, and the cycle will repeat.

Your car will run all day long like that.

With the proper coolant mix, and pressure cap your coolant boiling point is close to 260°F

Watch that needle on the analog gauge, and there is a very good chance it will not reach into the shaded area.
When stopped for any length of time, it will move all the way close to that shaded area though.

SeeFourSix

Thanks for the reply. I will drive it more with the ac off and see if it climbs to the shaded area. Once while idling in my driveway for a short time, my AC unit read 101 and the cluster gauge was AT the shaded area. I will snap a pic next time it gets there and I'll take note of length of time it took to get there from cruising and what the AC unit reads.

I guess one thing I should mention that weighs heavily in the back of my mind through all of this is the lower radiator hose... I changed it (what a PITA) when I changed all the other cooling system stuff as preventative maintenance and I have never liked how it rides on the tensioner and front unibody brace as it contours from the radiator to the water pump. Makes me feel like it's restricted or collapsing. There was no spring inside the hose & I did not add one. I did re-install the outer sleeve that prevents chaffing though. Just speaking, errr typing outloud.

SeeFourSix

Well I finally got around to getting a picture of the cluster gauge with ac off. This is just in town driving, not sitting for any length of time. My biggest concern is the difference between the cluster gauge and the reading from the ac control. The ac control read 94°C when I took this pic. 94°C = 201.2°F. Gauge looks more like 230-240 to me.. sensor is new. I'd like for my fans to come on before 200°F with ac off.

RollaMo-LT4

You have no way of knowing exactly what temp that analog gauge is reading.
As mentioned earlier, it does not have a linear scale.
The only two numbers on that dial are 100 and 260
Where the needle is showing on your gauge, is about where it should be in normal stop and go traffic.

Unless you see that needle actually move into the "shaded" area of the gauge, your car is not overheating.

Cruisinfanatic

you think that your water temp is 240? Do you think your oil temp is 120?
Ignore the idiot guages

auggy

Sounds like the car may be running a little too hot. The gauges may be ok in which case your focus should be on the cause. Here is a common one and not too hard to fix. Look for air in the system and how to bleed it out. The LT1 runs at 195-205 while moving and up to about 235 in traffic. Not sure about the L98(in the 91) temps and bleeding procedures, but I would think the temps would/should be no higher.

c4cruiser

Is the engine running in this pic? The VOLTS gauge seems to indicate that the engine is off and the key is not in the RUN position..

The coolant temp you see in the Climate Control diagnostic readout is definitely NORMAL for a cooling system in good condition. 201 degrees F. is fine.

Analog gauges are not linear in terms of how they read. For example, if the needle is in the middle of the range (100-260), the actual coolant temp could be right around 160-180. As the needle moves, the indicated temp value will get much higher over a shorter distance. The analog coolant temp gauge worked that same way on my old '92. I always used the digital display to check temps.

One thing you may want to try is to get a separate temp gauge and see what it reads. You can get either an electric gauge or a mechanical gauge. But I'll bet that an aftermarket gauge will read the same as the display in the climate control diagnostic display.

These cars are designed to run at a hotter temp. The extra heat helps with lowering emissions. Everything appears to be fine, there is no need to spend money on a problem that really doesn't exist at this point.

Allentown Ernie

In my 90 coupe I was always worried about the coolent temps in the summer. The other posters are correct that the fans come on at 228 degrees however that can be changed with a chip adapter. I bought mine from TPI parts. I also had the VATS deleted as some owners had trouble with the system as these cars are getting very old. Now my fans come on at 200 and off at 185. My car almost overheated this summer with the air on and stuck in traffic, the coolent bubbled out when my car was in the garage. Now my car fans come on when the gauge is in the middle and off when supposed to. I am very pleased with this computer chip setup.

SeeFourSix

Thanks Allentown Ernie, that is the info I was looking for regarding a chip.

Cruisinfanatic, no, I do not think my oil temp is at 120. The gauge, sensor, or wiring is not functional. My coolant temp gauge however IS functional. And yes, I do believe that the gauge is reading 230-240 in that last pic I posted. I do not, however, believe that my car is actually running at that temp. Hence, my topic of discussion and picture.

c4cruiser, thanks for your reply. yes, I had just cut my car off when I snapped that pic. The temp gauge doesn't move since it's measured by resistance. Maybe someone else could snap a picture of their analog (cluster) gauge, when the ac unit reading is at 94 degrees C. just for comparison... I mean, maybe my new temp sensor is off..

RollaMo-LT4, my point is that if the needle ever did reach the shaded area, that my ac unit would have a reading of about 100 degrees C. Which last time I checked was 212 degrees F... and still a "normal C4 operating temperature". So I reason that one of my temp sensors or gauges is off and I hope it's the analog/cluster gauge. Also, I was not in stop and go traffic when I took that picture, nor was I before that picture. I live in a small town and stop and go traffic is non-existent here.


I do understand the temps that these cars run at, reasons for that, the fact that the analog gauge is not a linear reading, and when the fans are designed to turn on.

My issue is simply the 2 coolant temp gauges having what I would call different readings & that I would like my fans to come on sooner but w/ no additional BS in a chip.