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Temp gauge wiring revisited by rmcmsw
Started on: 08-04-2013 02:52 PM
Replies: 9 (825 views)
Last post by: Spoon on 11-28-2013 08:37 PM
rmcmsw
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Report this Post08-04-2013 02:52 PM Click Here to See the Profile for rmcmswClick Here to Email rmcmswSend a Private Message to rmcmswEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have read the recommended re-wiring of the gauge wires to correct the pegging of the temp gauge needle. One thing the article fails to mention is the color code of the wires when they are in the correct position. I may have already done this mod since I have owned my 86 GT since it was new but after all these years one begins to forget what they have done and not done to their car. In other words, what is the color of the wires on A and B terminal and terminals 11 and 13 after the wires have been moved?

One of the reasons I ask this is that my temp gauge rarely goes above 150 degrees. I have a 195 degree thermostat and a Champion 3-core radiator. I bought and tested the system with the Rodney Dickman temp gauge tester and everything reads like it is suppose to. I have a halve dozen sender units as well as gauges and they all read the same. Turn the ignition key to the run position and it reads 100. The gauge does not peg when starting up. I’m at a loss as to what is wrong. I don’t think the engine is running that cool and the thermostat should raise the water temp to 195 degrees like it is suppose to. I may have not rewired it correctly some decades ago but I don’t want to start taking things apart without the correct wiring colors or it could be something else. Any thoughts will be appreciated.
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phonedawgz
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Report this Post08-04-2013 04:31 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
Does the temp light come on when you turn the key to start? If so then you have the dash wiring swapped per instructions.

What does the engine temp show using a scanner?
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rmcmsw
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Report this Post08-05-2013 10:30 AM Click Here to See the Profile for rmcmswClick Here to Email rmcmswSend a Private Message to rmcmswEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, the temp light comes on when turning the key to start and goes off when the engine starts. I don't have access to a scanner. The gauge usually reads around what would be 150-160 degrees and only rarely has gone past that point. It use to work fine a couple of decades ago but has been this way for about 15 years. Changing thermostats doesn't make any difference.
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fastblack
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Report this Post08-05-2013 01:29 PM Click Here to See the Profile for fastblackSend a Private Message to fastblackEdit/Delete MessageReply w/QuoteDirect Link to This Post
Correct me if I'm wrong but I believe the wire colors changed from year to year and even model to model.

For what it's worth, my car takes a looooooong time to get "warm." I can drive my 20 mile (highway) drive to work and it will only get around 160 or so degrees. It's only on long trips or city driving on a hot day that it gets up to the thermostat temp (200 or so). I always thought it was a bit odd but would rather have it always run on the cool side than the hot.

I'm thinking your gauge has had the fix done and is working properly.
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olejoedad
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Report this Post08-05-2013 05:30 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fastblack:

Correct me if I'm wrong but I believe the wire colors changed from year to year and even model to model.


Correcting you.......the wire colors are the same from year to year and model to model......

The wiring colors are as follows.....after the change on the dash connectors C2 and C3.......

C2-11 should be dark green
C3-13 should be light green

At the sending unit......

Pin A should be dark green
Pin B should be dark green/yellow

Hope this helps....

[This message has been edited by olejoedad (edited 08-05-2013).]

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rmcmsw
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Report this Post11-26-2013 05:04 PM Click Here to See the Profile for rmcmswClick Here to Email rmcmswSend a Private Message to rmcmswEdit/Delete MessageReply w/QuoteDirect Link to This Post
I give up. I am unable to get my temperature gauge to read even close to what the real temperature is. I’ve reversed the wires on the connector (A to B & B to A) that goes to the temp sender unit. I reversed the wires to the printed circuit (11 to 13 & 13 to 11) on the dash; changed the wires on the ignition switch plug on the steering column (G-1) and on the C-500 ( C2 to D3 & D3 to C2) block. I bought a new gauge assembly from the Fiero Store, a new AC Delco 195 degree thermostat (#10192505) and a new Delphi sender unit DHPTS 10051. The gauge still only wants to read approximately 160 degrees before the thermostat opens and then the gauge drops to around 140 degrees before it begins to climb back to around 160 degrees (mid scale).
My dash printed circuit board was delaminating so I went to a salvage yard and found one that was almost new and installed it. No change. So I decided to run new wires all the way from the sender to the dash plugs and still no change after wiring everything according to all the blogs. I bought a laser temperature reader and measuring at the thermostat neck, it will read around 180-185 degrees before the thermostat opens. (It’s a Harbor Freight tester so not the most accurate.)
I do though, have a new Champion 3-core aluminum radiator and new radiator caps on both the radiator and the thermostat neck on the block. At first I thought it was the 3-core radiator but I had the problem before I had to change out the radiator. Also, a friend in Dallas, has the same problem with his GT and everything on it is original. I have three other temperature gauge assemblies and sender units and have tried each of them and they all read within a white line of each other (around mid scale).
Last summer, when it was around 100 degrees, I fired up the engine and let it idle to see how far the old gauge would read and after a half hour, it finally made it to 220 degrees where the radiator fan came on like it is suppose to.
Shouldn’t the thermostat raise the engine temp to where it is suppose to be (195) no matter whether one has a 1, 2, or 3-core radiator?
After I switched the wires around, the temperature indicator light now glows brighter when starting the engine though. The only thing I can think of is to put the wires back to their original position and see what happens. The gauge read where it was suppose to (one to two white lines before 220 on the gauge) for the first 21 years or so this car’s life but it something I have been trying to fix off and on for the last six years.
Looking at the wiring schematic (page 8A-80-0 in the 88 factory service manual), it shows that terminal A is a variable resister and the resistance changes with temperature changes and that is what makes the needle on the gauge move. Terminal B is just a temperature on and off switch that is triggered by a certain temperature. It seems to me that I should change the wires back at least on the sender unit. I also have the Rodney Dickman temperature gauge tester and hooking it up according to his instructions (his instructions are shown with the original wiring) and the gauge reads correctly.
Any thoughts????
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Boostdreamer
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Report this Post11-26-2013 08:46 PM Click Here to See the Profile for BoostdreamerClick Here to Email BoostdreamerSend a Private Message to BoostdreamerEdit/Delete MessageReply w/QuoteDirect Link to This Post
I have a similar situation. My gauge reads about 170*F after full warm up. I have ordered the Stant Superstat 195*F thermostat #45819 and the AC Delco ECM coolant sensor # 213928 from Rock Auto. My gauge will read differently when using other stats. One stat I have makes the gauge read up toward the red overheating zone. I'm not sure I trust any of them. That's why I ordered the new one. I was also going to buy the same China Freight laser thermometer! I figured the money would be better spent on a new stat.

The biggest indicator I have that the engine really IS as cold as the gauge says is my terrible gas mileage. I'm getting about 17 mpg in mixed driving including a large portion of interstate driving. I'm either not getting into "closed loop" or something else is seriously wrong.

What kind of gas mileage are you getting?

Jonathan
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rmcmsw
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Report this Post11-28-2013 12:39 PM Click Here to See the Profile for rmcmswClick Here to Email rmcmswSend a Private Message to rmcmswEdit/Delete MessageReply w/QuoteDirect Link to This Post
Just put in the new gauge, thermostat, and sender unit and rechecked my rewiring and all is correct. The damn gauge still will only go to 160 and then drop back to 140 when the thermostat opens. I have three sender units and they all read the same and I have four temperature/fuel gauges and they all read almost identical; mid-scale (I'm guessing 160 degrees) when fully warmed up. The temperature at the thermostat neck reads 190. I'm out of ideas and give up. I'm going to put the f@#$ing car back together and live with it and spend no more time and money. I've lived with this car since April 1986 and have spent way too much time and money trying to keep it like new and fix GM's mistakes.

The other question answer: I get around 22 to 26 mpg most of the time. I haven't driven it for any long distance for several years. I'm always fixing something and the car is torn apart. Also regarding mpg; the engine is one of the last 3.1 GM built for the 88 GTs and has been further modified; Crane Compu Cam with the Crane valve springs, etc., S/S valves, heads ground out to gasket size, ported and polished. Engine balanced; intake manifolds ground out to gasket size, ported and polished, 60 mm over bored TB, Crane Gold Series 1.5 roller rocker arms, and Fiero Owners of America Headers and no cat. I did have some Crane Gold Series 1.6 roller rockers on it but changed back to the 1.5s.

I love the car and the way it drives but wish I could just get in it and drive it without having something not work right or go wrong. I'm getting to that burn out point.

I've powder coated most of the metal parts on it, installed the Walt Zimmer big brake thing with slotted and drilled rotors, did a body off paint job with 3 extra coats of clear, Mr. Mike's interior, new head-liner, new glass, 17" rims with Goodyear F-1 tires, Koni shocks, Nardi wood-rim steering wheel, 2000 Pontiac stereo with Polk speakers, and the list goes on and on.

I'm just bitching.
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gtoformula
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Report this Post11-28-2013 01:04 PM Click Here to See the Profile for gtoformulaClick Here to Email gtoformulaSend a Private Message to gtoformulaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sounds like a very nice car. You've put a great deal of work into it. Sometimes it helps to just jump in and the drive the thing for a while. After a nice back roads drive you may start to feel differently about your car. Regarding the temp gauge ... I have not done all the work that you have, but have similar issues. My gauge will go up, but not far enough. I've also checked the radiator and thermostat neck with a laser thermometer and know that the gauge is not accurate. I also replaced the temp sending unit. My car has the 3800SC, but temperature is temperature. When I have driven the car long enough to heat up the radiator fan will cycle on and off as I would expect. I'm going to install an aftermarket temp gauge and mount in somewhere like at the bottom of the dash by the driver's side of the radio/HVAC pod. I don't really trust gauges on older cars so at least I'll have a secondary method to check operating temperature.
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Spoon
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Report this Post11-28-2013 08:37 PM Click Here to See the Profile for SpoonSend a Private Message to SpoonEdit/Delete MessageReply w/QuoteDirect Link to This Post
I can't believe it took this long to hear a story like that. I had the same problem back in the 70's after modding a 318 in a 72 Dodge van. All I changed was adding a 4 bbl carb & intake, mild cam , shaved heads and headers. After that the engine would never meet the temp of the t-stat.

This was before cat convertors and ECM's. I wouldn't of cared except in the winter months the heater was only putting out luke warm air. Tried everything and I'd go as far to say that if I put my hand to the tailpipes the exhaust even felt somewhat cool in respect to real exhaust temperatures. I also cooked out the heater core.

Blocking the radiator with cardboard idling made no difference but on the road it did so I made a cardboard thermostat by cutting enough slots in it for the desired effect. Even took it to the Dodge dealer and they said they got the gauge to climb very slightly by removing the fan belt and gave up.

Shaved heads should raise the temp. Carb should make no difference if adjusted correctly. Cam & headers unknown.
Just don't make sense. Never did figure it out.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

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