Looking at the temp gage fix page at fierosails, it says to swap the 2 wires at the connector (of a stock 2.8), and 2 at the instrument cluster. The instrument cluster should be the same, but what 2 wires need to be swapped, if any, for the 3 wire coolant temp sensor for a 3800 swap, to prevent the temp needle from pegging? From what I've researched, the wire colors are yellow, green, and black, and yellow goes to the PCM, green goes to the gauge, and black is ground. (1998 grand prix 3800 s/c in an '86 GT 5 speed)
Kind of more for me just to have it written down, but...
On the stock C500: C2 = temp gauge, and D3 = temp light.
3800 swap C500: C2 = temp light (green wire from the PCM), and D3 = temp gauge (green wire of the 3 wire CTS). Then swap the 2 wires at the instrument panel, and this will prevent the temp gauge from pegging, and allow the temp light to light up in bulb test.
Before I do this, I wanted to make sure my temp gauge is working correctly. It does peg on start. I ground the green wire and the gauge pegs. I ground the yellow wire and the idiot light comes on. However, I do not get any reading on the temp gauge. I installed a new thermostat and made sure the coolant level is correct. The needle just hangs out to the left. I measured the CTS with an ohmmeter and read about 2.3k ohms from green to case. I read open from yellow to case and black to case. It reads about 2.6k ohms from black to yellow, and open from green to yellow, and black to yellow. Is this a bad CTS or is my temp gauge just that far out of calibration?
I have a question as well on the temp sensor wiring. Mine is a 2 wire sensor , yellow and black wires. No green and on the C500 I have C2 not connected. Do i need to change the sensor or do I splice into the yellow? Also do I have to do the swap of wires at the insterment panel?
I have read this thread and a few others, but still not sure how to determine the accuracy (of lack thereof) of my coolant temp gauge (CTG). The issue is that the gauge doesn't go very high. The car is a 1986 GT with a 3800SC from a 1997 Buick. The engine has the three wire sensor with yellow, green and black wires in the harness to the sensor. Here's what I've got: - with the ignition key off the CTG needle points to the coolant symbol at the upper left of the gauge. - at key on the needle jumps, but only to just below the 100 degree mark ... it does not bounce to the right and then settle at 100 degrees. - after the engine warms up the needle will point to no more than about 130 degrees. - the coolant fan does cycle off and on. - I used a laser thermometer on the radiator and a few hoses once and the temps were much higher than 130 degrees ... 190 degrees? It was a while ago, but the temp seemed reasonable.
My question is what steps should I take to diagnose this concern? I could try grounding the green wire (per this thread an others). If I do this, and the CTG pegs, does that point to the CTS being out of range? I bought this car with the 3800SC install already done by a PO so I don't have any knowledge of what might have been done. All the other wiring seems to be functioning properly and the gauge does move, but not much, so I tend to think that the issue is with the gauge or the CTS.
Choice one - Using a OBD2 scanner, warm up the engine till the OBD2 scanner shows the engine is in the mid temp operating range and 'flick' the needle to the correct position. (see the link above). When I fixed mine, I found that the needle moved the reverse of what I thought the 'flick' would do.
Choice two - Again using the link above purchase the correct resistance resistor from Radio Shack and insert one end of the resistor into the green wire (center ish) of the CTS socket. Ground the other end. Now with the key on 'flick' the needle into the proper position.
---- Second thought - I think I would just get the 150 ohm resistor from Radio Shack and set it for the 220 deg mark.
---- Third thing to add - Since the gauge IS moving and looks like it works, but it works off, that indicates to me that the wiring is correct the sender at least looks like it is working, again with the exception that the gauge is off (common problem on Fieros)
[This message has been edited by phonedawgz (edited 07-26-2013).]
phonedawgz, Your suggestions are heading me in the right direction. I don't have an OBD2 scan tool (perhaps I need to get one), so I picked up the Radio Shack 150 ohm resistors you recommended. After warming up, the resistor made the gauge needle point mid way between the 100 degree and 220 degree marks (160 degrees?). I need to move the gauge needle so that it points to the 220 degree mark with the 150 ohm resistor between the connector green wire and ground. The Fiero Sails article the writer states that he simply "flicked" the needle until it pointed to where he wanted it to point. Any other thoughts regarding how to adjust the needle other than "flicking" it?
I was able to pull off the gauge needle and reposition it to the gauge setting that I needed. I was concerned about pulling the needle for fear of damaging the gauge, but it didn't put up much of a fight. Pushed it back on and it's now pointing where it should.