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Coolant Temp Gage Question 3800 s/c by bomluuk
Started on: 12-11-2012 03:11 PM
Replies: 15 (1290 views)
Last post by: gtoformula on 07-31-2013 11:15 AM
bomluuk
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Report this Post12-11-2012 03:11 PM Click Here to See the Profile for bomluukSend a Private Message to bomluukEdit/Delete MessageReply w/QuoteDirect Link to This Post
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)
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phonedawgz
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Report this Post12-11-2012 04:00 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
On a 3800 swap, the green wire of the 3 wire CTS is for the gauge.

There is also a green wire from the PCM for the TEMP light.

Instead of connecting them to the correct C500 as per the factory, just swap where the two wires hook up.

-----

If the 3800 harness is one of mine, I have already wired the engine harness with the swap unless specified not to on the build sheet. You then only have to do the swap at the dash.

[This message has been edited by phonedawgz (edited 12-11-2012).]

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bomluuk
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Report this Post12-11-2012 05:50 PM Click Here to See the Profile for bomluukSend a Private Message to bomluukEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.

Correct?
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phonedawgz
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Report this Post12-11-2012 09:04 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
Correct
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bomluuk
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Report this Post12-13-2012 03:54 PM Click Here to See the Profile for bomluukSend a Private Message to bomluukEdit/Delete MessageReply w/QuoteDirect Link to This Post
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?
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bomluuk
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Report this Post12-14-2012 11:16 AM Click Here to See the Profile for bomluukSend a Private Message to bomluukEdit/Delete MessageReply w/QuoteDirect Link to This Post
Based on the looks of the CTS, I decided to get a new one. No difference
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phonedawgz
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Report this Post12-14-2012 11:25 AM 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
It sounds like your CTS is working fine. Your gauge will get off over time from the pegging issue.

Follow the instructions here to reset your gauge - http://www.fierosails.com/tempgage.html
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Report this Post12-21-2012 04:02 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
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?

Thanks in advance for any help.

------------------
Red 1988 GT 5 speed
Poly all around, Koni's & Lowered
LQ1 powered
http://s733.photobucket.com/albums/ww339/CC_Rider/

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Jncomutt
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Report this Post12-21-2012 06:17 PM Click Here to See the Profile for JncomuttClick Here to Email JncomuttSend a Private Message to JncomuttEdit/Delete MessageReply w/QuoteDirect Link to This Post
You need the 3 wire sending unit.
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CC Rider
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Report this Post12-21-2012 06:32 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks!
So I have a old series ll and this series lll and both have only 2 wires?
What car do I get the 3 wire from?
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Report this Post12-21-2012 07:45 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
DP

[This message has been edited by CC Rider (edited 12-21-2012).]

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Report this Post12-21-2012 09:49 PM Click Here to See the Profile for CC RiderClick Here to Email CC RiderSend a Private Message to CC RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
Found it
GM 10096181
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gtoformula
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Report this Post07-26-2013 04:43 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
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.
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phonedawgz
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Report this Post07-26-2013 09:48 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
Most likely the needle has slipped on the shaft of the gauge. This can be 'fixed' somewhat easily.

http://www.fierosails.com/tempgage.html

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.

http://www.radioshack.com/p...3FitemId%3d2994582%2 6utm_source%3dGoogle%26utm_medium%3dPPC%26utm_term%3d2710010%26utm_content%3dExact%26utm_campaign%3dPLA%7d&cagpspn=pla&gclid=CNDoxY7IzrgCFQieKgod9koAAA&gclsrc=ds.ds

----
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).]

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gtoformula
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Report this Post07-28-2013 09:10 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
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?
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gtoformula
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Report this Post07-31-2013 11:15 AM 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
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.
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