Lights / temp gage

Gotta love that wiring . . .
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JimmyO1242000
Posts: 20
Joined: Tue May 22, 2018 4:07 pm
Your car is a: 1980 Spider 2000

Lights / temp gage

Post by JimmyO1242000 »

Soooo

Just rebuilt my entire cooling system. Radiator, therm, waterpump, sensors, fan switch, etc...
Tediously meticulously bled over several days. On the one hand Temp rises and drops fan engages at proper temp.
When I flip my light switch on, my temp starts to climb, hasnt gotten into the danger zone, but idle @ 230-240, drops to 210 ish running.
Lights off , hottest idle @ 210 running @ 185
What the smoke is going on and why so much fluctuation in temp within normal range?

Jimmyo
DRUMMOND
Patron 2018
Patron 2018
Posts: 443
Joined: Thu Oct 20, 2011 11:11 pm
Your car is a: Fiat Spyder 2000 1980 Pininfarina

Re: Lights / temp gage

Post by DRUMMOND »

might want to check you alternator
What charge is it putting out at idle?
sounds like a high resistance.
Check alt bearings see if it moves easily by hand
check belt is not too tight etc.
raysorm
Posts: 13
Joined: Fri Feb 16, 2018 1:12 pm
Your car is a: 1981 fiat 124 2000
Location: San Antonio TX

Re: Lights / temp gage

Post by raysorm »

yea alternator
DieselSpider
Posts: 2130
Joined: Wed Dec 24, 2014 10:21 pm
Your car is a: 1978 124 Spider with Isuzu Turbo Diesel

Re: Lights / temp gage

Post by DieselSpider »

You may want to check the tension on the alternator belt before going too far down any other path. A belt that is not tightened correctly is going to slip under load.
spider2081
Patron 2024
Patron 2024
Posts: 3015
Joined: Fri Jan 27, 2006 11:45 pm
Your car is a: 1981 Spider 2000
Location: Wallingford,CT

Re: Lights / temp gage

Post by spider2081 »

The dash light bulb in the coolant temperature gauge connects to the case of the gauge as does the instruments ground. If there is any issues with these connections the lights power can cause the temp needle to indicate a higher than actual temperature. If you remove the dash bulb from the temp gauge does the problem occur?
The dash light bulb socket has only a power wire going to it. I soldered a wire to the other terminal in the bulb socket and grounded it to the dash grounding pod above the ignition switch. The needle still moves when the lights are on but now less that a needle width.
A few people have reported a similar issue with the "over temp switch" in the head. They can cause the temperature gauge needle to display a temperature higher that actual.
Hope this helps
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OttawaTom
Posts: 43
Joined: Fri Sep 16, 2016 7:49 am
Your car is a: 1976 Fiat 124 Spider
Location: Ottawa, ON

Re: Lights / temp gage

Post by OttawaTom »

Also check the engine ground.

I had a similar issue caused by poor grounding of the engine block. When the lights are on, they cause the current from the alternator to increase (to compensate for the added load or the lights). If there's a bad ground, then the ground of the sensor in the block is at a different voltage to the ground of the gauge in the instrument panel, which can cause a bad reading.

Good luck, and report back to let us know what was the cause.
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