Temperature gauge and sensors

Keep it on topic, it will make it easier to find what you need.
Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Temperature gauge and sensors

Postby Gatorman » Sat Jan 27, 2018 8:12 pm

Cold beer for whoever figures this out!
I’m having some odd temperature gauge behavior on my 1982 FI, and a search of every gauge and sensor related post didn’t give me any clear answers. Fan switch is new, heater core bypassed and system has been burped with Mark’s throttle body heater.
Gauge was reading about 190 driving but a good bit higher than actual when idling at operating temperature (fan cycles on at about 230-plus indicated on gauge whille IR readings appeared normal.) I disconnected the high temp switch and gauge dropped quite a bit but still reading high (210-220). Installed new sensors, cut out some brittle wiring and replaced spade connectors, but now it reads very low (halfway between 120-190 when fan comes on). Also, now if I disconnect the high temp switch the gauge dies altogether. (First time it went right to 190, then bounced around before it died, but now it just dies). Temperature gauge resistor appears OK and I cleaned the ends before reinstalling, but gauge behaves the same.
Finally, another mystery to me - there appears to be a very small resistor soldered into the high temperature switch wiring, just ahead of the sensor. Never saw anything similar mentioned so maybe it was another one of my late father’s jury rigs, but not sure what the point was since the resistor under the dash appears to be OK.

Any clues?
Thanks

User avatar
RRoller123
Patron 2020
Patron 2020
Posts: 8179
Joined: Sun Nov 13, 2011 2:04 pm
Your car is a: 1980 FI SPIDER 2000
Location: SAGAMORE BEACH, MA USA

Re: Temperature gauge and sensors

Postby RRoller123 » Sat Jan 27, 2018 8:44 pm

That resistor may be a telltale. Possibly not original gauge? And the resistor was added to "calibrate" it?
'80 FI Spider 2000
'74 and '79 X1/9 (past)
'75 BMW R75/6
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/STD BED
2002 Edgewater 175CC 80HP 4-Stroke Yamaha
2003 Jaguar XK8
2003 Jaguar XKR
2021 Jayco 22RB
2019 Bianchi Torino Bicycle

Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Re: Temperature gauge and sensors

Postby Gatorman » Sat Jan 27, 2018 8:53 pm

RRoller123 wrote:That resistor may be a telltale. Possibly not original gauge? And the resistor was added to "calibrate" it?


I suspected that, assuming it wasn’t original, but wanted to make sure it wasn’t part of stock system before I try running without it. Would gauge read lower with more resistance?

User avatar
RRoller123
Patron 2020
Patron 2020
Posts: 8179
Joined: Sun Nov 13, 2011 2:04 pm
Your car is a: 1980 FI SPIDER 2000
Location: SAGAMORE BEACH, MA USA

Re: Temperature gauge and sensors

Postby RRoller123 » Sun Jan 28, 2018 9:07 am

Don't know, that depends upon its design. Someone here I am sure knows if the tank float increases or decreases resistance as the tank is filled.
'80 FI Spider 2000
'74 and '79 X1/9 (past)
'75 BMW R75/6
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/STD BED
2002 Edgewater 175CC 80HP 4-Stroke Yamaha
2003 Jaguar XK8
2003 Jaguar XKR
2021 Jayco 22RB
2019 Bianchi Torino Bicycle

Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Re: Temperature gauge and sensors

Postby Gatorman » Sun Jan 28, 2018 10:35 am

RRoller123 wrote:Don't know, that depends upon its design. Someone here I am sure knows if the tank float increases or decreases resistance as the tank is filled.


Just to clarify - we’re talking about temperature gauge not fuel gauge

Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Re: Temperature gauge and sensors

Postby Gatorman » Sun Jan 28, 2018 12:16 pm

Gatorman wrote:
RRoller123 wrote:That resistor may be a telltale. Possibly not original gauge? And the resistor was added to "calibrate" it?


I suspected that, assuming it wasn’t original, but wanted to make sure it wasn’t part of stock system before I try running without it. Would gauge read lower with more resistance?


Mystery (mostly) solved - cold beer for me! 8)
Removed the resistor and now fan kicks on at the 190 zero. Still don’t understand why gauge died when I removed the high temperature connector (or why gauge reads higher with apparently less resistance in the circuit) but I guess I won’t worry about that.

User avatar
RRoller123
Patron 2020
Patron 2020
Posts: 8179
Joined: Sun Nov 13, 2011 2:04 pm
Your car is a: 1980 FI SPIDER 2000
Location: SAGAMORE BEACH, MA USA

Re: Temperature gauge and sensors

Postby RRoller123 » Sun Jan 28, 2018 5:55 pm

ooops. my mistake, need to read these more closely.
'80 FI Spider 2000
'74 and '79 X1/9 (past)
'75 BMW R75/6
2011 Chevy Malibu (daily driver)
2010 Chevy Silverado 2500HD Ext Cab 4WD/STD BED
2002 Edgewater 175CC 80HP 4-Stroke Yamaha
2003 Jaguar XK8
2003 Jaguar XKR
2021 Jayco 22RB
2019 Bianchi Torino Bicycle

gchocevar
Posts: 108
Joined: Tue Oct 21, 2008 9:40 pm
Your car is a: 1979 Pininfarina 2000
Location: Cleveland Ohio USA

Re: Temperature gauge and sensors

Postby gchocevar » Sun Jan 28, 2018 7:19 pm

Gatorman,

I had the same problem and the same question on my 79. When I disconnected the hi-temp switch the gauge read normally. I traced through the 79 schematic and found that the hi-temp switch shorts out the gauge across the dropping resistor in series with the switch.

I concluded that the intent was for the gauge to work normally, but if the high temperature switch is made, it pegs the temperature gauge. I also found out that my switch was bad. I added a a Hi-temp warning light and wired it to the switch, keep it completely out of the gauge circuit.

Either you have a bad switch also, or a pocket of air in the head causing the gauge to peg.

Greg

Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Re: Temperature gauge and sensors

Postby Gatorman » Sun Jan 28, 2018 9:50 pm

RRoller123 wrote:ooops. my mistake, need to read these more closely.


No worries - thanks RRoller. You were on the right track with the resistor.

Gatorman
Posts: 20
Joined: Sun Sep 18, 2016 11:17 pm
Your car is a: 1982 Spider
Location: Merritt Island, FL

Re: Temperature gauge and sensors

Postby Gatorman » Sun Jan 28, 2018 10:01 pm

gchocevar wrote:Gatorman,

I had the same problem and the same question on my 79. When I disconnected the hi-temp switch the gauge read normally. I traced through the 79 schematic and found that the hi-temp switch shorts out the gauge across the dropping resistor in series with the switch.

I concluded that the intent was for the gauge to work normally, but if the high temperature switch is made, it pegs the temperature gauge. I also found out that my switch was bad. I added a a Hi-temp warning light and wired it to the switch, keep it completely out of the gauge circuit.

Either you have a bad switch also, or a pocket of air in the head causing the gauge to peg.

Greg


Thanks Greg - I knew how it was supposed to work and it never pegged, just read hotter than it should. I suspected a bad high temp sensor, but the odd behavior continued after I replaced both sensors. I have it sorted now that I’ve removed the extra resistor.


Return to “Engine and Tuning”

Who is online

Users browsing this forum: No registered users and 16 guests