Cylinder Head Temp Gauge - 64 Spyder

All Models and Years
Mr.G
Posts: 19
Joined: Thu Oct 06, 2016 2:08 pm

Cylinder Head Temp Gauge - 64 Spyder

Post by Mr.G »

Where exactly would I find the thermister wire that is connected to the engine ?
dave t
Posts: 138
Joined: Thu Apr 20, 2017 7:16 pm

Re: Cylinder Head Temp Gauge - 64 Spyder

Post by dave t »

Under cylinder #3 right center. Then runs to a plug in the rear of the engine harness by the coil wire.

Sent from my SM-G930V using Corvair Forum mobile app

User avatar
bbodie52
Corvair of the Month
Corvair of the Month
Posts: 11872
Joined: Mon Aug 06, 2012 12:33 pm
Location: Lake Chatuge Hayesville, NC
Contact:

Re: Cylinder Head Temp Gauge - 64 Spyder

Post by bbodie52 »

dave t wrote:Sun May 21, 2017 4:02 pm

Under cylinder #3 right center. Then runs to a plug in the rear of the engine harness by the coil wire.
The sensor that is mounted in the right cylinder head is a cylinder head temperature unit, but it is a simple switch that only provides a ground if the engine reaches a temperature that is high enough to be considered to be an overheat condition. It shares a wiring harness that is connected to the oil pressure sending unit switch which is located just to the right of the generator. A ground on either one of the switches will cause the TEMP/PRES warning light to illuminate. The oil pressure warning light switch defaults in a "closed" condition (when there is no oil pressure). This provides a ground before starting the engine to test the warning light when the key is turned on, but before the engine has been started. When the engine starts and oil pressure reaches the warning switch, the switch opens which removes the ground and turns the oil pressure warning light off. The temperature switch in the right cylinder head is never closed unless the engine overheats. I have been driving Corvairs since the 1960s and I've yet to see that warning light come on because of an overheat condition.

The cylinder head temperature gauge that is found in the Corvair Spyder (1962-1964) or the Corvair Corsa (1965-1966) is connected via a single wire to the thermistor, which is located near the underside front of the left cylinder head. The thermistor looks like a small spark plug. It is a variable resistor that changes resistance value as engine temperature changes. While the switch on the right side is a simple ON/OFF switch that controls a warning light, the thermistor is an analog device that varies resistance along with head temperature changes, which is reflected as a temperature reading on the gauge.

Left-click each image with your mouse to enlarge the image for better viewing…
1964 Combined Passenger Compartment & Engine Compartment Wiring Diagram
1964 Combined Passenger Compartment & Engine Compartment Wiring Diagram
1964 Spyder Temp Gauge Detail
1964 Spyder Temp Gauge Detail
Spyder Wiring Differences
Spyder Wiring Differences
The complex warning light arrangement in the above diagram uses a silicon rectifier (diode) to prevent the warning buzzer from coming on when the warning light is illuminated by the oil pressure warning switch. The audible warning buzzer only comes on if the engine overheats and closes the temperature switch, which would illuminate the warning light AND sound the buzzer.

Spyder Instrument Cluster (4).jpg
Spyder Instrument Cluster (6).jpg
Thermistor Location (Left Cylinder Head)
Thermistor Location (Left Cylinder Head)
Wiring Circuit Color Code.jpg
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible
dave t
Posts: 138
Joined: Thu Apr 20, 2017 7:16 pm

Re: Cylinder Head Temp Gauge - 64 Spyder

Post by dave t »

BBODIE52 is correct. My mistake. The sender on the right is for the light. The thermister in the left head is for the gauge. My bad. Sorry

Sent from my SM-G930V using Corvair Forum mobile app

66vairguy
Posts: 4531
Joined: Tue Dec 21, 2010 3:44 pm

Re: Cylinder Head Temp Gauge - 64 Spyder

Post by 66vairguy »

Brad did a great job of covering the circuit and component location.

Note that the Spyder temperature gauges weren't as accurate as the LM Corsa guage and the thermistor drifts with age. Bottom line - figure out where the needle is during normal operation and if it start going up - beware. By the time the overtemp buzzer and light come on the engine is overheated to the point damage may occur.

Always make sure the FAN/GEN warning indicator illuminates when you turn the key on BEFORE starting.
Post Reply

Return to “Ask your Mechanical Questions here”