It doesn't rise even a tiny bit even after long driving? Then it's
probably the gauge sender in the head.
The sender unit is a single-wire thingie immediately to the rear of the
heater hose outlet in the head under the distributor. It has a round
connector with a yellow/green wire going to it. (Do not confuse this
with the ECU temp sensor, which is larger, has two wires and is
rearwards of the gauge sender!)
Remove the connector and perform these checks:
1) With the engine cold, resistance between the sender's center pin and
a ground should be at least 142 ohms.
2) With engine fully warm (at least fifteen-minute drive), resistance
between the sender's center pin and a ground should be 49 to 32 ohms.
Also check for broken and/or disconnected wires. A car this old can be a
real question mark when it comes to wiring integrity.
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