When removing the temp sensor on a 78 K5 will this cause coolant to run out from the engine block?

[wazzabie]

When removing the temp sensor on a 78 K5 will this cause coolant to run out from the engine block?

I have a temp sensor that is reading 1.2k ohms at cold and 198 ohms at operating temp when the thermostat opens. According to the chart below my sensor is faulty.

For Truck Years: 1974 - 1978

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years: 1979 - 1990

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

 

[76zimmer]

wherever its located, coolant will be in the hole.

 

[dyeager535]

"Easy" method to minimize coolant loss. Small diameter, long vacuum line, couple milk jugs or suitable receptacles. Remove radiator cap, fish hose down as far as it will go, start siphon into receptacles. That'll remove a fair bit of coolant, that you then won't lose to leakage.

Temp sensor is up high enough it shouldn't take much removed, but easy enough to refill so I just suck out all that the hose will pull.

 

[Wes Harden]

Actually since you are only making one hole if you put cellophane under rad cap, then remove the sensor it will create a vacuum and hold the coolant in the head. A little will escape, still need to fast at the exchange.

The 74 to 78 sensor, with ohm reading you want, only comes in 1/2" npt. I think the sensor you have now is for 79 up, and 3/8" npt.
My 77 had same issue. Got a sensor for my year, was 1/2" npt. I needed 3/8" npt. Late model heads on my engine.
So I turned the 1/2" npt down and threaded for 3/8"npt.

 

[mrk5]

I've been guilty of just doing the swap without draining coolant. Just gotta be quick. Obviously coolant will be lost. Next time I'll try Wes's trick.

 

[wazzabie]

I got a new temp sensor. I wonder if there is any way to test the new sensor before I install it.

 

[Wes Harden]

boil it with a candy thermometer and ohm check it