Temp/coolant/water pump

[Wulfaz]

1970 with a 350. Just got it for free. I realized the temp gauge is pegged on cold. Also there was no coolant. Figured it air cooled itself when I drove it home last night. (It was a cold night). Should I replace temp sensor? Or whats the most common issue with a temp gauge pegged on cold? Also how do I tell if the water pump works? On a side note I also realized the belt bypasses the ac compressor. Any advice for my first repair on this truck?

[LongBox]

Congrats on getting one of these great trucks, at a GREAT price ;-)

Obviously you want to figure out why there was no coolant. Time to yank the plugs, and do a compression check. That will help you diagnose whether there's a head gasket problem. Check the engine oil, to see if it is a milky foamy mess, indicating coolant getting into the oil system/crankcase.

If it passes these tests, I'd make sure the engine had enough good oil in the pan, fill it with water (make sure the temp is above freezing), then run the engine and look for leaks. Water pump? Hoses? heater core? rad? etc.

After this, you will have a better idea of what to do next.

[B. W.]

Welcome to the forum, great info / help here. The coolant temp sender will not read if there is no coolant in the engine. The gauge will stay on cold.

[garyd1961]

Fill the coolant first. Check for leaks next. Unless someone has added an overflow bottle it will run a little low which is just fine.

[HO455]

The guage will read pegged low any time there is no continuity to ground. So if the wire to the sender is disconnected anywhere between the coil inside the guage and the sender it pegs low. It the sender is open inside it will peg low. Easy to check the sender with a multimeter (or a test light) before removing it. Multimeter on ohms, use a lower scale, disconnect the wire to the sender, put one lead on the sender threads one on where the wire was connected. You should read continuity. Test light, disconnect wire on sender, hook clip to where the wire was and touch the other end to the positive battery post if the light glows the sender will work. Accuracy is another issue.
Before pulling things apart I would add water to see if it runs out anywhere. It could be as simple as a hose. I have had lots of bad water pumps and heater cores but very few bad head gaskets.
Good luck and congrats on a score.