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I was loosing about a glass of water mysteriously every 100 miles so conventional wisdom on this forum had me replace the head gasket. I had the head resurfaced at the same time.

Now everything is back together, and the temp gauge is acting wacky. Initially I drove the car around the block and about halfway around the temp gauge screamed up to max. I immediately shut the engine off and coasted home. I let the engine set for awhile and the gauge stayed pegged way after the engine had cooled down. I removed the wire from the sending unit and the gauge fell to nothing. I shorted the wire to ground and the gauge maxed out. I then reconnected the wire to the sending unit and the gauge read about half way up. This is all with out starting the car and having let it sit over night.

From this I replaced the sending unit. Now the gauge starts off at nothing and then screams up to about half way all at one jump. Not slowly. Then after the car is running for awhile I hear a change in the motor idle and the gauge jumps high. If I shut the vehicle off and restart it immediately the gauge returns to about halfway.

Anyone have any ideas? I don't think the car is overheating. The fans are not coming on. What else could be causing this? Thanks kevin

 
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Are you actually losing any coolant now (burning or dropping) or is the gauge just going up on it's own? Did you make sure to torque the head bolts down to proper torque and in the correct order? You could try popping out the thermostat and testing it and replacing the thermo gasket while you're at it. Replacing the radiator cap might also be a good idea, especially if you're opened it several times to replace coolant while it was overheating. Also, did you replace any other gaskets while you did the head gasket job, or the head gasket only?

 
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the sensor for the temp gauge doesn't control anything else so I wouldn't worry about it too much. The fans are controlled by another sensor altogether. Besides if you were overheating you would have seen smoke coming out from under the hood. (coolant boiling over, engine grease burning off)

 
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I have not run the car for more than about 5 minutes so I don't think I'm loosing any coolant. The gauge is just going up and down. I didn't have an overheating problem before replacing the HG. The only symptom was I was loosing water and had no leaks and the reservoir was not loosing or adding water. Water just disappeared from the radiator.


Yes


I replaced the cap before the HG in an attempt to rule out everything before replacing the HG. The car was not over heating before replacing the HG, so I kinda doubt it would be the thermostat.

Replaced intake/exhaust manifold gaskets. Valve cover gasket. Head water outlet gasket.

I've read something about air in the system could cause this? I replaced the sending unit that has the single wire coming off that is under the dizzy, and tested the cluster gauge by shorting and un-shorting this wire.

Before I replaced the sending unit, the temp gauge screamed up to max out pegged after only driving about 2 minutes around the block. Now it doesn't peg out but it still jumps to about half way and then after I hear a change in the pitch of the motor it creeps up to about 3/4 of the way and I shut it off before it goes any higher. If I immediately turn it back on the gauge is back to less than half way.

To bled the system do I just crack the bleeder on the top of the water exit port on the head? Thanks Kevin

 
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I'd definitely try bleeding the coolant before you do anything else. It's pretty simple. Just idle the car with the heater at max and the fan off until the cooling fan kicks on. You can jack up the front of the car beforehand to help the air get out too, if you prefer. You can crack open the bleeder bolt if you don't mind making a mess on your shop/garage floor.... orrrrr you can buy one of those special little funnels that sticks into the radiator cap hole before you start idling the car. They're pretty cheap at the autoparts store, iirc. Either way, get all that air out of the cooling system before you move on troubleshooting.

 
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2 min is too fast for engine to overheat. 5 min as well.