97 blazer, temp guages bounces back and forth from hot to cold. Engine is not overheating. Have replaced coolant sensor guage but did not help. Coolant level is good. Need some advice!

 

If replacing the sending unit did not help, the wiring at or near the sending unit is likely at fault. The sensor varies the resistance to ground in response to the coolant temperature. If the wiring and/or connector have intermittent connection caused a dirty/corroded contact or a broken wire inside the insulation, it could cause the symptoms you describe.

The gauge should read cold with the wire disconnected (infinite resistance). It should read hot when the wire is grounded to a good ground point (low resistance). The wire in question should be dark green and it runs from the sending unit, through the firewall, to the gauge cluster. Testing this wire with a multimeter should show relatively low resistance and the resistance should not change while flexing the various wiring harnesses/connectors/etc. If it does, replace the wire.

It is worth noting that your truck has two temperature sensors. The one for the gauge is located in the driver side cylinder head. The other, for the PCM, is located near the thermostat housing.

 

Thanks for the information. I have replaced both sensors. I have not checked the wiring yet. Will inform on progress.

Also, I have a starting problem. If I use starter fluid the truck starts great. It will sometimes start without the fluid. Replaced fuel filter, it did not help. After the truck starts it runs like a top. So I do not feel like it is the injectors or pump. I am thinking it may be the ignition module? I have had a mechanic put it on a machine and no code appeared for either problem. He suggested ignition module or distributor. Which do I replace first? And will the ignition module help with the temp guage problem?