temp gauge fluctuates
 

My 2000 Solara had a failed relay and the cooling fans stopped turning. Radiator burst. Replaced all including new radiator and switches and with new relay fans are working great but the temp gauge always indicates too hot when going up an incline, even at night in moderate temperatures.....Mechanic said engine full of orange- tinted crud which is true. He flushed out radiator and rid the car of the crud but the temp gauge still bounces around....Ideas?

Did the mechanic replace the thermostat and check for a blown head gasket?

Thermostat replaced and motor very strong...It will get you where you want to go but the bouncing temp needle is nerve wracking...it runs flawlessly except for the gauge.

Is the gauge indicating too high of temp or is the engine really hot?

Is there air in the coolant system? Check the over flow coolant tank to determine if more coolant is required.

Is the wiring to the temperature sensor and sensor OK?

No air in the coolant system. Wiring seems fine. Coolant resevoir topped up....I don't think engine is hot at all....I will try a new temp guage sender and see what happens. I replaced the old sender with a new one and it indicated very hot straight away so i put the old sending unit back in.

Do this test.

Obtain a thermometer that can read up to at least 212F. Engine cold, remove radiator cap. Start engine and let warm up.

The radiator fans start up around 199F. At this temp, the temp gauge needle should be slightly below mid point and stay there.

That's a good one! I will....He says possibly slight leak in head gasket but i see no signs of such....Coolant not disappearing......No leaks on garage floor.
He also wants 1500.00 to do such a job.

The is a test called a "block test" which will sniff the coolant fumes for signs of exhaust gasses caused by a head gasket leak.

I saw one online..that's next if my switch out of the old sending unit to a new one shows no improvement. I see no leaks, the exhaust is clean and checking under the oil cap shows no white....I drove it today for 25 minutes and almost no sign of temp gauge movement until I pulled into a gas station.....When you slow the car that's generally when the needle moves upward ......Slow driving and ascending an incline......are not good. I think the new sending unit will be here Friday.

I replaced the old sending unit with a new one yet again. What happens is the dashboard gauge goes to warm as soon as the Solara starts and within two minutes the temp indicates red hot....This is identical to what happened with the other new unit I installed
I have an electric kiln which mimics this: If the heat sensor (pyrometer) has moved and the pyrometer is not one and one-half inches into the body f the kiln the kiln misfires...
These generic senders do not seat like the original sender. They will not thread all the way down into the slot. The original seats way down where it should...I need OEM!