Temperature gauge keeps fluctuating up and down close to red?

This problem is noticed on many car models.In this case the problem is noticed on 1997 Mazda 626.
First of all,turn the engine off and see if you notice any coolant leak.If yes, then that is the cause of problem.The coolant level is getting low and causing the temp gauge to fluctuate low to high in red zone.


But if there is no coolant leak,then other possibility can be faulty thermostat.
That could be the thermostat, you may want to take it out and check it in hot water to see if it opens, however,

With any engine that has been run hot, over heats or has been run hot, the first thing to is check the integrity of the internal engine, (ie. Head gasket(s) and head(s) and block) . Then consider the radiator being restricted somewhat.

You can check for cool spots in the radiator’s core that would indicate a clog.
The first thing that you want to do is check the cooling system for any exhaust gases. There is a tester for that, that you can get from Autozone service center for about $20. It comes with instructions, but there is a blue fluid that is used in it, if the fluid turns yellow, that is exhaust gases.

Block tester available as:
OEM/Block Tester AUTO ZONE

Part Number:
27145

If there are any exhaust gases in the cooling system, that will cause more pressure than desired and will allow the engine to burn coolant and/or heat the coolant up too high. Most times not filling the crankcase with coolant either.

If there are, then there would be an internal engine problem, like a head gasket or head.

Of course, you will want to make sure that the system is full, the coolant is circulating, and the cooling fan(s) are working as well as the pressure cap holding pressure.

This details will help.

Thanks.

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