My engine light is on, and my car is overheating,how can i check if the problem is the thermostat ?

you have overheated the engine maybe thermostat or water pump fault

I"m not sure what the problem is, this sounds like the engine light is coming on because its overheating and you replaced the airpump and alternator and now you thinks it is the thermostat. if this is correct then yes replace the thermostat and also check the fan clutch, when engine is hot the fan should not spin freely. and last are you sure the engine light is on due to it overheating, if it is due to overheating then check fan clutch and replace the thermostant

Check fan belt tension and/or coolant thermostat. When the engine is cold, no coolant flows through the engine. Once the engine reaches its operating temperature (generally about 180-200 degrees), the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.

code po 1258 is an overheating code, need to check why u r overheating, start simple, do u have fluid, has it been changed , might need thermostat, how old is truck,. is there a leak anywhere.do pressure check on radiator and see if it leaks, check radiator temperature vs engine temperature. get a thermo scanner they work good. point and it reads how hot . if motor is hotter replace thermostat. check make sure oil level is good. get back to me let me know what u find..

no it might have problem inside the engine also the check light should lighted get it diagnose to find what is the problem overheating really problem on the engine might be also thermostat issue have it check specially with check lights are on

About the only things are the thermostat and the water pump.There could be something with the radiator but that is the rarest because the water shoots straight through.If it overheats fairly rapid,it's most likely the thermostat.Sometimes a water pump will let you go 20-30 miles before overheat.The thermostat is cheaper and easier if you're going to try it systematically.Overheat will probably cause the check engine light too.Good luck! Greg

You didn't say what year your car is. Change your thermostat it is in the housing at the end of the top rad. hose. as far as check engine lite goes go to auto zone they will check your codes (FOR FREE) do not drive hot WILL BLOW HEAD GASKETS also if car is 10 years or older check your rad. hope this helps CJ PSchange thermostat first

If engine is overheating then check coolant level and thermostat first, then water pump. If engine is not overheating then check coolant temp sender for gauge.

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Could be three things: Hopefully the first...
1. radiator fan not blowing. (most likely)
2. Radiator clogged (not likely)
3. Head gasket blown... (very possible)

If #1, system cannot detect fan not blowing. It may be the fuse or the relay switch, disconnecetd wire at fan, or burned-out fan motor.
If #2, Flush radiator
If #3, you will see WHITE smoke out the tailpipe and excessive water drops.
Your new oil will have a "milky" look (check the oil dipstick). That is water.
When engine is COLD, remove radiator cap and start car. You will notice high-pressure "bubbles" squirt out of the radiator, even before the engine warms up.

I hope it is #1. and that this is helpful.

there is a coolant cap on the overflow bottle check it for seal
i'd just replace it
also if you put the new thermostat in backward the overheating would be significant