temperature going up and down.

I just installed a radiator from an automatic, before that I had an ef radiator and it use to warm up just fine.
But then when I got the automatic da radiator it would never fully warm up. People tell me it’s my thermostat.
What could it be?
Plus I know the thermostat is mechanical so if it was to not work it wouldn’t work.

i dont know what youre asking. are you saying that you no longer reach “normal” operating temp? where does the needle on the temp gauge sit while youre driving?

the thermostat could be stuck open if the car stays cold. its easy to troubleshoot. take it out and look at it or put it in a pot of boiling water and watch it do stuff…

The needle goes up and down. Some times it warms up all the way where it needs to be.
its usually like 1/4 up or less when I’m driving.

well the average spot is just before the little picture of the thermometer which i would say is about 1/4 of the way. can you post a picture?

Ill put one when I get the chance, but yes its suppose to be before the thermostat on the gauge which would be almost 1/2
But mine is at 1/4 and then it goes back down.

I could be mistaken, but for some reason I remember having an issue like this and there is a single wire sensor directly under the distributor that can come loose or part way off and cause the gauge to move up and down randomly…kinda sounds like what you may be dealing with, maybe not, but worth checking none the less and takes all of 5 seconds.

I swear that happened to me, but I may be thinking of somethign else entirely. I dunno.

it’s either an inaccurate reading,or the tstat is sticking. as mentioned, check the sender wire connection. it is a single wire under the distributor. because of the location, it sometimes gets covered in oil and reads inaccuratey. because the sender is a negative temperature coefficient sensor, the higher the resistance, the colder it will read. so a poor connection or poor wiring would read colder. if the reading is accurate, the only part that could be at fault is the thermostat, as it controls minimum temperature. unless the fan were staying on