3TB Drive Formatting from 801GB to 3TB

This is more of a solution rather than a problem i purchased a 3TB (Seagate Drive) as my iMac said there was a problem with the temp sensor on the drive and my computer kept crashing so a want to fit a new drive but turned out that disk utility only saw 801.5GB of the drive. any after reading these forums they were of little help.

So what i did was select view all from disk utility select the drive the top level one beginning with S and lots of digits,

select erase then select format APFS only once done this will show the drive as 3TB, then select the untitled drive and erase that drive this time format it as Mac OS (Extended) Journaled.

You can now use the drive as its intended capacity. I used super duper to make a full image of my failing drive.

But the real problem was the iMac power supply tripping out on thermal sensors