1990 buick century thermostae removal trouble

Have to remove the least amount of things that
is necessary to get at the thermostat

That is a pretty common problem even back in1990
& today forget it

The fuel pump for a 1990 Buick Century is located inside the fuel tank.

75 series

I would guess it is metric,as are most all bolts,except some large size chassis bolts,and have been since about 1983. You got rust issues also.

Change thermostate and make sure there is enough coolant (not water) in the system.
Check that the thermostate sensor is working properly.

Disconnect the battery. If light comes back take to shop to read Diagnostic Trouble Codes.

Remove any add on pulley extensions, remove center bolt (generally very tight) and use a harmonic balancer puller (that is a specific tool) to get it off.

You will need a good pair of 45 degree long neck needle nose pliers to remove the clips for the motor arms, and yes it can be a bit trying of ones patience and mechanical skill level.

Hello, the crank position sensor or (CPS) censor is located directly behind the harmonic balancer (or fly wheel at the very bottom). The sensor is located on the right side of the harmonic balancer when facing the front of the motor. You must remove the harmonic balancer to replace the sensor. You must also re-align the sensor with 30 thousands of an inch tolorence, or your car may idle rough or may not start. I own a 1990 Buick Century and just replaced my CPS sensor last month. There is a trick I learned to reinstalling the new sensor. Let me know if you need that information.

Here's a freebie: go to 'autozone.com enter your car info (year, make, model, engine) click on repair manual, then chassis electrical, then to the far right of screen and down, wiring diagrams. Let me know if u have an trouble locating it.