overheating problems

[kamash]

I have a 87 caprice it just started overheating yesterday, also when I took it for an oil change they mentioned that my oil was kinda mixing with water, even though another mechanic said it was not and all I needed to do is change was my lifters (tappets).
that has been a while and then all over sudden the car starts to heat up, I wanna change the thermostat for a start then go from there.
My only dilema is where do I find the thermostat! is it easily accesible. with my ride overheating I am losing too much power and my oil pressure light is coming on but I do have enough oil!! If anyone has any ideas please help Thanks in advance

[MRTeeShot]

if the oil press. is dropping it is prob what is causin the over heat if you cant do it yourself take it to a mechanic and have him give it a look if your oil pump is goin out it will destroy your engine so do it soon and dont take any long rides or it may go boom

[TommySS]

The thermostat is inside the housing where the top radiator hose connects.

Water in oil could be a leaky intake, blown head gasket, or other stuff.

Check the oil. If it is kinda milky, you have water in it.