I want to put visual marks on my guages that indicate when a problem might be encountered. So, my question is:

1) What PSI would be considered low engine oil pressure (where I'd want to start trouble shooting it).

2) What should be considered to be a high oil temperature?

3) What is a low brake pressure (mine is usually at 120PSI, but I don't know when I should start to be concerned about it)

4) What should be consider a high water temp. Mine usually runs around 195°, but I don't know when I should start to be concerned.

I'm going to put a little red mark on each gauge to indicate when I should start being concerned that way I'll be able to do a quick glance to see if anyting is messed up.