I have noticed in my '91 Nissan Pathfinder's its engine temperature guage never goes above a quarter way up. I see that other people have posted this, so I assume its normal, but mine is coupled with something else. My heat take about 15 minutes to start even blowing slightly warm air, and it never gets hot. It always is sorta warm-ish. Is this normal with Pathfinders? I mean I love my truck to death but living in NH, winters can be brutal with sucky heat. Could this have to do with my thermostat...? If so how hard is it/how much is it to replace it? Thanks.

See if the fan clutch is stuck. It would be always cooling even when it is cold. See?

If you can not turn the fan with the engine off, you need a new fan clutch assembly.

It could also be the thermostat is stuck open. Does the upper radiator hose get warm immediately? can you feel warm water in the upper hose immediatey? The thermostat is attached to the upper hose.

The stuff behind the nissan grille guard (http://www.shopnisparts.com/nissan-grille-guard/) already needs to be changed.It could be the fan clutch that is malfunctuning or the thermostat.

I do not understand what you mean when you say, The stuff behind the nissan grille guard already needs to be changed.

Is there any chance that redmansioner is a robot? his posts are worded strangely, have links to commercial sites, and I can not search for "find posts by red mansioner."

Redmansioner, what do you say?