First off, I have a 97 4runner V6 AT. It's have 145K miles.

Periodically I check the coolant and I find myself have to top it off about every 2 week. Not much, may be a quart or less each time. Is it normal? the reservoir is always almost empty. The truck have never go above half way on the temp gauge. It smokes a little bit in the cold morning, but that's it. Run fine other wise. What could cause the truck to loose coolant? Thanks in advance.

 

I have the same year. I had been loosing coolant for about 6 months or so, had a 90000 mile service and the dealership didn't catch it, but the water pump had a very slow leak. I noticed it when I went to change the upper Idler Pulley. I guess that explained the anti-freeze smell I had every now and then.
Anyway, that was my problem. Worth a check. Just pull off the timing belt cover and look at the water pump assembly. If its the water pump, should see some crusting/corrosion build-up around it.

 

If you're lucky it's something relatively simple like a weeping water pump as 97T4RNR mentioned. I also assume you don't see any other external leaks on hoses, the engine block, etc and that there is no coolant finding it's way into the crankcase (ie the oil is still transparent). It could also be a small coolant HG leak into the cylinder itself, but usually you can pull the plugs and compare to find the offending cylinder (most plugs will be a nice brown color but if coolant has been in there, they should be very clean by comparison).

 

Well, I hope it's just the water pump then. I'll check it up once the weather get warmer. Thanks