When adding coolant, best method, get a funnel and put it directly into the radiator (it will help reduce how much air you have in the system and hopefully ensure you have the right amount of coolant in the system). Going into the overflow bottle, you won't have as much as you should (and you'll have a LOT of air in the system).

And it's clear in those pics it's NOT a water pump leak (as the pump is on the other side).

Unfortunately, the pics don't show the source. You will need to borrow a radiator pressure tester from the auto parts store. This way you can safely increase the pressure to about 13lbs on a cold car and look for leaks.

Roughly based on the location of that leak, it is one of the following (and it should be where you focus your leak check):
- Throttle body gasket (as coolant passes between the UIM and the underside of the throttle body).
- Failed UIM gasket. It has 2 ports for coolant travel (the path goes from the LIM, to the UIM, to the throttle body, back down the UIM, back into the LIM). These have been known to fail.
- Failed UIM (less likely, as typically the coolant leaks into the air intake, not out of the engine when this happens).

If any of those leak points is confirmed your failure, to DIY, the HIGHEST cost is about $100 + anti-feeze. The most expensive fix it the UIM. But if you have to replace it, the Bonneville guys highly recommend the APN UIM (it no longer says APN, but the link below is to it):
GM Intake Manifold Kit
A couple Bonneville guys helped build this kit and make recommendations to improve the UIM. I did not see a throttle body gasket it in the pic on that site or description, so if it's NOT included, that it like a $5 gasket.

I have not used the UIM, so I can't confirm, but I've heard if you intend to use a ZZP HV3 UIM insert mod, that it will not direct fit into this UIM (I cannot confirm this information, it's hear-say nor do I have a thread that confirms it).

 

thanks maniac very informative. i have a heard time getting the radiator cap of tho, i twist and pull and still wont come off, how u get that sucker off?

 

GM used a metal radiator cap on some cars and a plastic one on others. Not sure if all the '00+ Montes had a plastic cap (I know mine does). It takes a lot of twists to unthread it from the radiator. Then if it's completely unthreaded, it has a big/thick O-ring on the cap. If that cap has not been off in a LONG time, ods are the O-ring is "sticking". It just takes a LOT of pulling (and wiggling with an upward force) at that point.

And if it is sticking, even though anti-freeze should work as a "lubricant" it may be a good idea to hit the O-ring on the cap with a lubricant (just to avoid it sticking in the future).

 

neither of mine leaked, either. good luck.