Coolant leak 2003 sierra 2500 crew cab, gas engine. Great truck!

Check engine coolant level. Make sure no coolant in engine oil (crankcase).

Add coolant if low. Check immediately and a few minutes later... if coolant low again identify leak or check oil level. Dont run engine if coolant in oil.

CHECK ENGINE OIL FOR SIGNS OF COOLANT,IF ENGINE OIL LOOK OKAY MORE LIKELY WATER PUMP COULD BE LEAKING.CHECK AROUND WATER PUMP SEE IF WET WITH COOLANT.

Check your transmission dip stick to make sure it's not going in to your transmission from a bad transmission cooler which is incorporated with the radiator.
The only other thing that i can think of, which is common is the intake gasket may have failed and your losing your coolant from there and being burnt through your engine. If it's a slow enough leak, your not going to see any coolant cause it's going through your engine's combustion chamber with the intake air.
Thank you for using fixya and good luck.

i have a 04 sierra 2500 hd, i put a spectre cold air intake and it boosted my economy to 11 city 16 hway and it was only 150 at autozone

check under the hood in the wiper cowl, should be an access panel. if not check behind the glove box.

Possibly a blown headgasket or intake manifold gasket. You would have to start a teardown to find it

Recheck your work may have something backwards put selector in ac and see if you have heat may have the cable backwards

AUTO DASH SAYS 'REDUCED ENGINE POWER" TRANSMISSION FLUID SEEMS OK AND COOLANT OK. WHAT ELSE COULD IT BE?

actually it is not good idea to replace your coolant by water only you shoul full your coolant system 50/50 mixture coolant and water because coolant has uniqe smell and color so easier to identified leaks.
first check your oil condition and coolant reservior for any coolont oil mixture for figure out head gaskets condition if you have any oil coolant mixture in oil or coolant you have a blown head gaskets this will send you to mechanic if everthing looks clear then go front driver side bottom of radiator and open the drain **** (make sure car is cool and put container under because coolant is toxic and mess up your drive way )open reservior tab too and drain all the water close back drain **** probably your vehicle prefer dexcool(red color)
fill 3 qt dexcool then water or just buy ready mix run the engine with reservior tab open and check coolont level add more if necesery suquize collont hoses for air inside when engine start hit up close reservior tab. on passanger side front of the engine has a coolant drain plug open with number 8 wrench untill you see the coolant come out( bleed the system for air) make this several times turn on your heat too and bleed again and watch your upper and lover hoses for any visible leaks fallow small coolant lines like under throttle body check thermostat housing under throttle body on 3.4l engines check under radiator if your pressure cab dosen't look good get a new pressure cab .shut of the car and check for leaks once you find out where is leak from easy to fix it.

Is this a small amount of white smoke or a lot of white smoke? If it is a lot of white smoke it could be a head gasket problem.

1. Do you have coolant in oil or vice versa?
2. Pull spark plugs and inspect for plugs wet with coolant.
3. Do a compression test and check for a low cylinder.

If you have issues in any of these points you will need to replace the head gaskets.