Sounds simpe, right? The "Low Coolant" light on my dash turns on shortly after I start my truck (within 2 minutes) and stays on. It came on a couple of times previously in the past 6-8 months but I just added some coolant and after restarting the truck, the light would go away. But, beginning last Tueaday, it stays on, even though I added coolant and the reservoir is full to the point it should be (if not slightly higher). Not sure where the low coolant sensor is located or if that could be the problem. Engine temp seems to be fine, it never goes above 200 degrees. Obviously, having to add any fluid 3-4 times over a 6-8 month timeframe indicates the coolant is going somewhere (it's not in the engine oil). I can occasionally smell antifreeze but I have yet to identify any obvious leaks around the water pump, hoses or radiator. Any suggestions? Truck has 175K miles, original water pump, radiator, hoses, thermostat, etc. Original coolant too, except for the add-in over the past 6-8 months which has totalled about 2 gallons.

What year?

2002

Assuming its a V8, look closely around the water pump for white crusty streaks. It might be evaporating before it can drip anywhere. Usually the Castech head problem would have shown up already. If its a V6 it could be lower intake manifold gasket.

It's a V-8, the small one, 4.8 Liter. I'll take a look around the water pump to see if there is any of the white crusty streaks from the antifreeze. What is the Castech head probkem?

Castech Head TSB

http://ww2.justanswer.com/uploads/Bluegorilla/2008-12-05_142924_Coolant_loss_5.3.pdf

if it is full, and the light is still on.. there is buildup on the sensor. I tap the jug a few times with my hand to knock it off and it seems to work for awhile.

i experienced the same scenario as you with smelling the coolant, but not seeing a leak. turned out my waterpump was going out.

I'm praying it's the water pump and not cracked heads. At 176K miles I would expect the water pump to be reaching it's full life (and probably more). Guess I need to give Brian (liteliner) a call and have him come check it out. Thx guys

VERY GOOD GUESS

I have a 2003 Silvarado Duramax that had a similar issue. Before looking at big fixes, try a new pressure cap on your tank. It fixed mine. I eventually had to replace the water pump but it was over a year later. Might give it a try.

Had a very similar problem with my truck 2005 GMC Sierra with the 5.3 as far as the leak. I put a bottle of this http://www.barsproducts.com/C16_R6.htm in it and it sealed whatever it was.