Although I do not see any signs of overheating and the thermostat gauge looks good, I have had the Low Coolant light come up 2 times in 3 days. After I shut off the engine and when I go to check it, it is really low in the reservoir. As the engine starts to cool, the reservoir starts to fill up. It fills up faster if I slowly open the cap to let a little air in. It's as if, the vacuum is pulling it all in. It will fill back up almost to the full line in the reservoir tank. A little history, I have recently replaced the thermostat and most recently replaced the water pump (approx a month ago). There are no signs of leaking of coolant that I can see but I do smell it coming from the engine compartment when I get out of the truck. If there is a small leak, it must be occurring while driving. Any thoughts or suggestions, would greatly appreciate it.

 

does the vehicle use a surge tank ...ie surge tank is pressurized...coolant reservoir is not pressurized.

 

Yes, it has a reservoir. Every time I take off the cap, it acts pressurized. When I take off the cap, the tank starts to fill back up.

 

I need to know what type of system it uses?? post a pic of the surge tank/reservoir. Include engine size
99 old body style uses a different design than a 99 new body style.

 

search past threads in this forum: i'm unsure if this applies to 1999 or just 2001

YOU MIGHT HAVE THE FAMOUS PLASTIC HEAD GASKET PROBLEM

mexico put in plastic head gaskets (abhorible!) , then GM used used canadian recycled fluid which ate plastic (also a seedy practice). the result is: holes in plastic allow coolant to be eaten in the combustion chamber by leaking through holes in plastic - and you think your coolant keeps "going low"

the answer is: GM has replacment aluminum/plastic gaskets and says not to used the ?DEK coolant (use only non-recycled Prestone made in usa fluid with the new head gasket !)

note: i assume it's going very low (under minimum ilne) not just "being lost after topping off". if you fill to top cold, and drive until hot: then it's supposed to spill out until slightly lower than "full hot" that's it's design

 

Canadian recycled fluid...new to me.lol Where did you get that?