GM does have a huge problem with leaking intake manifold gaskets. If there are no obvious leaks that you can see, the best approach is to add a small bottle of dye to the coolant, drive long enough for the level to go down in the reservoir, then search with a black light. The dark purple dye will show up as a bright yellow stain that you can follow back to the source of the leak. If the intake gaskets are leaking, you'll see the stains on top of the engine or inside the tail pipe. You may not see coolant on top of the engine if it evaporates as fast as it leaks out.
Also check at the air conditioning drain tube under the hood on the passenger side of the firewall. If the stain shows up there, the heater core is leaking. That is real common on GMs. It is aggravated by their use of Dex-Cool, ("Dex-mud") antifreeze. Acids form in it that eat away at the radiator, heater core, and other metal parts. A common complaint is finding new replacement heater cores leaking after as little as six months. A digital voltmeter can be used to identify an antifreeze problem. Any two different metals and an acid cause "galvanic action" which is what causes batteries to produce a voltage. That is a type of corrosion. This problem can be found with the voltmeter by placing one probe in the coolant and grounding the other one to the battery negative post or to the engine. The higher the voltage, the more corrosive the coolant.
Tuesday, October 11th, 2011 AT 2:24 AM