99 Silverado Anti Freeze Leak

gccoley · February 18, 2008

Hey all, I have 99 silverado 5.3 and I have a small anti freeze leak. Just turned over 100,000 mile and it only leaks when it sits for a few days with out running it. Looks like its coming down the front of the motor somewhere because the anti freeze will run down the front of the oil pan and sometimes down the side of the oil pan and drip off the oil pan bolts. No enough to leak onto the ground but enough to wet the sides of the oil pan. I can't see any leak from around the intake but I haven't pulled the skid plate. Could this possibly be coming from the water pump gasket and if so , should I be able to see it if I pull the skid plate. thanks

gmtech4 · February 18, 2008

water pump

Impalacat · February 18, 2008

Sounds like the pump gaskets, that happened to me or like, gmtech4 says the pump. either way you have to pull the pump, if it's the gasket it will get worse pretty fast,I just put a new GM pump on when I pulled it apart.

'94 9c1 novice · February 18, 2008

Just did mine. 3 hours tops. Use RTV sealant on both sides of the gasket and torque the mounting bolts to specs. I let the RTV cure for 24 hours before flushing and refilling. Scraping the old gasket and cleaning the old surface is what takes the longest. I would drain the engine block if you can get to the plugs. Makes it easier and you don't have to use a rag to sop out the old coolant so the contact surace won't be wet when the new gaskets go on. I replaced the thermostat and water pump anyway because they looked original and I've got 150k on my truck. Check the hoses while you are at it. Good luck!

gccoley · February 18, 2008

Thanks to everyone for your replies, I was hoping that was all it was and not the intake. Planning on trading it it in the fall on a new HD and didn't wan't to spend alot of money on it. I have been very lucky with this truck.Never had anything done but shifter cable replaced and a few warranty things done to it . I have been real pleased with its performance as i knew the 99 models had alot of problems. Thanks again to everyone I will replace the pump while i have it off to fix the gasket.