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2004 Chevrolet Silverado 1500 Base Reg Cab 119.0 WB Work Truck

2004 Chevrolet Silverado 1500
Trim Info:
Rear Wheel Drive, Reg Cab 6.5' Fleetside
15 mpg city / 21 mpg hwy
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May 7, 2013, 5:01 pm

John S

Question: 2004 Silverado Antifreeze leak

I have had an antifreeze leak on my 2004 silverado with a 5.3. When I start the vehicle the A/F tank empties and slowly rises back up as it comes to an idle. If I hit the accelerator agian it empties and does the same thing. It has a small puddle that builds up under the front passenger side when I park it. Oil seems fine, no sign of antifreeze. Slowly go through a gallon every 1-2 months, driving 70 miles a day. Checked the radiator and there is no sign of a bad gasket. Any suggestions?

May 24, 2013, 1:35 pm

Elizabeth K

First, it's important to understand the relationship between the max/min or hi/lo marks on the overflow tank and the temperature of your engine. If the engine is cold, the MIN line means 'full'. If it's hot, the MAX line means 'full'. It's easy to think you have a coolant leak if you are filling it to the MAX line with a cold engine, as the excess will boil over and the next time you check it cold, it will be at the MIN line.

Once that common misunderstanding is out of the way, is the puddle under the engine compartment anti-freeze, or is it water? Is it directly underneath the overflow tank? Is it underneath the firewall? When you say it slowly builds up, is that overnight or over weeks?
Does the puddle increase in size when you use the a/c more? If so, and it's water (not antifreeze) then it may be from a plugged up a/c vent.

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May 28, 2013, 5:05 am

John S

Still doesn't explain why I am going through a gallon of antifreeze every 1-2 months. There has been no issue with the A/C, problem seems more of an issue during the winter months while using heat. Is there any possibility that the thermostat could be sticking causing backpressure and leaking out of a hose. Also noticed while I was pulling a 2-3 ton load this weekend I hit the accelerator to pass a vehicle and had a strong smell of antifreeze. I do get a slight smell once in awhile of antifreeze, but not daily.

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May 28, 2013, 5:16 pm

Elizabeth K

Is the engine overheating? If not, do not worry about the thermostat. If you think there is an external leak but can't find it, have it pressure tested at a shop--they can pressurize the cooling system and find pinhole leaks. Are you having white smoke out the tailpipe after the engine is warmed up? If so, you probably have a blown head gasket.

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May 29, 2013, 4:05 am

John S

I check the tail pipe from time to time for white smoke/vapor since I started noticing the problem. I guess my best bet is to have the system pressurized.

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May 29, 2013, 5:58 am

Elizabeth K

One way to test for a blown head gasket is to look at the overflow tank while revving the engine. If exhaust gasses are leaking into the cooling system, they will show up as a stream of bubbles rising up from the bottom of the overflow tank under load. Your description of the overflow tank emptying is not what I would expect, but it is a reason for further inspection. And if you are smelling antifreeze when accelerating, that does show a correlation between radiator pressure and engine load--which should not be happening unless there is a breach of the two systems.

Based on those 2 symptoms, i am surprised you're not seeing a giant plume of white smoke when you drive down the road. A compression leak-down test would be helpful--the cylinders are pressurized, and then you listen for an air leak--you can tell what's going on by listening for the air escaping through the radiator, exhaust, etc.

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