losing antifreeze. any advice?

[taylor7212000]

i have a 99 bravada with a 4.3. i started noticing that i was losing coolant. every couple weeks i have to put about 1/2 gallon into radiator/overflow tank. im not sure if it an intake or a head gasket. so i am in the process of changing both via myself. the weird this is. my dipstick looks clear no signs of anything getting into the oil and there are no leaks anywhere. i dont even see anything on ground under truck. when it doesnt run overnight the motor sounds really rough for about 2 to 3 minutes and then sounds normal. what i think is happening is the intake is letting coolant into the cylinder and when everything warms up the gasket reseals until cool again and i am burning off what is in the cylinder. i just have never ran into either a leak from a hose or on the ground or seeing something in the oil. i just want to take sure im doing what i should be. right now i got both valve covers off and throttle body off. working on it a little later today. anyone with some advice would be great

[MT-2500]

What is the mileage?
Any signs of heating up under a heavy load when it is full of coolant?
Head gasket or intake can leak external or into the engine oil.
And head gasket coolant leakage can also go out exhaust pipe.
If leak is very bad you will have white smoke and coolant smell

They make a leak dye for the coolant that helps in finding small hard to find leaks.
A pressure test cold and warm and hot helps to.
Coolant leak into cylinders can be either intake gasket or head gasket or a small crack in the head.
For head gasket leakage they make a chemical block tester to catch head gasket leakage into the cylinder wall.
It will pick up exhaust gas in the rad.
Also pulling the spark plugs and looking at the color of tip helps find coolant getting to cylinder.
Or pulling plug and pressure test rad and crank over engine and see if any coolant blows out.
Coolant in oil is hard to see unless there is a lot of it.
First sign is oil turning red /pink.
9 out of 10 times the intake leaks and you can usually see a bad gasket when you pull intake.
If replacing intake gasket us the new hard rubber backed problem solver gaskets by fel-pro gasket co.
Also GM is picking up tabs on a lot of the intake leaks.
http://www.girardgibbs.com/news.asp

http://www.dexcoolsettlement.com/

http://blogs.cars.com/kickingtires/2...s-out-for.html

[taylor7212000]

there is nothing in the oil. and a little smoke out of exhaust when i first start it but then it goes away. i took off the intake and the gasket did have a slight break init. im in process of putting it back together. finishing tomorrow. ty for the help. i believe i solved it

[partsmgn]

i had an 88 6000 which had a blown head gasket.....it never leaked into the exhaust or into the oil....when at idle it never leaked at higher rpm it was spraying it out at an alarming rate. (i even had a pressure test done on the system and it still never found the leak)

[MT-2500]

Originally Posted by taylor7212000

there is nothing in the oil. and a little smoke out of exhaust when i first start it but then it goes away. i took off the intake and the gasket did have a slight break init. im in process of putting it back together. finishing tomorrow. ty for the help. i believe i solved it

Good luck and let us know how it goes.
MT

[99BlueBlazer]

My 99 Blazer w/ a 4.3 started doing the same thing around 100,000 miles. I expected the problem to be a bad intake gasket, but surprisingly it was not.

The water pump was worn out and had sprung a small leak. Replaced the water pump and solved the problem.