Coolant loss

RUDY0287

MEMBER
2001 CHEVROLET SILVERADO
4.8L
V8
2WD
AUTOMATIC
145,000 MILES

Loosing quite a bit of coolant with no visible leaks. I did pressure test four times, twice cold and twice hot at 15 lbs. No pressure loss, no visible leaks. Each test was for thirty minutes. Then did four block test using a block tester with liquid chemical. Two with engine cold and idling and two with engine hot and idling. Again all tests were negative. Each time I checked against the exhaust at the tailpipe and it was always positive. The liquid turned yellow. What I did see was fluid coming out of the tailpipe. I changed the oil and saw no indications of fluid in the old oil. Not really sure what to look for but the old oil looked normal. No milky residue on oil filler cap. Any help would be greatly appreciated.

Wednesday, January 30th, 2019 AT 11:52 PM

5 Replies

PATENTED_REPAIR_PRO

MECHANIC
1,853 POSTS

It sounds to me as though you have coolant leaking into the combustion chamber.
If this problem had just started it probably hasn't had enough time to accumulate white milky residue under the oil fill cap. You most likely have a head gasket that isn't completely blown but leaking enough, or possibly even a crack in a cylinder wall. I would remove all the spark plugs and look for any coolant on any plugs that way you can pinpoint which cylinder it is, know at least which bank it is, etc.

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Thursday, January 31st, 2019 AT 3:10 AM

RUDY0287

MEMBER
8 POSTS

Thanks for answering. The problem has been going on for quite some time but has gotten worse in the past few months. I know I have a problem with sludge, I did remove the valve covers and it was really bad. Cleaned up both heads and flushed engine, cleaned oil pan and pickup screen and just about anything I could clean. Have changed the oil twice at 1,500 mile intervals since the clean up and plan to do one more. I also replaced the intake gasket. Truck runs really good and does not overheat and never has. If I have a bad head gasket or head why would I get negative results with the block test? One more thing, I have noticed an increase in oil pressure. It has run at approximately 28 to 30 lbs at idle for years and now at about 40 lbs at idle and will go to 60 to 65 lbs on freeway doing 70. I guess a tear down is in order? Any other information you can give me would be great. Thanks for the response.

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Thursday, January 31st, 2019 AT 3:52 PM

PATENTED_REPAIR_PRO

MECHANIC
1,853 POSTS

Tests do give false positives sometimes, I was just going by what you said here, " I did see was fluid coming out of the tailpipe". If you really want to clean the sludge out of everything try adding a pint of Gunk engine flush, to a cold engine let it idle for ten minutes, drain the oil and filter and then check and see if the oil pressure comes back down after topping back off with new oil and make sure you at least drain the filter to of the cleaner.
If you decide to tear it down send out the heads and block to be acid dipped, normally done at a engine rebuilt shop.

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Friday, February 1st, 2019 AT 3:11 AM

RUDY0287