Sbc 4.3 v6 head gasket leak? - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

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Old 09-05-2019, 12:28 PM
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Sbc 4.3 v6 head gasket leak?


I check heads and did head gasket job and other seals about 15k ago. Car was first doing bubbles after shut off and just before i remove heads there was bubbling in radiator when cap was off.

Now in last month ive noticed that there is coolant loss in reservoir. I did marks on reservoir coolant level and it has dropped two times about inch. I have hot and cold marks.

I did coolant system pressure test today. System holded pressure 10minutes, then i released pressure. No leaks and no coolant smell.

Exhaust smoke is colorless, no white. Oil is good.

I started engine without cap when it was allmost cold. Near thermostat opening there was couple time bubbles. Bubble was big and lazy, about 1/4 size of radiator neck. So couple that size bubble in two minute. After that coolant was overflowing outside radiator (because engine was warm enough) so i had to close cap.

Is there again problem in head/head gasket? Car is on daily use and winter is coming, so i must do job soon if there is problem.

Is there anything else tests to do? I must check spark plug color, how about pressurising system and spark plugs off?

Engine runs very well and temp is steady.

Help me!

Engine is 1992 chevrolet 4.3 v6 tbi.

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Old 09-05-2019, 01:41 PM
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Check the reservoir for a crack that leaks coolant.

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Old 09-05-2019, 02:00 PM
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No cranks seen and reservoir is dry. That amount of fluid usually leaves moist
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Old 09-06-2019, 06:06 AM
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Check the hose going from radiator to overflow and the neck of the radiator that connects to the overflow hose.

You can check the neck and hose by plugging the end that goes into the overflow with a bolt then pressurize the system.

The bubbles your describing is usually bad lower fins or a lower hose allowing air in. Things expand when they get hot. These include hoses.

Also do not dismiss the cap. I have solved several mystery coolant leaks(northstars that they think is instantly a bad head gasket) with a new cap and few hoses.

Caps are a maintenance item. They can allow coolant to leak past that paper thin gasket overtime.

You may not see coolant on the ground as it will evaporate especially with radiatiors that have metal sides. Now there may be some stains. But if you dont wipe down or degrease the sides these can easily be overlooked.

I would replace the overflow hose, clamps, and cap. Preventive maintance, cheap, and may fix your issue.
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