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I have recently acquired a 30000 mi /96LT4 car. Would like to replace the coolant as am seeing signs of the Dex-cool red molasses looking junk in the overflow tank. Have read all previous posts re OAT/HOAT etc and am leaning towards G05. Can someone suggest a best practice procedure to follow in flushing system. Thanks.
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Re: Anti-freeze flush
I just recommend thorough draining (open both block drains) then a thorough water flush. This can be done cold. Remove the heater inlet hose at the inlet manifold to flush the block and heater circuit.
A hot flush can also be useful. After thorough cold flushing fill the system, start the engine and bring it to operating temperature for about five minutes.
Once the effluent is colorless and tasteless, the system should be clean.
This is also a good opportunity to replace any coolant hoses that might be suspect.
Dexcool can develop problems if the system is run below minimum level for any length of time.
Do you have proof the the Dexcool was ever changed? It should have been changed circa 2001 and would be due again in 2006. Low mileage cars often are not well maintained. Owners think: "If I don't drive it much I don't have to do any maintenance". You would be wise to flush out the brake system, too. I bet the brake fluid is original.
For a system originally equipped with Dexcool, I would stick with it - 50-60 percent Dexcool/water, and change it every five years.
Duke -
Re: Anti-freeze flush
Having a original owner 96 LT4 I have only changed the coolant once and will again next year. If you have the owners manual look on page 6-26 top left. In addition to using DEX-COOL 50/50 with water it mentions perferably distilled water. I did this. It also mentions with a complete coolant change that to use GM Engine Coolant Supplement (sealer) GM Part No. 3634621. The supplement is 6 brown tablets that are installed in the surge tank after adding coolant and distilled water to the system, so leave enough room to add the tablets and top off with fluid. In addition to draining the radiator the block will need to be drained of old coolant. Your 96 LT4 has two knock sensors screwed into the block drain holes. The knock sensors are easy to remove, your LT4 should have protective shields covering the knock shields that will have to be removed to provide access to unscrewing the knock sensors. They should be easy to remove, which means only replacing them tight enough to not leak. I used a small amount of anti-seize when I reinstalled mine. I removed the coolant recovery tank and flushed it as well. There is an air bleed valve that can be opened to bleed off air in the system when you are refilling it. I installed the measured amount of DEX-COOL first and them followed with the distilled water. I did this with the engine cold. I did not flush my system since I had no cooling system problems and was only changing the fluid. Opening both block drains and draining the radiator removes a lot of coolant. The stuff in the coolant recovery tank you mentioned could be the mixture of the factory installed engine coolant supplement sealer with the coolant. This sealer is also mentioned to be used in the 96 Corvette service manual. I did not have the "molassas" looking stuff in my recovery tank like you mentioned. Perhaps someone put the tablets in the coolant recovery tank instead of the surge tank. I overfilled my coolant recovery tank with new 50/50 mix of coolant knowing that some void in the engine with the fluid change would pull more fluid into the coolant system after driving and it did.Comment
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