Should I flush my old Mark IV or just replace coolant? - Chevelle Tech
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post #1 of 7 (permalink) Old Feb 24th, 19, 11:04 AM Thread Starter
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Should I flush my old Mark IV or just replace coolant?

I got my car in 04, I am thinking the engine was rebuildt sometime in the early 80's. No idea of milage; but I have put on about 20K since 04. I put a new heater core in a few years ago with new hoses, replace the water pump, and had radiator recored. Engine does not run hot except on 95+ days. I have never flushed engine; however I had the engine out of the car about 10 yrs ago, so all the coolant was removed at that time. Since then I just added coolant due to repair on radiator and water pump replacement.

I am thinking I should only have to remove all the coolant and replace. Or do you think I should buy a flush kit and flush the block? I can't seem to find a video on either replacement or flush on a old chevelle BBc Could anyone outline the process of either or point me to a few video's. Heater works fine. Thanks


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post #2 of 7 (permalink) Old Feb 24th, 19, 11:06 PM
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Re: Should I flush my old Mark IV or just replace coolant?

How hot does the engine run on those 95+days, have you checked the engine temp with one of those infrared temp sensors??

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post #3 of 7 (permalink) Old Feb 25th, 19, 12:07 AM
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Re: Should I flush my old Mark IV or just replace coolant?

You should replace green coolant every 2 years, you're well past the use by date. You can probably get away with draining what you can then refill with the same color coolant. If it makes you feel better, those prestone flush kits are pretty good. Instructions in package. Drain and catch you coolant then fun the flush with good water. Drain again and if you have drains on your block drain that too. If they don't come out easy, avoid this step. You don't need to open that can of worms. Then fill with distilled water, run it and drain then refill with coolant and distilled water.

You can also drain, fill with water, open a drain and leave the car running with a hose in the radiator to get a clean change over. Open and run the heater to get a flush there too. Again, recommend the distilled water flush and coolant and distilled water for refill to avoid calcium build up.

If you don't have cooling issues, I would avoid using a flush agent or cleaner.
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post #4 of 7 (permalink) Old Feb 25th, 19, 10:54 AM Thread Starter
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Re: Should I flush my old Mark IV or just replace coolant?

Removing the block drain plugs is kind of my major concern. I think I will avoid that. Plan is to drain coolant, fill with water and run the car, drain again, fill and run car, drain again, fill and run car and drain, then add 10 qts if coolant. Then check the freeze level. My concern now is after my first drain do I always use distilled water when filling or would tap water be OK.


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post #5 of 7 (permalink) Old Feb 25th, 19, 11:33 AM
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Re: Should I flush my old Mark IV or just replace coolant?

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Originally Posted by Jim_66SS View Post
Removing the block drain plugs is kind of my major concern. I think I will avoid that. Plan is to drain coolant, fill with water and run the car, drain again, fill and run car, drain again, fill and run car and drain, then add 10 qts if coolant. Then check the freeze level. My concern now is after my first drain do I always use distilled water when filling or would tap water be OK.
I would always use distilled water. You might need more coolant than a 50/50 mix at first because of the water already in the engine.
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post #6 of 7 (permalink) Old Feb 25th, 19, 7:02 PM
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Re: Should I flush my old Mark IV or just replace coolant?

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I would always use distilled water. You might need more coolant than a 50/50 mix at first because of the water already in the engine.
I agree, I try to use distilled water, because most tap water will have minerals that can eventually cause issues... IMO, distilled water is cheap enough and easy to find...


Okay, we know Jim lives in Minnesota, and its gets cold... But while Anti-freeze has additives for lubrication and anti-freezing, straight water is a better "coolant". So depending on the air temps the car is stored at, you may not need to be 50/50...

Personally, here in California my garage never gets below 40 degrees. so I run no anti-freeze in my Chevelle (stored during the winter anyway)... I use Redline Water Wetter for the lubrication and surfactant additives...

Once you go RAT, you never go back...
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post #7 of 7 (permalink) Old Feb 25th, 19, 8:43 PM Thread Starter
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Re: Should I flush my old Mark IV or just replace coolant?

I try to run less coolant and more water in the summer. But late each fall I have been testing to determine how much I should drain and adding coolant. Garage is heated and furnace has never failed me. With -30 you canít be to safe with a unattached garage.


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