Engine Coolant Change out
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Northstar Engines and System Technical Discussion Discussion, Engine Coolant Change out in Cadillac Engine Technical Discussion; Whats a good rule of thumb for changing engine coolant. And i dont use Dexcool. Just the green stuff. I ...
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    STS 310's Avatar
    STS 310 is offline Cadillac Owners Connoisseur
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    Engine Coolant Change out

    Whats a good rule of thumb for changing engine coolant. And i dont use Dexcool. Just the green stuff. I want to keep that head gasket happy!!!!!

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    JimD is offline Cadillac Owners Connoisseur
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    Re: Engine Coolant Change out

    Remove a hose or hoses and drain as much as possible (you won't get much more than half of it drained). Resist the temptation to flush with water because you will lose control of the desired 50/50 mixture.

    Place GM coolant supplement tablets or Barsleak Golden Seal powder in the hose and reinstall the hose. Refill with 50/50 antifreeze/distilled water.

    Repeat in 2 years/24,000 miles if you are using 'green' antifreeze.

    Jim (125,000 trouble free miles with Dex-Cool)

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    Geno Castellano is offline Cadillac Owners Fanatic
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    Re: Engine Coolant Change out

    Quote Originally Posted by SLS LUV
    Whats a good rule of thumb for changing engine coolant. And i dont use Dexcool. Just the green stuff. I want to keep that head gasket happy!!!!!

    You have a 97 and you don't use DexCool? That car came with DexCool so either it has DexCool in it or you switched it. If you switched it - why? DexCool is good for 100K/5 years. The conventional green silicated coolant is good for 24-32K/2-3 years. Both offer equal levels of corrosion protection so why switch from DexCool to the green stuff?

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    STS 310's Avatar
    STS 310 is offline Cadillac Owners Connoisseur
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    Re: Engine Coolant Change out

    It was evidently switched before i got the car about a year ago. I didnt check the coolant when i bought it. Actually i didnt check very many things at all just a visual, and a test drive(45 min!, I knew the dealer). 36k miles for almost a seven year car was really nice also!

    When i got an oil change a couple of months ago they said the coolant was fine. I never thought to ask what type it was. When i took the cap off a couple of days ago, i noticed it was green..... So i guess i stick to the green now.

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    formulacarracerjim is offline Cadillac Owners Member
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    Re: Engine Coolant Change out

    I'm not afraid to flush thru with lots and lots of water. Remove lower hose and surge tank lower hose. Drain all you can and then flush, flush and flush. Add pellets. Put back together. Check your coolant capacity, divide by two and add that much coolant. Top with distilled water, purge air tada! Jim

  7. #6
    Geno Castellano is offline Cadillac Owners Fanatic
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    Re: Engine Coolant Change out

    Quote Originally Posted by SLS LUV
    It was evidently switched before i got the car about a year ago. I didnt check the coolant when i bought it. Actually i didnt check very many things at all just a visual, and a test drive(45 min!, I knew the dealer). 36k miles for almost a seven year car was really nice also!

    When i got an oil change a couple of months ago they said the coolant was fine. I never thought to ask what type it was. When i took the cap off a couple of days ago, i noticed it was green..... So i guess i stick to the green now.
    I would stick with the green conventional coolant at this point. Use either Prestone or Texaco. Both were OEM suppliers of coolant of that type.

  8. #7
    Geno Castellano is offline Cadillac Owners Fanatic
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    Re: Engine Coolant Change out

    Quote Originally Posted by formulacarracerjim
    I'm not afraid to flush thru with lots and lots of water. Remove lower hose and surge tank lower hose. Drain all you can and then flush, flush and flush. Add pellets. Put back together. Check your coolant capacity, divide by two and add that much coolant. Top with distilled water, purge air tada! Jim
    There are several problems with this approach that have been discussed previously. I personally do not recommend this approach because:

    1. This introduces large quantities of tap water into the system that cannot be removed or eliminated. Tap water contains minerals that tend to neuter the corrosion inhibitors in the coolant and can cause particulate formation in the coolant causing deposit formantion. Depending on the area of the country and the source of the water the mineral content can be quit high and damaging to cooling systems. Tap water is definitely NOT recommended for cooling systems if you want to maximize the life of it. Distilled water is the only recommended water for cooling system to eliminate any possibility of mineral contamination.

    2. It is very hard to determine exactly how much water is in the system and then drain and fill with straight coolant to get the correct 50/50 mix... Just something that is not necessary. By just draining and refilling with fresh 50/50 mix you avoid this hassle and inaccuracy and eliminate any concerns about not having the correct mix or having to check with a test instrument. It is vital to have the correct 50/50 mix as it provides the most boiling protection for hot weather and the best freeze protection for cold weather. Since ethyleneglycol is more viscous than water adding more than 50% EG to the mix causes an additional loss of cooling efficiency due to the added viscosity and reduced heat transfer capability.

    Hydrometers for testing coolant percentage or coolant strength are notoriously inaccurate if you think that you can just add straight coolant and test the mixture. They are way off due to air bubbles sticking to the floating elements and temperature changes in the coolant changing the specific gravity which affects the reading. They can be 10-15% off in coolant percentage easily. If you doubt this, mix some perfect 50/50 coolant and test it with your favorite tester. Test the mix 10 times over a half hour and see how much the readings vary. Hydrometers are worse than useless....they are very misleading if you are depending on them to set your coolant concentration.

    If you must check the percentage of the coolant concentration find and use a refractometer.

    3. With the thermostat in the engine it is very hard to force coolant thru the engine when "flushing" with a garden hose. Especially with a Northstar stat that is on the cold side. It will close and nothing really goes thru the engine and heater core unless you disconnect the heater hoses and/or remove the stat. So the "flushing" with plain water just introduces tap water and really doesn't accomplish anything.

    4. Flushing and filling and measuring and draining and adding is a major pain and takes forever....so you put it off as a major job. If you simply drain and refill with fresh 50/50 coolant/distilled water it is an easy job, the concentration is never in doubt, you never have to check the concentration (if you mixed carefully) soo you tend to do a cooling system refresh more often since you can basically do it while you change oil. It's simple and easy that way so it gets done.

    About the only time I would condone flushing with a hose is when the sytem is hopelessly clogged due to lack of maintenance OR just flushing the heater core itself when/if the heater core is clogged due to lack of maintenance.

  9. #8
    90deville415 is offline Cadillac Owners Member
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    Re: Engine Coolant Change out

    Thanks so much for this information, Geno. I wouldn't even thought about changing the coolant if I hadn't read this. 1990 deville with 110,000 miles (I bought it a few months ago), it actually seems to be running better since I had the coolant changed out using distilled water. That's probably not possible, but either way I'm thrilled. I love this car and I'm so happy to have a way to make it last longer.

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