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Discussion Starter #1
I am curious about the water/coolant mix in my antifreeze. The coolant was changed right before I purchased the car. I have one of those cheap Prestone antifreeze testers to check freeze and boil over protection. Can I pull the coolant sample from the expansion tank in my 01 Deville and get an accurate reading? Is the coolant in this tank regularly circulated through the engine? (I'm assuming so, since the coolant in the tank is nice and hot).

Also, I have noticed the coolant is a light brown color instead of pink. I know the dealer said he put in the GM Sealing Supplement which seems like it would change the coolant color to brown.
 

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You can check accurately from the overflow tank, as long as the coolant is mixed thoroughly. If all was added premixed at 50/50 your good to go for checking it. The tank get circulated as part of the entire system. I'm not sure on the brown color, but the supplement is the likely cause.
 

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White Diamond '03 DHS (with DTS floor shift)
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Can I pull the coolant sample from the expansion tank in my 01 Deville and get an accurate reading?
No. You'd need a refractometer.

Is the coolant in this tank regularly circulated through the engine?
Yes.

A
lso, I have noticed the coolant is a light brown color instead of pink. I know the dealer said he put in the GM Sealing Supplement which seems like it would change the coolant color to brown.
Yup, that's from the supplement.
 

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Cadillac Technician
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As Ranger said, a refractometer is the most accurate, but it is also quite expensive.
Using a cheapo tester is usually accurate enough to give you an idea of your protection but if you live pretty far North you might want to see if you can find a shop that has a refractometer.
http://www.thetoolwarehouse.net/shop/ROB-75240.html
Not quite as pricey as I thought, heck I might buy one!

In most US climates that don't see temps as low as zero a ballpark reading is pretty good.
The "seal tabs" will darken the coolant.

The coolant is regularly circulated through the overflow.
 

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Discussion Starter #6
Thanks for the detailed advice. I travel pretty far north, and my former vehicles have seen temperatures down to -40F. My cheap anti-freeze tester indicates close to a 50/50 mix. I'll switch to a 70/30 mix when winter hits.
 

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White Diamond '03 DHS (with DTS floor shift)
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50/50 should be good for close to -40 I think. I wouldn't go 70/30.
 
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