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1991 seville
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Discussion Starter #1
I just purchased a 1989 sedan deville with 111000 on it. The body is in perfect shape for being a northeast car. The last owner owned it for 21 years. I am trying to do all the fluids. There seem to be differing points of view as far as the cooling system. Do I: Just drain and refill? Drain and flush? Drain and flush with a flushing chemical? Is tap water ok, or does it need to be distilled? Green coolant? Tabs I am assuming need to be put in, how many, and do I just put them into the radiator as a whole tab or do I grind them up and put them in the upper hose?
Also, while I am at it, do you recommend a transmission fluid and filter change? Thanks in advance!!!
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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Standard all makes/all models green/yellow coolant can be used in any engine, and it was factory fill in yours.

The tabs are no longer used or recommended by GM. They're known to clog small coolant passages.

A flush isn't recommended or necessary unless you're trying to clean out a stop leak product.

Refill with a 50/50 mixture of coolant and distiller water. Tap and spring water has minerals in it that can cause corrosion.

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If the fluid doesn't appear as a bright, clear red on the dipstick, replace it. If it looks good, you can change it if you want, it will only do good. Personally, I tend to change trans fluid at ~80K, or whenever I buy a vehicle if it has more mileage than that.
 

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1991 seville
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Discussion Starter #3
I thought that you still needed to use the pellets on the 4.5/4.9?? I know these engines can go over 200,000 miles, I just want to make sure that I do the right thing.
 

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1991 Cadillac Sedan deVille
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591 Posts
You can use them if you like, but your heater core might get plugged up. They are no longer recommended, but if you decide to use them just be careful with the quantity. I still use them with no problems.
 

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White Diamond '03 DHS (with DTS floor shift)
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Color can be deceptive. Fresh new coolant will look old, "rusty" & muddy after adding the sealant tabs.
 

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1991 seville
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Discussion Starter #8
Ranger, I would love your opinion on this. This is what I am thinking of doing. Drain and refill, no flush. But...If I just drain it from the bottom hose, I will still have all the old stuff in the engine. Not sure how to get that out. I still think I am inclined to use the tabs, as there was a mentality when the engine was made that they were needed, and the cars have lasted this long with them, or possibly because of them. I just bought it, so I can't have the engine taking a dump in 10,000 miles.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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Your cooling system has nothing to do with the longevity of the rest of the engine. It keeps the engine at operating temp, nothing more.

The tabs were to stop nuisance leaks and possible porosity issues. They don't make the engine last longer. GM released a TSB stating not to use them any longer.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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If your coolant already looks sludgy, then you should have enough sealant tab residue and no more should be needed. I used to add only 1 or 2 tabs for peace of mind but it probably wasn't necessary because the coolant and radiator cap were already sludgy when I bought it. If the coolant is really clean and green, I would assume it was changed recently and leave it until the water pump starts leaking.
 

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White Diamond '03 DHS (with DTS floor shift)
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Ranger, I would love your opinion on this. This is what I am thinking of doing. Drain and refill, no flush. But...If I just drain it from the bottom hose, I will still have all the old stuff in the engine. Not sure how to get that out.
Drain it from the radiator drain plug. That'll be the lowest point in the system and the point where you'll get the most out of it. If you want to get fanatic and try to get a little more, reverse the flow of your shop vac (assuming you have one), stick the nozzle in the radiator neck and seal it as best you can with a rag. That'll blow out some extra residual coolant.

I would just drain & refill and I would not use the sealant tabs myself. If it's made it this long with no leaks, there probably ain't any that the tabs are going to help.
 

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1991 seville
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Discussion Starter #13
So, just drain what I can get out of the radiator out, don't worry about a flush, or what is left in the engine and put 50/50 back in? Thanks for all the thoughts on this!!
 

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Keep in mind, IF you flush it, you'll have residual water left in it and you'll then have to calculate and compensate to get back to 50/50. The choice is yours, but I don't think a flush is necessary (unless it's never been changed).
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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Again, I'd suggest a simple drain and fill, repeat every 2-3 years.
The whole point of changing the coolant is to replenish the anti corrosive additives. Draining and filling does exactly that.
 

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1992 DeVille
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Ranger said:
Keep in mind, IF you flush it, you'll have residual water left in it and you'll then have to calculate and compensate to get back to 50/50. The choice is yours, but I don't think a flush is necessary (unless it's never been changed).
It's near impossible to get it exactly 50/50 too. Simple drain and refill is the easiest

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seville1991 said:
So, just drain what I can get out of the radiator out, don't worry about a flush, or what is left in the engine and put 50/50 back in? Thanks for all the thoughts on this!!
Yeahp!
 
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