: How to properly do a Coolant Flush?

12-22-10, 02:10 PM
I drive a 2005 STS V8 1SE. Per the owner's manual the coolant needs to be changed every 100K/5 years. Well, I am only at 32k but at the 5 year mark.

I searched the forums and didn't come across anything yet.

Is this something you guys recommend doing? Anybody know how to do it? Any pics/diagrams?


12-22-10, 02:56 PM
Drain and fill would be easiest. There should be a petcock on the side rad tank, use that to drain the rad then fill with 50% straight Dex and 50% distilled water. You'll be there for days trying to get it all out but a simple drain/fill is fine.

12-23-10, 12:02 PM
Is the 50/50 mix STRICT for the STS? I have read others will flush distilled water through the system to get rid excess sediment. Sounds like a good idea, but the downside is not all the water will escape. Thus, you technically throw off the 50/50 mix when you go to refill.

Any thoughts?

12-23-10, 07:09 PM
You'd have to measure what you drain to ensure a 50/50 mix. 60% Dexcool provides the coldest protection. More than that actually reduces protection (if I remember right.)

I specified 50/50 when my dealer replaced the waterpump at about 55,000.

12-25-10, 06:36 AM
I was toying with the idea of changing the coolant mysef but my dealer gave me a price of, I believe around $135, and since it included drain, flush and refill, I went that route. Just a drain and fill is going to leave a substantial amount of old coolant in the system.

12-26-10, 05:32 PM
Manual says 13.0 quart coolant capacity. Can anybody verify this?

Is air in the system going to be a problem for a drain and fill? Does our car have a way to prevent/remedy this?

12-26-10, 11:56 PM
The manual is right. I haven't had any trouble with air in the system after the dealer replaced the water pump and did the flush & fill.

12-27-10, 11:34 PM
I tackled it this afternoon, and it went very well. The dealer's option of $140 doesn't sound that bad in retrospect. But for those who want to save a few $$, here is how I did it.

The STS V8 has a 13.0 quart coolant capacity. The petcock from the radiator drains approx 6 - 6.5 quarts. This leaves 6.5 quarts of old coolant in the engine block. So, a simple drain and fill won't work. What you have to do is somehow get 13 quarts of pure water into the system so when you drain the petcock you are left with 6.5 quarts of water. You top off with 6.5 quarts of pure DEX and you have your 50/50 13 quart mix.

To get pure water in the system, I did the following:
1.) Drain using the petcock (approx 5.5 quarts + 1 quart that spills on the driveway no matter what you do)
2.) Fill coolant reservoir to the full line with distilled water (approx 6 quarts)
3.) Turn engine on with heater set to 88 deg, let idle for approx 5 minutes
4.) Drain using the petcock

Repeat steps 1-4 until what you are draining is clear. You can do this as many times as you want, but it took me about 5 times.

I attached some pictures for reference. A few things to keep in mind:
- The petcock drains everywhere, so have about 4 or 5 catch cans ready at different spots to get accurate drain measurements.
- On the last fill, it took about 5.5 quarts of DEX to the fill line. I drove around for a few minutes, got the 'Check Coolant Level' on the DIC, returned home and topped off with 1 quart of DEX for my desired 6.5 quarts.

It took me a few hours to do. Total price was around $30 (2 gallons of DEX plus about 10 gallons of distilled water). I liked doing it myself not only for the savings, but also to guarantee it was a complete flush of the old stuff.

There could be other ways, but this way worked for me. I hope it helps you, too.

12-28-10, 11:10 AM
How did the liquid look that you drain from the engine? Were there a lot of sediment or rust in the liquid in you catch can, looks clean to me. What do you accomplish by changing the coolant on a close system????

12-28-10, 12:56 PM
On my 2000 STS there where some tables that you had to put in the lower radiator hose. I think to help keep the head gaskets pliable. Is this not required on our generation of STS Ns????

12-28-10, 05:10 PM
turnerbend - The old coolant was pretty much free of sediment. I noticed some, but very very little. I changed the coolant per the owner's manual recommendation since I am at the 5 year mark with my 2005.

The cooling system in your vehicle is filled with
DEX-COOLŪ engine coolant. This coolant is designed
to remain in your vehicle for 5 years or 150,000 miles
(240 000 km), whichever occurs first, if you add
only DEX-COOLŪ extended life coolant.

Greg00coupe - I didn't add any tablets. Manual says not necessary.

Use a mixture of one-half clean, drinkable water and
one-half DEX-COOLŪ coolant which will not damage
aluminum parts. If you use this coolant mixture, you do
not need to add anything else.

Notice: If you use the proper coolant, you do not
have to add extra inhibitors or additives which claim
to improve the system. These can be harmful.

The manual also says to use clean, drinkable water. I used distilled. Hopefully it doesn't make a big difference.

12-28-10, 06:56 PM
The manual also says to use clean, drinkable water. I used distilled. Hopefully it doesn't make a big difference.

"Clean, drinkable water" can have minerals, chlorine, etc. I would not use tap water in my car's coolant system. I don't drink it either. You done good!

12-28-10, 09:30 PM
On my 2000 STS there where some tables that you had to put in the lower radiator hose. I think to help keep the head gaskets pliable. Is this not required on our generation of STS Ns????

Those tablets are Stop Leak! The N* was perfected when it was redesigned for RWD. Before that, not so much (IMHO).

02-01-11, 03:17 PM
Just bought a 99 SLS and was looking at the coolant and it appears a little nasty. I am considering taking it somewhere just because it cold outside and I have a very small garage to work in. In other forums I have heard many recommendations to get rid of dex-cool coolant and just go with the standard green stuff. The was not for any specific car but just GM in General. Does anyone have any though, comments, experiences, or recommendations on this? I'm surprised that I have not come across anything about this yet.

Any help is appreciated.

02-01-11, 08:30 PM
I'm sticking with Dexcool. You might consider checking out the Northstar or Seville forums to get a feel for what other owners of your year/model car think about it.

02-02-11, 08:34 AM
I can only tell you of my experience with Dexcool. I have had Dexcool in four vehicles and used Dexcool as a replacement coolant in my motorcycle (FJR-1300) and have never had any coolant systems problems. While seemingly there have been multiple Dexcool problems reported, out of the millions of cars that have had Dexcool installed, the number of issues is relatively small (and perhaps the correlation to Dexcool is coincident and unfounded); my last statement is jmo and conjecture on my part.

02-02-11, 08:08 PM
Some earlier formulations of Dexcool generated more reports of trouble than expected. Many seem related to the possibilty of contamination by air. Later formulations seem more stable. I now use it without any worry.

But all coolents are better than ever. Just don't go cheap; use a good quality coolent and change it as recommended.

02-04-11, 02:41 PM
I am against switching from orange to green. Stick with what your car came with. It says all over the labels to not mix the two. I honestly believe people ran into problems with DEX cool because they tried adding it to their car without first completely draining all of the green.

From personal experience, I have Dex cool in both my 05's and have had no problem with my cooling system. On the same note, I had green in my '97 mitsu and had no problems with the cooling system. My advice is to stick with what the car came with.

02-06-11, 08:22 PM
Checked on two sources:
One is my buddy, who works for Dealer #1, he told me they have a machine
to do a coolant flush.
The Other is: I went to a closer Cadillac Dealer #2, and the service manager
told me, they have a Machine that recircs the coolant thru the engine ?
They get $ 169.00 for a coolant flush.
Also asked about the transmission fluid replacement, they get $ 199.00,
for that, he also told me they service the local Police dept, and do service on
them every 30,000 miles,and the vehicles last longer than those who wait
the required mileage before doing certain maintenance stuff.
My owners manual says to wait 100,000 for transmission fluid change.
I am going to get it changed @ 50,000. :cool2::cool2:

Testing: Castrol EDGE, 5W-30 and the M1 oil filter, with anti-drainback
valve. Feel a lot better knowing I won't be doing Dry Start, Startups !

02-07-11, 09:02 PM
I would not be real concerned putting a machine on a cooling system but the old-fashioned methods of reverse flushing with a hose is likely just as good as any machine. (Just make sure to get it up to operating temperature a few times with the heat on maximum to flush the heater core.)

I would be VERY HESITANT to put a machine on my STS transmission. More than half the time, the last transmission serviced on that machine had a worn out or failing transmission and that flush was a 'last resort' before a rebuild. Our cars have very intricate transmissions assembled in 'clean room' conditions. I would want assurances that the flushing machine was completely clean and a guarantee before I'd even consider doing so. What is the shop manual's procedure?

Besides, transmission fluid (hydraulic oil with specialized additives) doesn't get exposed to combustion or dirt like engine oil. If the car is well treated, it doesn't even get all that hot. Unless I find reason to believe it needs early service, I'm waiting to 100,000 miles as stated in the manual.

But it's your car...

02-27-11, 08:51 PM