I purchased my '07 3.8 series in 06/2022. I had 36k on it. That winter, I had heater problems, I fixed it by back flushing the heater core. The next summer, I decided to do a cooling system flush, figuring it had never been done. I used Prestone cleaner, distilled water and Prestone Dexcool. Everthing was fine, except I was getting a build up of sludge in the radiator neck and cap. I would clean it good and replace it. I would have to do that every couple of weeks. The system has been pressure checked, and I had the oil analyzed, everythinh if good. This summer I want to do a very thorough flush and refill. My question is: Do I need to still use Dexcool, and how should I do this to get the best flush possible? Thanks!
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I would personally keep flushing it until it stays clean at that point before committing to the proper anti-freeze mix.
I'd drive around for a day or so with each fill then drain and repeat. Maybe with a decent splash of concentrated coolant in for water pump lubricity reasons
I'd drive around for a day or so with each fill then drain and repeat. Maybe with a decent splash of concentrated coolant in for water pump lubricity reasons
This is a picture of the radiator cap from your vehicle?
Yes. I have 2 so I can alternate while I clean them.
And it’s only been three years since multiple flushes and fresh coolant?
Is that oil milkshake on the cap?!?
Deathcool 
It's very hard to coolant flush a 3800 because draining the radiator with the drain cock only gets a gallon or so at a time, and it takes 3 gallons. The official GM method is to remove the knock sensors. If you want to do that, you need an oxygen sensor socket like this.
If you can access the knock sensors and do it that way, fill it with water and radiator flush. Then, let the car cool down before draining again and refilling with distilled water. Drive it some more, and a third drain and fill with water is optional, depending on how it looks. When you're finally ready to refill with coolant, use 1.5 gallons of Peak Titanium concentrate, then the rest with water.
Do you see any bubbles in the coolant reservoir? Any sign of a head gasket leak?
Have you ever replaced the coolant elbows? The OE elbows are plastic and prone to breaking, but there are aftermarket metal elbows to replace them with. If you replace the elbows, don't use the O-rings that come on them because they are poor quality. Instead, buy OEM O-rings to put on the metal elbows.
It's very hard to coolant flush a 3800 because draining the radiator with the drain cock only gets a gallon or so at a time, and it takes 3 gallons. The official GM method is to remove the knock sensors. If you want to do that, you need an oxygen sensor socket like this.
If you can access the knock sensors and do it that way, fill it with water and radiator flush. Then, let the car cool down before draining again and refilling with distilled water. Drive it some more, and a third drain and fill with water is optional, depending on how it looks. When you're finally ready to refill with coolant, use 1.5 gallons of Peak Titanium concentrate, then the rest with water.
Do you see any bubbles in the coolant reservoir? Any sign of a head gasket leak?
Have you ever replaced the coolant elbows? The OE elbows are plastic and prone to breaking, but there are aftermarket metal elbows to replace them with. If you replace the elbows, don't use the O-rings that come on them because they are poor quality. Instead, buy OEM O-rings to put on the metal elbows.
Closer to 2 years
I replaced the elbows when I replaced the water pumpDeathcool
It's very hard to coolant flush a 3800 because draining the radiator with the drain cock only gets a gallon or so at a time, and it takes 3 gallons. The official GM method is to remove the knock sensors. If you want to do that, you need an oxygen sensor socket like this.
If you can access the knock sensors and do it that way, fill it with water and radiator flush. Then, let the car cool down before draining again and refilling with distilled water. Drive it some more, and a third drain and fill with water is optional, depending on how it looks. When you're finally ready to refill with coolant, use 1.5 gallons of Peak Titanium concentrate, then the rest with water.
Do you see any bubbles in the coolant reservoir? Any sign of a head gasket leak?
Have you ever replaced the coolant elbows? The OE elbows are plastic and prone to breaking, but there are aftermarket metal elbows to replace them with. If you replace the elbows, don't use the O-rings that come on them because they are poor quality. Instead, buy OEM O-rings to put on the metal elbows.
You have a serious issue with your cooling system. Either this is oil in the coolant as someone has already noted, or there is some other serious issue. It’s not the coolant.
Last one I did like that I removed engine and pulled heads, freeze plugs, knock sensors and then flushed the block. I had radiator flushed at the radiator shop and replaces all rubber hoses along with plastic ones. New thermostat as well. I ran water through the heater core however it didn't hold pressure and wound up replacing it as well. I hated the job as it was extended warranty and was supposed to be leaking water pump. 10 year coolant looked like this in half that time. You never forget jobs like this.
How hard is it to remove the knock sensors? I am having radiator flushed next week at a shopDeathcool
It's very hard to coolant flush a 3800 because draining the radiator with the drain cock only gets a gallon or so at a time, and it takes 3 gallons. The official GM method is to remove the knock sensors. If you want to do that, you need an oxygen sensor socket like this.
If you can access the knock sensors and do it that way, fill it with water and radiator flush. Then, let the car cool down before draining again and refilling with distilled water. Drive it some more, and a third drain and fill with water is optional, depending on how it looks. When you're finally ready to refill with coolant, use 1.5 gallons of Peak Titanium concentrate, then the rest with water.
Do you see any bubbles in the coolant reservoir? Any sign of a head gasket leak?
Have you ever replaced the coolant elbows? The OE elbows are plastic and prone to breaking, but there are aftermarket metal elbows to replace them with. If you replace the elbows, don't use the O-rings that come on them because they are poor quality. Instead, buy OEM O-rings to put on the metal elbows.
If you have the oxygen sensor socket, the removal itself isn't the most difficult thing. It's a long, narrow path to the knock sensor. The rear one in the transverse versions is the hardest to access.
The real challenge is removing the knock sensor without damaging it
It has a tapered pipe thread and some kind of sealant. You have to do it with the engine cold, or it might not come off undamaged, if at all.
Most shops won't remove the knock sensors. They just flush it somehow.
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Dexcool does it again!
Dexcool is good coolant, but only if it gets changed regularly, and only if the cooling system never ever has any sort of leaks or air in the system.
What I would do is flush the cooling system with how ever many gallons of distilled water until it drains somewhat clean. Then get a bottle of Thermocure Evaporust, and distilled water and dump the Thermocure and water in the radiator. Drive it for a week, then drain the cooling system. Open the radiator petcock and also remove the lower radiator hose to get as much coolant out of the block. Also consider flushing the heater core with distilled water and a funnel.
Then flush the system with at least 12 gallons or more of distilled water, until what drains out looks like clean water.
Then use Prestone Max coolant with distilled water. Do not ever introduce any tap water or regular bottled water into the cooling system, not even a drop.
And just as a good measure, drain the radiator every 3-4 months and fill it with the coolant, until the coolant looks clean and new every time you open the radiator cap. This will make sure all the dirty stuff is out of the system, and you’ll never ever have problems again.
Dexcool is good coolant, but only if it gets changed regularly, and only if the cooling system never ever has any sort of leaks or air in the system.
What I would do is flush the cooling system with how ever many gallons of distilled water until it drains somewhat clean. Then get a bottle of Thermocure Evaporust, and distilled water and dump the Thermocure and water in the radiator. Drive it for a week, then drain the cooling system. Open the radiator petcock and also remove the lower radiator hose to get as much coolant out of the block. Also consider flushing the heater core with distilled water and a funnel.
Then flush the system with at least 12 gallons or more of distilled water, until what drains out looks like clean water.
Then use Prestone Max coolant with distilled water. Do not ever introduce any tap water or regular bottled water into the cooling system, not even a drop.
And just as a good measure, drain the radiator every 3-4 months and fill it with the coolant, until the coolant looks clean and new every time you open the radiator cap. This will make sure all the dirty stuff is out of the system, and you’ll never ever have problems again.
The use of tap water is dependent on the source. When I lived in the City of Milwaukee the municipal water was extremely low in minerals and was acceptable. Here in the suburbs, not at all.
But DI, RO or distilled is the safest route. There’s no reason to unnecessarily load the chelation agents in the coolant.
