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Coolant flushing, burping and Low Coolant warning

42K views 12 replies 7 participants last post by  SlammedLLY 
#1 ·
2005 Duramax, 140K. Trucks been working fine since the day I got it 7 years ago. It's been slow to heat, and I haven't been getting as much heat as in the past, so I figured it was time for a bit of maintenance.

I changed the thermostats this morning, drained the cooling system, filled with water. Opened the bleeder until I got consistent water coming out. Ran the truck, drove a short distance. No heat. Came back, opened the bleeder, got lots of water/air mixture out for a few minutes. Drove it again. No movement on the temp gauge, no heat.

Suddenly, after a half mile or so, temperature jumped to just below the 210 mark and I had heat. But I ALSO had a "Low Coolant" warning on the DIC.
Back to home, bled again. No air came out, just coolant. Overflow tank is full to the "full hot" mark.

Out for another drive. Temperature fluctuates between the large mark below the 210 (maybe 180?), and just below the 210. And LOTS of heat.
But, I"m STILL getting the Low Coolant warning. I've stopped and started the truck several times.........

Truck is now sitting until tomorrow - just to see if anything changes after it cools...

WHERE does it get the "Low Coolant" indicator from? Is it on the overflow tank? Radiator? Somewhere else? And if, when I open the bleeder, I just get a solid stream of water, WHERE is it low on coolant?
 
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#2 ·
I dont know that this will answer your question, but when I did a coolant flush on my LLY, after I drained it all out, I filled back up through the overflow tank. The threw few gallons of coolant in the back (seeing that I had not put in as much as I took out) and drove the truck. You have to drive it long enough the allow the thermostat to open. For me, it was about 2 miles.
Did the same thing, the temperature was slowly rising, then instantly went to 210 and "low coolant" came on. I pulled over, added a gallon of coolant to where the line is. Drove it another couple miles, it did the same thing. So I added more.
After that it was fine. Ran at normal temps and never got a coolant low message, though i still did have to add a little more.

I never had to bleed mine...?
 
#3 · (Edited)
Sounds like your thermostats weren't working properly. Make sure to burp the air out of the system by opening the bolt on the thermostat housing. Once you get nothing but coolant, then just keep adding coolant to the overflow tank to bring it to full again and it should be good after that.
 
#4 ·
I don't know if this is BS or not, but when I had my EGR cooler replaced on my 05 a few years back, the dealer told me they had to do a vacuum fill of the coolant because the EGR cooler is the high spot of the cooling system and air would get trapped in it. They said if air was trapped in it, it would get too hot from the exhaust heat and be damaged.
 
#5 ·
Well, it took a day, and a couple short drives, but once things got to "normal" temperature, and a bit more burping and filling and driving and burping and filling, the "low coolant" warning went away and it's working great! It heats up TONS faster than it was before, and later this week I"ll dump all the cooling system flushing stuff and do the fill with anti-freeze.
 
#7 ·
Yeah, I put it on the hottest setting and also varied engine speed by staying in 3rd gear... After a half mile or so it suddenly jumped from no reading to just under 210...
 
#9 ·
is there a DIY on this...i wanna flush mine too, i know theres a drain somewhere in the front to flush it...after you finish flushing the coolant how do you know when all the water is out..is there a drain at the bottom of the cooling system (radiator) or something that drains everything in the cooling system
 
#10 · (Edited)
If you have an LB7/LLY then the drain is on the lower passenger side portion of the radiator. Open it slowly because there's alot of coolant in there and it will make a huge mess.....5 gallon bucket comes in handy here. If flushing with water, remove both the upper and lower radiator hoses as well. Once done, replace all hoses and refill with coolant through the reservoir with bleeder screw on thermostat open. Replace the screw once coolant begins to come out. Always make sure heater is open when refilling and check reservoir tank level, refilling as necessary.
 

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#13 · (Edited)
ok so draining the sysyem fully and refilling it with new coolant is sufficent enough...i bought the truck with 140k and now have 170k on it...not sure if the coolant has ever been changed but want to do it just to be sure..
how much coolant will i need to refill after opening up all the pockets and bleeding the air?
 
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