Last summer, I changed out the timing belt and associated components in my new-to-me 2002 Audi Allroad with the 2.7 twin turbo motor. I noticed that the coolant, while the proper pink color, was milky. Not oily milky, but more like sediment milky.
I didn't really give it another thought. At the end of the job, I put in 3 liters of Pentosin G12 and filled it with distilled water.
A few weeks later, on a road trip, I got caught in rush hour traffic in 100-degree heat for about an hour. The coolant temp came up one tick mark above usual, but less than 3/4 on the gauge. When I got to my destination, I opened the hood to let some of the heat out. To my surprise, the coolant was not pink, but rather a pale beige. Light tan. It was far too hot to open it up, so I waited until it cooled off. The next morning, I popped the hood open and the coolant is now pink again. Weird. Internet searches for coolant changes color bring up nothing.
A couple weeks later, we got our first cold snap, and I have no heat. I mean none. So plugging "no heat" into google gets me pages about coolant flushes. I decide on the wood bleach/washing soda flush and after much dithering, I finally get around to it.
After running the acid solution for 3 hours, I remove what I think is the drain plug at the back of the engine, and nothing happens. Then a drop. Then another. Then boiling coolant erupts out of the drain with a vengance. There was so much scale in the cooling passages that hot coolant under pressure actually had to think about it for a while before making it out the drain.
The crud that came out is hard to describe. It looked more like the color of used motor oil (not viscosity, mind you, just color) than like any coolant I've ever seen. Black, chunky and cruddy.
After this, the heat starts to work a little bit, but the coolant keeps losing its color and sediment builds up in the coolant tank. So a couple weeks later I do another heavy duty oxalic acid flush. Again ugly as sin.
Now the heat works fine, but the coolant keeps crudding up. Just for the sake of variety, I switch to citric acid and do two complete cycles of: Dishwasher soap, water, citric acid, water, washing soda, water. When I say "water" I mean running the hose through the cooling system with the drains and vents open and engine idling for 15 minutes at full flow with water coming out all the openings. Hundreds of gallons total.
The after-run auxiliary coolant pump, which is on a thermal switch, now runs almost every time I shut it down from normal operating temperature, where before it never ran. Good, I guess, but a little odd.
Now there's no more sand, mud, or lime scale, but I have big black flakes floating around in the coolant. By "big" I mean up to 1"x2" in size. They look like something scorched. Maybe like when you burn the soup and try stirring it up instead of just pouring off the unburned part. They're slightly sticky when wet, and they get crispy and brittle when they dry.
So, any idea what these might be? One that I have on my desk looks like it might have been formed on the outside of a torus (donut-shape) that's about 3" in diameter and 1/2" thick.
I'm thinking turbos because they're the hottest part of the cooling system, as far as I know, but it could be from anywhere. Maybe a turbo housing cooling channel? Maybe one of the flush products got heated up to the point it accreted onto the wall of the turbos? I don't know much chemistry, would oxalic acid, citric acid, dishwasher soap, or washing soda scorch a residue like this?
I didn't really give it another thought. At the end of the job, I put in 3 liters of Pentosin G12 and filled it with distilled water.
A few weeks later, on a road trip, I got caught in rush hour traffic in 100-degree heat for about an hour. The coolant temp came up one tick mark above usual, but less than 3/4 on the gauge. When I got to my destination, I opened the hood to let some of the heat out. To my surprise, the coolant was not pink, but rather a pale beige. Light tan. It was far too hot to open it up, so I waited until it cooled off. The next morning, I popped the hood open and the coolant is now pink again. Weird. Internet searches for coolant changes color bring up nothing.
A couple weeks later, we got our first cold snap, and I have no heat. I mean none. So plugging "no heat" into google gets me pages about coolant flushes. I decide on the wood bleach/washing soda flush and after much dithering, I finally get around to it.
After running the acid solution for 3 hours, I remove what I think is the drain plug at the back of the engine, and nothing happens. Then a drop. Then another. Then boiling coolant erupts out of the drain with a vengance. There was so much scale in the cooling passages that hot coolant under pressure actually had to think about it for a while before making it out the drain.
The crud that came out is hard to describe. It looked more like the color of used motor oil (not viscosity, mind you, just color) than like any coolant I've ever seen. Black, chunky and cruddy.
After this, the heat starts to work a little bit, but the coolant keeps losing its color and sediment builds up in the coolant tank. So a couple weeks later I do another heavy duty oxalic acid flush. Again ugly as sin.
Now the heat works fine, but the coolant keeps crudding up. Just for the sake of variety, I switch to citric acid and do two complete cycles of: Dishwasher soap, water, citric acid, water, washing soda, water. When I say "water" I mean running the hose through the cooling system with the drains and vents open and engine idling for 15 minutes at full flow with water coming out all the openings. Hundreds of gallons total.
The after-run auxiliary coolant pump, which is on a thermal switch, now runs almost every time I shut it down from normal operating temperature, where before it never ran. Good, I guess, but a little odd.
Now there's no more sand, mud, or lime scale, but I have big black flakes floating around in the coolant. By "big" I mean up to 1"x2" in size. They look like something scorched. Maybe like when you burn the soup and try stirring it up instead of just pouring off the unburned part. They're slightly sticky when wet, and they get crispy and brittle when they dry.
So, any idea what these might be? One that I have on my desk looks like it might have been formed on the outside of a torus (donut-shape) that's about 3" in diameter and 1/2" thick.
I'm thinking turbos because they're the hottest part of the cooling system, as far as I know, but it could be from anywhere. Maybe a turbo housing cooling channel? Maybe one of the flush products got heated up to the point it accreted onto the wall of the turbos? I don't know much chemistry, would oxalic acid, citric acid, dishwasher soap, or washing soda scorch a residue like this?
