Cooling System

Wtreads1948

My '07 Lacrosse 3.8 just turned 90k. It developed a very small leak, which turned out to be the front heater hose elbow. I replaced both elbows and the water pump, which looked trashed, all of the vertcle fins were gone. Before tearing it apart, I did a complete flush. After I got everything back together, I filled it with antifeeeze, (50/50 Prestone dexcool approved and distilled water). After running the car for a while, everything looked good. When I checked it the next morning, I found the radiator filler neck was full of redish brown very thick sludge. I cleaned it out, made sure the radiator and overflow tank were full. The next morning, I checked it again, same thing. The engine is running great with no leaks. I did notice, using my scanner, that the temp isn't going over 187, It has a 192 stat. Also, hoses collapse after engine cools dowm.


Any idea what that sludge is and how do I get rid of it? Thanks!

thecardoc3

Dexcool antifreeze breaks down in the presence of air and this is the kind of deposits left behind by failed coolant. That debris is some of the additives in the coolant that have fallen out of suspension combined with material that was worn away due to the coolant's Ph level dropping too far, (turning more acidic) and also from the coolant no longer being able to protect components from cavitation. The water pump impeller damage is classic wear from both cavitation, and the continued circulation of the debris from it being worn away. This would have started long before the work that you did so there has to have been a problem that was undiscovered for six months to a year earlier.

The problem now is these deposits are everywhere in the system. In the block, the radiator, the heater core and it's going to seem like no amount of flushing will fully repair this issue. The engine block is the most difficult to address. You would need to remove the soft plugs and while flushing use a stiff wire to scrape the debris loose from the bottom of the coolant jacket. Even then you won't be able to reach everywhere but you would get most of it out that way. The heater core and radiator could just be replaced unless you want to have someone take the radiator apart and clean it which costs almost as much as replacing it.

There is another solution, but it does take some time. You can get an external coolant filter assembly that goes into one of the heater core hoses. You will find these common with large trucks but there are some smaller versions. This will overtime trap all of the debris that comes loose and you will just have to keep replacing the filter when it gets restricted. The thing is, if you don't stop this crud from circulating, it will cause erosion of every part that the coolant comes into contact with causing more leaks, and more circulating debris.