Coolant Change - Overflow Tank Crud

[ZeeOSix]

Did the 2nd coolant change on my 2005 Toyota Tacoma (4.0L V6) today. The overflow tank is integrated in to the fan shroud, so it can't be removed to clean, but does have a rubber plug over a drain nipple on the bottom of the tank. I didnt drain the tank during the first coolant change 7 years ago.

I noticed quite a bit of "sediment" in the bottom of the tank this time, so I drained the tank this time, then used a waterpick to blast everything loose and flushed the tank many times with distilled water. I collected the drained and flushed tank fluid, then filtered it through a coffee filter to collect the sediments for inspection.

This was the result, it looks and feels like light tan "mud". Didn't really feel "gritty" at all between my fingers, more like smooth "mud".

So is this remnants from the engine casting, or from where? The inside of the cooling system looked like new, no sign of any corrosion. The old coolant drained from the radiator and engine looked clean, like it was still new, and had no sign of this sediment.

 

[Skippy722]

Could be the binder from the casting process, but that means they left a chunk of sand in the engine somewhere... the sand would have settled to a low spot somewhere in the engine, radiator, and/or heater core.

 

[ZeeOSix]

For some reason it only seemed to collect in the bottom of the overflow tank. Like it was light enough to flow around the coolant system and get siphoned over time through the radiator cap into the overflow tank from many repeated cold-hot-cold engine cycles.

 

[Mad_Hatter]

Could it be something from the coolant like silica, that precipitated??

See if Blackstone can analyze it..

 

[ZeeOSix]

The coolant in this truck since new, and used for the 1st coolant change, was the Toyota pink "super long life" coolant which I think doesn't have any silicate in the formulation.

 

[demarpaint]

It could be casting sand that found its way into the recovery tank. It could also be a ginger base cooling system stop leak. Many automakers use it on the assembly line to stop potential leaks due to dissimilar metals during the break in period.

Chrysler had a big issue with this a few years back with many of the 3.6L Wranglers. They also had issues with HOAT and OAT being mixed in the cooling system.

 

[Skippy722]

Originally Posted by demarpaint
Chrysler had a big issue with this a few years back with many of the 3.6L Wranglers. They also had issues with HOAT and OAT being mixed in the cooling system.

Yep... why it looks orange looking through the reservoir, but purple if you look straight at the liquid is beyond me though

 

[Linctex]

I don't think it's casting sand.

White aluminum oxide powder (corrosion residue) would be my first guess.

 

[ZeeOSix]

Originally Posted by Linctex
I don't think it's casting sand.

White aluminum oxide powder (corrosion residue) would be my first guess.


I thought of that, but the sediment is light brown and not white like I'd expect aluminum oxide to look. I'm letting it dry out to see if the color changes.

Inspection of the inside aluminum core of the radiator shows no visual signs of any corrosion. The drained coolant was just as clear as new coolant. Here's a photo of the drained coolant.

 

[Kestas]

Originally Posted by ZeeOSix
... but the sediment is light brown and not white like I'd expect aluminum oxide to look.

In my experience it takes very little iron oxide to stain something brown.

 

[ZeeOSix]

I'm wondering if what I found in the overflow tank was something caused by the coolant in the tank always being in contact with air since this overflow tank is not pressurized, but vented to the atmosphere.

If it came from inside the cooling system, it had to be light enough to get carried through the system and then collect in the top of the pressure cap neck on the radiator and get transferred to the overflow tank with repeated heat and pressure cycles.

 

[Lubener]

Many car makers throw a sealing tablet in the cooling system during manufacturing.