"Sludge" in the cooling system XK 120

Recently I had to remove the radiator as a needed (better) access to the Steering Box. The engine has been completely rebuilt as was the radiator. Everything in the “water ways” was absolutely clean. I used a glycol based anti-freeze mixed with distilled water (50/50)

The engine only run for 15 minutes so far, just to check whether I made any mistakes. It runs perfect!

After having removed the radiator + hoses, I found some sort of “white/green” particles (possibly even some sort of crystals) in various places like the top hose. See photo of the Otter switch housing as an example.

What is this “sludge”? Would it disappear if the engine would run for a longer period at the right temperature? Should I replace the glycol based anti-freeze? It seemed the most “neutral” solution at the time…

Bob K.

I would remove the thermostat, and either put in that hole or put the thermostat housing back on such that you could insert it, and do a power flush. This is the tool you need for that.

ABN Automotive Coolant Flush Machine - Air and Water Combo Coolant Backflush Gun - Multi-Size Nozzles Fit 19-40mm Hoses

Do it in both directions, in the engine, and backflush the radiator (bottom to top).

It’s for this reason and others that I have a sock (actually the foot of an old pair of Jan’s pantyhose) placed inline in the upper coolant hose. And no, my car doesn’t run any hotter because of it.

Looks like aluminum oxide, could also be oxide left overs in head of inlet manifold.
When there was left over moisture and no coolant, aluminum crystals will form inside.

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Thanks for your advises, but I’m still curious what this white stuff actually is.The cooling fluid is otherwise absolutely clear with no rust nor other particles: it’s just that white material.

I will flush the system once more and the radiator is already out of the car, so no problem.

Just checked whether this white stuff would dissolve in (hot) water and it actually does, meaning it probably is some form of glycol.

Bob K.

Hi Bob,

Possibly just a mixture of Calcium carbonate and aluminium compounds (oxides). I would not be very worried about it, i had it in all my aluminium engines to a higher or lesser degree independently of the water used (deionized or tap). Reading that it dissolves in water could simply mean its an agglomerate, indeed held together by a glycol compound or a coumpound of glycol decomposition.

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Those particles of aluminum oxide were possibly clinging to inaccessible surfaces in the head and intake manifold by introducing fresh coolant the corrosion inhibitors may have begun to do their job and released them.

As others have noted, the white stuff is most likely aluminum based compounds flushed from the interior of the cylinder head. Green stuff usually indicates copper compounds, which most likely means it originated in the radiator.

Thank you to all that answered my question. I will flush the complete system and radiator once more. Apparently not something to worry about.

I cleaned the cooling system in first instance as best as I could but apparently after 20 years of standing somewhere in a shed without any fluids in the engine, these kind of things might happen.

Bob K.