In the past i used the MoCool of Motul, the idea was to help my car in hard city traffic conditions to don't get overheated. In the past years i had used similar products as W.Wetter, Royal Purple and i had no problems.

Turning back the time i remember that i had a problem with my water pump gasket (this means change of coolant) plus few months latter a thermostat problem (change of coolant also) so i ended-up with 2 brands of G11 Antifreeze in my car because when the 2nd incident happened i was travelling so i could find the same.

Those 2 coolant changes made the analogy to be very wrong, maybe i was 60-70% Antifreeze and the rest distilled water and i added the MoCool without taking proper measurements before, if i had done this i could see that my coolant was more thick (more ''strong" s we say it here in Greece).

 

I extract some of this ''coolant mix" (blue colour both) and i added MoCool (blue colour) according to the label on the bottle, after few days on city traffic everything looked good (1-2 'C lower temperature) but soon this stopped and when i opened the cap to make a volatilization i was shocked!

The expansion reservoir has full of black ''sludge" and the coolant was black, it was some kind of chemical reaction and i was terrified because i thought that this sludge would be stuck in my water pump blades, my thermostat, it's sensor, in the wall of the hoses etc.

 

 

 

 

 

 

 

 

 

 

 

 

I said ''OK, this is the End of my whole coolant circuit"   and i had to remove and clean everything which means time and lot of money.

 

 

 

 

 

 

fill with distilled and add coolants flush

Correction: The Motul MoCool has bordeaux (is US call it burgundy) colour and not blue as i wrote.

 

@Thefeliciahacker : Although was sort of sticky i didn't show any marks on the thermostat sensor when i removed him, it was very clear. Also with my finger i didn't felt anything on the thermostat itself nor the cap which also was no sticky. The weird thing was that i didn't had any overheating signs and the digital gauge below expansion reservoir was working normally.

The whole situation remind me the lathe and the bubbles when we cook in a pot, when the water is boiling close to 100 'C they stick to the walls, here is an example:

 

 

 

I will post some photos more from inside the plastic reservoir.

Could this be residue from previous coolant fills and drains lifting to the surface now?

 

Many drains are done cold and quick, leaving a lot of existing coolant and contaminants still left in the system, often draining the engine block (and heater matrix) are forgotten or ignored leaving even more residue in the system.

 

Have you fitted anything new recently with rubber, for many years with classic car parts we had/have ****-poor rubbish rubber in many parts and components that would craze or split within months and weeks (and even days) of being fitted.

 

I had a clutch concentric slave cylinder that was manufactured with the wrong type of rubber seals and it broke down and caused a leaked and ever since then despite having the seals replaced by the manufacturer, the clutch system as a whole holding very little fluid and flushing through on various occasions about 2 litres of fluid whilst at the same time cleaning the inside of the reservoir, the reservoir is black coated inside within days of use again.  This is despite also last time replacing the master cylinder - but this might cause more black if it seals also give off black, but I do not know.

 

When the clutch concentric slave cylinder seals broke down (which is an engine out to replace seals) I could clearly see with even my poor eyesight fibrous particles floating in the fluid so I knew it was the seal.

 

I have no idea what they do to make these cheap rubber parts but I had a fanbelt (drivebelt) from a reputable specialist classic car parts supplier that looked like the black colour and smell to it had ben added or leached through, it marked my hand and stunk the shed out, I threw it away and replaced it with a Gates belt.

 

If you have no freezing temperatures I would do as TheFeleciahacker has put and then go further with cycles of draining and refilling with just water for a day or numbers of days car use and repeat until you are sure it is clean.  Do not add any anti-freeze, coolant or coolant additives just water to cycle flush clean any anti-freeze, coolant or coolant additives that were stuck inside.  Repeat the clean water flushes a few times before the final refill of antifreeze (and additive).

 

I have simple but thorough method(s) of cleaning the cooling/heating system but it is best done in warmer weather and you need access to a running water hose of suitable mains or gravity pressure (not too low or too high).

 

Scooping some of the coloured lather and froth  and putting it on a white paper towel  may how you more, same with the black residue in the reservoir and on the end of the reservoir attached tubes.  You may be able to tell if there is more than one thing in the black stuff or just perhaps a chemical reaction of anti-freeze, coolant or coolant additives.

 

Edited 27 February, 20224 yr by nta16
spelling

33 minutes ago, nta16 said:

Could this be residue from previous coolant fills and drains lifting to the surface now?

 

No, for all these years i have never-ever saw a phenomenon like this, only after the installation of MoCool additive and after few days my expansion reservoir looked like had liquid tar inside.

I was terrified, i though that everything in my coolant system had this black sticky substance, water pump-thermostat-sensor-hoses etc i thought that all would be covered and this meant a fortune from me for repair.

 

 

 

 

 

 

 

 

 

 

 

Here are two older examples, one from 2019

 

 

 

and one from late 2021

 

 

 

Everything fine, blue colour and the reservoir plastic tank was clear and may times i have checked the interior.

The MoCool chemically reacted with those 2 Antifreeze blends and then...came the mess!

1 hour ago, D.FYLAKTOS said:

No, for all these years i have never-ever saw a phenomenon like this,

No I was thinking of your more recent fills of the cooling system.

 

 

1 hour ago, D.FYLAKTOS said:

one from 2019

So very clean.

 

 

1 hour ago, D.FYLAKTOS said:

Everything fine, blue colour and the reservoir plastic tank was clear and may times i have checked the interior.

The MoCool chemically reacted with those 2 Antifreeze blends and then...came the mess!

So it was all with the additives of two or three of the three fluids in system having a reaction - but none of those are in your system now so you just need to clean out the black residue from the system.

 

MoCool - "Can be mixed with most coolants that are monoethyleneglycol based." - perhaps the key word here is most.  Or the two different anti-freezes that you used did not mix well, another reason to remove as much residue in the coolant system as you can at each coolant change particularly if you do not know or remember what anti-freeze is in the system already or there is to be a change to the anti-freeze being used.

 

22 minutes ago, nta16 said:

so you just need to clean out the black residue from the system

 

I have checked the thermostat sensor, crystal clear, the thermostat wasn't sticky, no overheating, the gauges are working as they should be, no smell inside the engine bay.

I have replaced the expansion tank and the cap, so far absolutely nothing suspicious inside, everything is blue colour and no signs of black sludge on the walls of it.

For sure i am not a Chemist but i think by boiling the system push all that black ''tar'' higher (as the lathe and the bubbles of the boiling water go to the top) and stuck in the plastic tank as for example when we boiling the meat.

 

I will post some photos from the new reservoir soon, everything is clear.

Good.  Was you able to see inside (the top of) the radiator (does it have a cap ) if there was any black tar, or to syphon the coolant level down in the radiator to check, the top of the inside of the radiator at least, has clear innards.

 

Sorry, I misunderstood this as an issue you were still having rather than a report of what had happened.

 

13 hours ago, nta16 said:

Sorry, I misunderstood this as an issue you were still having rather than a report of what had happened.

 

No problem, i forgot to mention that this happened after the ''flushing process" of removing old coolant-adding distilled water-after few days remove etc. I have posted 2 photos from the results:

 

https://i.imgur.com/5DsAznt.jpg

 

https://i.imgur.com/dfnsge9.jpg

 

Then i added the Amsoil additive and maybe this reacted chemically with the remains of the old ''bad'' coolant and the result was that black sludge inside the plastic reservoir.

After i removed that expansion tank plus about 700ml that had inside i installed a new plus a new cap.I had it for a week now and everything looks fine.

I am not Chemist but i think that by boiling the remains of the old thick coolant were pushed to that expansion tank and stuck on his walls, i there were any remains would show-up inside the new reservoir after a week?

I hope not but if there is a change i will let you know.

Yes I remember those photos, whatever it was hopefully it is all gone now.

 

 

 

Yesterday noon

 

 

 

and a night photo with flash, no black sludge on the top of the plastic tank, i think i was lucky and the whole system didn't affected.