Black coolant in system after engine change.

[renniweht]

My dads G6 GTP broke a valve spring about 4 months ago and I just got around to getting a new engine in, well a used engine with 35K on it. Got it all in and running then all this black coolant starting showing up in the reservoir and it smells horrid. Flushed the system out and ran a cleaner with water through it for about a week, drained it tonight and same deal black smelly water. The engine is running good and isnt pressurizing the cooling system although im starting to think the engine is bad because of this coolant issue. I have attached a pic. Any thoughts?

[TGP37]

My dads G6 GTP broke a valve spring about 4 months ago and I just got around to getting a new engine in, well a used engine with 35K on it. Got it all in and running then all this black coolant starting showing up in the reservoir and it smells horrid. Flushed the system out and ran a cleaner with water through it for about a week, drained it tonight and same deal black smelly water. The engine is running good and isnt pressurizing the cooling system although im starting to think the engine is bad because of this coolant issue. I have attached a pic. Any thoughts?

Could be rust and aluminum oxide. Sometimes the coolant jacket walls rust a little with the coolant drained or partially drained.

My coolant was tinted dark brown/black from rust when I had the block torn open down to the heads for a few weeks.

Got a flush kit and back flushed while running, took a few minutes to clear it all out. I suppose it is possible your replacement block might have sat for some time and might have built up rust sludge or other debris in the coolant system.

Aluminum Oxide is pretty dark, you may have that contamination instead of rust or a combo of.


Or.......Dexcool and Green coolant were mixed and sat for some time in the block together. Could also be some form of bars leak once used before you got the engine.

I've heard hard tap water used often can contaminate a coolant system.


You may just need to keep cleaning the coolant system. Use a good quality cleaner and take her out for a good hard drive (if all is well). Flush and repeat.

[pocket-rocket]

I would go with a really really good flushing as well. Oil and coolant mixing makes a chocolate pudding brown color. I've never seen black in the coolant like that. That would almost lead me to think combustion contamination, but you've already mentioned the cooling system isn't pressurizing...

Just to be safe, you could run down to your local Autozone (not sure if Advance has this item, but I can't stand Autozone and it's my last resort) and rent a "block test kit". You have to buy the liquid for it. It's a cylinder that you put the liquid in and place it at the coolant fill neck and use a squeeze bulb to draw air from the cooling system through the liquid. If combustion byproducts are found in that air from head gaskets, cracked block or heads or whatever the liquid will go from blue to yellow.

It's cheap assurance, in my mind. Hopefully it's just built up junk in the block like TGP said.

[TGP37]

I didn't catch the no pressurization part.....in light of that, pocket rockets suggestion to test the coolant is a good idea. When I first read it I thought it said pressure was good....oops, lol

Do you have excessive white smoke from tail pipe when all warmed up? Dripping water from tail pipe?

Is your oil cap getting a mayo like film underneath?

Did you bolt the heads on yourself or was the motor sold complete?

Is your oil level dropping while coolant level rising? Visa-Versa?

With the coolant cold, leave rad open and top off. Start car and see if you get bubbles in the coolant after a small rev. You have a minute or two before the heat starts pushing coolant out.



The problem with a used motor is you really don't know what was done to it. Dexcool and green coolant may have been mixed which is bad, it may have sat and was allowed to rust internally, may have had bars leak product(s) used.

Fortunately, this is a fixable problem if not allowed to persist. More then likey you got a leak or contamination.

[pocket-rocket]

When he said the cooling system wasn't pressurizing I took that as it wasn't building more pressure than its supposed to, like it could if a head gasket were blown.

I made my suggestion on the block tester just to help settle his mind some as far as blown gaskets goes. It seems unlikely with only 35k miles on the new engine.

Without being there I would think it's just built up crap in the system, but I've never seen coolant go black like that before, but with carbon being black, that's why I drew my thoughts to try a block tester just to rule spent hydrocarbons out.

[TGP37]

When he said the cooling system wasn't pressurizing I took that as it wasn't building more pressure than its supposed to, like it could if a head gasket were blown.

I made my suggestion on the block tester just to help settle his mind some as far as blown gaskets goes. It seems unlikely with only 35k miles on the new engine.

Without being there I would think it's just built up crap in the system, but I've never seen coolant go black like that before, but with carbon being black, that's why I drew my thoughts to try a block tester just to rule spent hydrocarbons out.

I do agree with your suggestions and understand why.

EDIT: Hard to say what it is but this is one idea....

If the coolant is highly acidic, from deposits in the coolant jackets, a galvanic action occurs when aluminum is exposed to acid. This forms aluminum oxide.

Previous coolant could have been left to puddle in the jackets over time and that will turn the coolant very acidic, especially if condensed from evaporation.

You can test for this issue by testing the voltage of the coolant against the engine ground. A charge is created when this type of thing happens. Not a lot but more then background variance.

Seems crazy but it was the first impression I got when I saw the coolants dark storm grey hue.

I was told the corrosive protection in the coolant can be reduced greatly if orange and green coolant are mixed.

This is aluminum oxide, notice the color.