Coolant is black and sludgy

[Johnnyb]

Howdy everyone,

I decided to change my thermostat and when I went to drain the radiator I discovered that the coolant was black and somewhat sludgy. It doesn't look oily, it's more like goo. There's also no water in the oil nor did it seem to be losing any coolant or leaking anywhere.
I have a 95 5.0 block with an explorer serpentine and an aluminum intake manifold. I also have an aluminum radiator with an anode radiator cap.
I filled it up just a little over a year ago with a 50/50 mixture of antifreeze and water and haven't given it a thought since. Imagine my surprise when I went to drain it and saw what was coming out!
Anyone have any idea what would cause antifreeze to turn black like that?

THX,
JB

 

[1969]

Someone could have filled your engine with stop leak at some point. I’d flush really good a couple times and keep an eye on it.

 

[DirtDonk]

Did the coolant flowing past the filler cap look normal before you drained it? Or did it also look like the black goo?
It’s normal for some contaminants to settle to the bottom, and to have some of it come out when you drain. And some stop-leaks too, as 1969 mentions.
Or are you saying that every drop that you drained out looks this way?

If so, that might not be too good…

 

[Johnnyb]

Did the coolant flowing past the filler cap look normal before you drained it? Or did it also look like the black goo?
It’s normal for some contaminants to settle to the bottom, and to have some of it come out when you drain. And some stop-leaks too, as 1969 mentions.
Or are you saying that every drop that you drained out looks this way?

If so, that might not be too good…

It didn't look like antifreeze when I drained it. I never observed the coolant in the radiator while operating, just didn't seem to be a need.

 

[Broncobowsher]

How gone is the anode?
Rubber hoses rotting from the inside?

 

[Johnnyb]

How gone is the anode?
Rubber hoses rotting from the inside?

Anode was fuzzy and green, brand new hoses - silicone heater hoses.

 

[.94 OR]

When you get to flushing, remember to engage the heater core to get fresh fluid there too.

 

[LUBr LuvR]

Used this on a radiator/cooling system that a PO had neglected. Seems to do a pretty good job. Have to run the truck for several hours over a few days or up to a week - which can be challenging during cold weather, as there’s no antifreeze protection while treating

The coolant in that rig wasn’t bad, but the bottom of the radiator was full of sediment. Nothing came out the petcock when opened.

Has anyone used this? Interested in hearing other’s opinions and experience.

https://www.evapo-rust.com/thermocure-cooling-system-radiator-rust-remover/

 

[Johnnyb]

What worries me is that I flushed the block and everything else was brand new 1 year ago.
I'll keep my eye on it and let you guys know what happens.

-JB

 

[DirtDonk]

What type of antifreeze do you normally use?
Did you, or perhaps someone else, add any in that last year?
Also, why were you changing the thermostat in the first place? Did you feel it wasn’t working properly?
Could possibly be due to the sludge, of course, but curious what was going on.

 

[Johnnyb]

So here's a picture of the anode.

 

[Johnnyb]

What type of antifreeze do you normally use?
Did you, or perhaps someone else, add any in that last year?
Also, why were you changing the thermostat in the first place? Did you feel it wasn’t working properly?
Could possibly be due to the sludge, of course, but curious what was going on.

So I drove down to Prescott last week for an alignment and it was cold out. The truck ran at 140 the whole way. Normally it comes up to 180 pretty easy and stays there. I pretty much knew that thermostat wasn't working.
I typically use a 50/50 mix of store brand pure antifreeze and tap water. I can't honestly remember if this was red antifreeze or green antifreeze, but you sure can't tell right now. I did dip it with hydrometer and it tested to -50.

-John

 

[Johnnyb]

How gone is the anode?
Rubber hoses rotting from the inside?

I just posted a picture of the anode and the hoses look good on the inside.

 

[1969]

I wouldn’t be to concerned. Personally I’d flush it and keep driving it. Your engine is 30 years old, you never know if in the donor vehicle the radiator or something was leaking and someone filled it up with stop leak. It could have just loosened up and you are seeing it now.

 

[Johnnyb]

I wouldn’t be to concerned. Personally I’d flush it and keep driving it. Your engine is 30 years old, you never know if in the donor vehicle the radiator or something was leaking and someone filled it up with stop leak. It could have just loosened up and you are seeing it now.

That's the plan. I had the heads off and flushed the block right before installation.