Black contamination in coolant

[Alfajay]

The coolant in my 1600 Giulia spider has turned very black and has an oily feel. My first guess was that this is the result of oil leaking into the cooling system, though I am wondering if instead this could be caused by a combustion leak. The odd thing is that no coolant has appeared in the oil – the dipstick shows no signs of "milkshake". So, one question is how to test for the source of the leak (i.e., oil vs. combustion) before disassembling the engine. Is this what a "leakdown test" is for?

My next question is: where is the most likely point for oil/combustion to leak into coolant? The head gasket seems like the obvious place to begin, but where specifically? I don't want to take everything apart, install a new head gasket and O rings, and still have the leak.

Once I get the leak repaired, how can I clean the oily residue out of the block coolant passages? The radiator and head I can easily have boiled out while things are disassembled. But should I also pull the block so that its passages can be boiled out too?

The engine is a 101 1600, but has 80mm (1750) pistons, a 1750 head gasket and a 105 1600 head – do any of those modifications make a difference? The engine runs great, has good oil pressure, good compression, etc.

[andy303]

When the engine in my car blew a head gasket it was from combustion leaks visible in the gasket between cylinders 1 & 2 and 2 & 3. The escape of the combustion gas greatly pressurized the cooling system, but never discolored the coolant.

I have edited the post with pics of the blown head gasket, top and bottom. Note badly burned out edge adjacent to the coolant passages.

[Gordon Raymond]

Some of the new coolants react differently to oil, fuel, and combustion chamber gas leaks than older versions. Those that are colorless, come to mind. Is the coolant opaque, or can you see through it? Some iron oxides will leave a black material in suspension, but it will settle out. As for the oily, grassy feel, most antifreeze also contains a water pump lubricant and anti-oxidants. Both feel slippery. When was the last time you changed coolant? Most are good for 2 years, but get cloudy after that.
Now, oil leaks almost always come from the oil passages between the head and block. 2L use roll pins, but 1600's benefit from John Norman's brass fittings that fit the block, and allow the use of a flat "o" ring around them. Head gasket failure, where the gasket becomes porous between an oil gallery and water passage, is also a possibility. Only use the best head gasket you can find, unless you enjoy tear downs. As Andy mentioned, often a blown head gasket as he describes, will seriously pressurize the cooling system, sometimes enough to cause overheating (pump cavitation) and / or blown hoses! This is always a mess, and comes on pretty quickly. However, some 1600 heads suffer a often seen failure. A crack appears between the root of a plug thread, and extends to the exhaust valve seat. This crack is sometimes partial, just from the plug hole toward the exhaust seat, or can extend all the way. This crack can, but not always does, penetrate to the coolant passages in the head. The crack starts on the surface, and grows deeper over heating / cooling cycles. If it penetrates slightly, you may loose coolant as the increased pressure blows it out the overflow. As the engine cools, some coolant ends up in the combustion chamber, where again, over time, it will show as pits in that chamber. The good news is that this can be repaired, and EVEN PREVENTED (perhaps)!
With the UNCRACKED head off, I use a flap wheel to cut back the lower threads in the plug hole, so there is no sharp thread edge to act as a stress riser. Some 1600 heads are not threaded all the way to the chamber edge (thats GOOD) as this was already done. Next, check your Reinz head gasket. Newest ones block water passages between the stud holes. Older ones do not. We used to drill tap and thread aluminum rod into these holes to block them, but the new head gasket does that job for you. This prevents hot and cold spots within the water jacket that promotes crack development.
If the head is cracked, it can be repaired by a shop that specializes in the repair of Alfa and Ferrari heads. The weld requires the removal of the valve seat and a weld with full penetration. The head must be heated quite hot before welding, and cooled slowly to minimize stresses. The seat recess is recut from the guide bore hole, and the plug hole redrilled, tapped and relieved as mentioned above. The chamber is reprofiled, the head hydraulically pressed flat, and a minimal clean up mill cut performed. Done correctly, the head will not crack there again. This is neither a cheap nor terribly expensive repair for a rare head, or one that has had expensive performance modification.
This is a long discussion of causes of black coolant Jay, but I hope it is helpful.

[Alfajay]

Gordon:

I did a little "explatory surgery" this afternoon, and what I found wasn't as severe as I had expected. So now I'm mystified as to what - if anything - to do.

I know that antifreeze has an oily feel, even when new. But, it doesn't turn your finger black when you run it around the inside of your radiator neck (see first photo below). When I noticed that, I figured that my coolant would be black throughout, and look like old motor oil.

But, when I drained the coolant, I was pleasantly surprised to see that it came out looking about the same color as when it went in a few years ago (see second photo below). Sure, it is about due for a change. But, it doesn't appear to be completely oil contaminated.

I also pulled off my upper hose, to see how oily that was. The answer is that its inside surface has some oil residue, but it is not as heavy as in the filler neck. I guess that since oil floats in water, all the accumulation that I have is concentrated at the top of the radiator.

Another symptom is that the oil degraded whatever adhesive holds the neoprene gasket to the radiator cap (see third photo below). I guess I can: a) glue it back on, b) just set the gasket down in the neck before installing the cap, or c) get a new cap.

Regarding headgaskets - I did use a Reinz gasket when I built the engine. And, retorqued the head every 500 miles. When I noticed the oil build-up in the coolant, I checked the head stud torque again - none seemed loose.

So again, what would you advise that I do? From what I saw today, I am inclined to just change the coolant, add a little Alumaseal, and continue to monitor it.

[Gubi]

You've never used Redline Water Wetter have you? That caused some black oily build up in my cooling system.

Doesn't look bad at all, really.

[Alfajay]

Gubi:

Nope, no Water Wetter. Can't blame that!

[Tifosi]

Quote:

Originally Posted by Gubi Redline Water Wetter.... oily build up in my cooling system

[Gordon Raymond]

Just curious, I checked all my vintage engines yesterday. They all had "some" oil scum in the top of the radiators. The Ferrari scum was blacker than the Alfa, yet both had coolant changes within the last year. The crud in the bottom of the Ferrari expansion tank (brass tank) was rust colored, the bottom of the radiator clean and clear. The Alfa (GTA) had oil scum, but greyish. No expansion tank, but the bottom of the radiator was again, clean and clear. The Ferrari has dry liners, the Alfa, obviously, wet. They both have aluminum blocks and copper radiators. The Ferrari has some STEEL connecting tubes in the system, BUT HERE WE GO... The inside of all the rubber hoses I touched in both engines left me with BLACK RESIDUE on my finger!! Now, I use Prestone in all my multi Alloy engines, mixed 50 /50 with distilled water. The GTA engine, on the track, ran distilled water, and "Bars-Leak" only. Now (just this year after 44 years) I switched it to Prestone, and am watching for leaks THROUGH the sand cast head. None as yet!
I believe the BLACK to be oxidation of the inside of your hoses. This is JUST A GUESS. Flush your system with regular water. NO AGGRESSIVE cleaners! Fill with 50 /50 Perstone and distilled water. Add one little plastic jug 'o Bars-Leak if you wish. Watch it for a year. Note coolant loss, or ANY greenish deposits on the spark plug inside center porcelain insulator. I think, the black is hose oxide. No big deal. You should be fine.

[Alfajay]

Quote:

Originally Posted by Gordon Raymond I believe the BLACK to be oxidation of the inside of your hoses. This is JUST A GUESS. Flush your system with regular water. NO AGGRESSIVE cleaners! Fill with 50 /50 Prestone and distilled water. Add one little plastic jug 'o Bars-Leak if you wish. Watch it for a year....I think, the black is hose oxide. No big deal. You should be fine.

[Gordon Raymond]

With Alfa's, Jay, that is always the best plan! I was contacted by a potential oil pump customer, that felt he needed a new pump for his 2L. After a lot of discussion about when the pressure dropped, his only (!) problem turned out to be a faulty water temperature sending unit, combined with a bad thermostat! Thermostat stuck only a little open when hot. (Then it got hotter!) Meanwhile the sending unit said "Everything is FINE" when it was actually VERY HOT! Ergo... low and dropping oil pressure. He was amazed that a new thermostat and water temperature sending unit could "fix" his oil pump!

[101/105guy]

Jay....
you just need to drive that Spider to Cars & Coffee more often !! ;^)

[Alfajay]

Quote:

Originally Posted by 101/105guy Jay.... you just need to drive that Spider to Cars & Coffee more often !! ;^)

[Gordon Raymond]

I prefer to look at it another way. Jay has USED antifreeze, thus avoiding the destruction caused in many warm areas of the U.S. where owners use plain tap water, and the electrolysis then eats up EVERYTHING! YOU SAVED IT JAY! Good job!