Soot in Coolant Overflow Canister

[John Dickson]

This past year I noticed that my port coolant overflow canister is turning brown inside and I am slowly losing coolant. It would appear that I may be getting soot in my coolant? When I remove my exchanger cap the coolant is at the top.
Any suggestions on where to start looking?

Thanks,
John

[SeaEric]

This is just a WAG - head gasket.

[DCMY #92]

What engines?

[Top Hatt Craig]

A combustion gas leak check is in order, Google 'engine block check' for combustion leak detectors that will confirm combustion gases are present in your coolant, hopefully from the fore-mentioned head gasket, and not from a cracked head.... or block.

To use, lower coolant level about three inches to prevent coolant from being drawn into the detector, then with filler cap removed, warm engine to operating temp (thermostat open) then add detector solution to detector and hold the cone-shaped rubber adaptor in place of your coolant cap and squeeze to bulb several times to draw gases through the detector solution.

If after a few tests no change in color is found, resume normal use of engine as there is not enough indication it needs to come apart.

If the detector solution turns color, engine disassembly to find the exact cause is next.

The head gasket is by far the most likely cause, but when I was just getting started working on cars I did a head gasket on an early VW diesel. The car returned with the same symptom it had before. I pulled the head back off and the very gruff old salt German I was working for looked it over then said "bring the torch".
He proceeded to heat the head, and then the block where a until then invisible crack opened up between a head-bolt hole and a cylinder bore.

Best wishes, Craig

[dottieshusband]

If it's a 71 series, there is no head gasket per se. Each cylinder has an individual sealing ring. Soot in the coolant is something I know a little about. There could be several causes. Your exhaust manifold would be a possible source, as exhaust gasses, and engine cool and are in close proximity. A cracked dry liner could also introduce exhaust gas to the coolant. A liner not installed to the proper height would allow exhaust gas by the sealing ring, but there is a rubber ring sealing the water ports, or a cracked head. Two clues to look for would be excess pressure in the coolant tank, and cylinder and crankcase pressures. The test kit mentioned before are not as sensitive on a Diesel engine. It works, but the color change is not as dramatic, so work the kit several times. If the compressions are good, crankcase and coolant tank pressure good. I'd clean the heat exchanger, flush the system, replace the zincs, put new pink stuff in, and run it awhile before tearing it apart.

[dottieshusband]

There are also a couple of other avenues for soot.. cracked or mis-seated injector tube or water nozzles could also intorduce soot, but as Billy Bob Thornton said in Slingblade, always check the simple things first!

[Haylands]

How old is the coolant? Anti-freeze and summer coolant additive have a corrosion inhibitor, as it ages it looses the will to live and the coolant will start to rust the inside of the engine and turn the water brown, this then leads to small leaks that immediately dry before you see a drip, you could pressure test the system when cold to see if you have any external leaks before pulling the engine apart...

[Dan Mapes]

Could be a leaky injector tube? You could pull the inspection plates and look for a clean piston crown, or a drip when the engine is warm.

[saltshaker]

How old is the coolant? Anti-freeze and summer coolant additive have a corrosion inhibitor, as it ages it looses the will to live and the coolant will start to rust the inside of the engine and turn the water brown, this then leads to small leaks that immediately dry before you see a drip, you could pressure test the system when cold to see if you have any external leaks before pulling the engine apart...
This is what I was thinking. If the coolant is old or if you mixed incompatible coolants, the coolant will turn brown. The loss of coolant is something to be concerned with. Are you sure you're loosing coolant? I thought I had an issue but after topping off the tank a bit I later found the lost coolant returned and now the level in the expansion tank was high. I learned from Dave/captddis that if you fill the heat exchanger to above 2" from the top, the coolant will get pushed out. Once I set the proper level, I never saw what I thought was a loss.

[GJH]

A picture of the stuff might help. I had the coolant in the overflow tank of my genset turn brown, which was caused by the heat exchanger gone bad, introducing sea water into it. Was losing coolant as well. Caught it early, fortunately.