Coolant getting dark

[Falcon_LS]

The cooling system was neglected by the previous owner in my Grand Marquis, and took a good couple of flushes before the system looked clean.

A while back, one of the coolant gaskets on the intake manifold failed (driver's side, near the brake booster) and I have to add about a liter or so of distilled water every 3 weeks or so. So I do not upset to 50:50 ratio, I add Motorcraft G-05 instead every third or forth time and keep an eye on the ratio with a Prestone coolant concentration tool I bought. It's a very minor leak, and does no harm. I haven't corrected the problem, because I decided it will work to my advantage - help clean up the cooling system very slowly.

When I checked the coolant level this morning, it was about 500 ml low and instead of adding distilled water, I used an extractor to remove all the coolant in the reservoir. I added 2.7 liters of distilled water to compensate.

The coolant I extracted looks rather mucky and brown in the container I used. When you take a small sample, it looks lighter. But otherwise, it looks very dark...almost a very dark orange-brown color. Here's a 200 ml sample (apologies about the lighting):

I was wondering what would cause the coolant to go dark like this. Initially, the coolant was a very nice, bright yellow color and I would have assumed it would stay clean with all the fresh stuff going in.

 

[Eddie]

Did you used distilled water or tap water? Tap water may contain minerals which may have caused the darkening.

 

[Boomer]

I'd go with some rust in the system. You might benefir by flushing the system with an oxalic acid cleaner followed by a good flush to get it out of the system. Then refill with new coolant and distilled water. If the leak is minor, add a small amount of a leak stopping chemical. You should be good to go.

 

[rclint]

If you have a small leak I have seen this cause problems with the cooling system such as you are having. I'm not sure if air is getting in the system causing the oxidation etc... but for sure the leak would be the first thing I would focus on. I have used Bars gold tablets stop leak with outstanding success in the past, you can also get these tablets at a GM dealer (they invented them for problems they had) still the tablets are by far the best stop leak i have found as of yet.

After you get the leak fixed focus on getting that system flushed, cleaned, and back into proper service. This will take many flushes with distilled water, and cleaners.. I have even used dishwashing soap/powder) cascade etc) to flush out a system.. I'm sure I will get chas-tised here, but it worked, and the system was also on it's last leg, my other option was to replace the radiator.

 

[bullwinkle]

I would check for a combustion leak with a kit-that's exactly what the G-05 in the Ford 6.0 diesel van looked like when I had head gasket trouble-although there was some sludge mixed in as well.

 

[Falcon_LS]

Originally Posted By: Eddie
Did you used distilled water or tap water? Tap water may contain minerals which may have caused the darkening.


Distilled water. Never use tap water in my cooling systems.

Originally Posted By: Boomer
I'd go with some rust in the system. You might benefir by flushing the system with an oxalic acid cleaner followed by a good flush to get it out of the system. Then refill with new coolant and distilled water. If the leak is minor, add a small amount of a leak stopping chemical. You should be good to go.


Considering the previous owner never replaced the coolant, and 10 year old (conventional green) coolant was still circulating in the system (with tap water top offs and the occasional Dexcool when the water pump was replaced), I suppose that very well might be the case.

The leak is minor, and I only require a top off of a pint every 3 weeks.

For the time being, I think I'll just use my extractor and keep replacing the coolant with distilled water slowly until it is clean and then replace the gasket instead of using a stop leak product. I'll follow that up with flushing it all out and running a dish washing tablet with fresh distilled water for about 1,000 km (625 miles), before flushing out the system again:

Originally Posted By: rclint
If you have a small leak I have seen this cause problems with the cooling system such as you are having. I'm not sure if air is getting in the system causing the oxidation etc... but for sure the leak would be the first thing I would focus on. I have used Bars gold tablets stop leak with outstanding success in the past, you can also get these tablets at a GM dealer (they invented them for problems they had) still the tablets are by far the best stop leak i have found as of yet.

After you get the leak fixed focus on getting that system flushed, cleaned, and back into proper service. This will take many flushes with distilled water, and cleaners.. I have even used dishwashing soap/powder) cascade etc) to flush out a system.. I'm sure I will get chas-tised here, but it worked, and the system was also on it's last leg, my other option was to replace the radiator.

Originally Posted By: bullwinkle
I would check for a combustion leak with a kit-that's exactly what the G-05 in the Ford 6.0 diesel van looked like when I had head gasket trouble-although there was some sludge mixed in as well.


There's no sludge in the system, and the oil looks very clean. But that is scary, so I will get it done for peace of mind!

Thanks very much for all the input!

 

[Falcon_LS]

An update. I left the bottle over night, and when I checked it in the morning, the coolant was a brighter orange color.

There was brownish-orange residue collected at the bottom of the bottle. Shook the bottle, and the residue mixed with the coolant and darkened it again.

 

[Falcon_LS]

Some pictures I have taken to illustrate my previous post. This is what the bottom of the bottle looks like after it has been allowed to sit for a while:

The bottom of the bottle isn't level, it expanded after it was left in the trunk for a few days before I poured the coolant in. Here you can clearly notice just how much material has collected at the very bottom:

Another closeup:

After shaking the bottle, whatever was collected at the bottom mixes back in with the fluid:

If you pay close attention, the coolant has gotten darker under the same lighting conditions compared to the previous pictures, where the stuff sat at the bottom: