Mustard in coolant?

[1 Lucky Texan]

I don't have any indications of a problem, but , when checking some fluid levels, I saw some mustard yellow substance deposited on the rad cap and on the inside surface of the filler neck. My GUESS is it may be the sealer that Subaru now includes in the cooling systems. Have any of you guys used the sealant stuff? Is it yellowish?

[Strakes]

Had the same mustard yellow stuff in my car. Gone since the last flush. Don't know what it is.Yes, I used the sealant stuff even though my VIN was after they fixed the HG issue. The Subaru sealant stuff was not yellow when I added it in. Maybe it discolors to yellow after a while.

[OB99W]

A yellowish "gunk" is usually formed by an oil/water emulsion (think mayonnaise). If there were a lot of it, I'd be concerned about head gaskets (but you'd likely have other symptoms). A small amount may just be due to anti-corrosives from the antifreeze. Since oil typically floats on water, and the radiator neck and cap are the high points of the cooling system when the car is level, what you see at the neck area is probably not indicative of the rest of the cooling system.

 

Also, on cars with an auto trans, the trans fluid cooler (which is located in the radiator) can sometimes develop a leak, and trans fluid can get into the coolant. However, I'd expect that emulsion to be more redish.

 

As precautions, besides keeping tabs on the coolant level, take a close look at the engine oil dipstick (and trans one, if auto) and make sure you don't see any similar emulsion.

 

--OB99W

[1 Lucky Texan]

A yellowish "gunk" is usually formed by an oil/water emulsion (think mayonnaise). If there were a lot of it, I'd be concerned about head gaskets (but you'd likely have other symptoms). A small amount may just be due to anti-corrosives from the antifreeze. Since oil typically floats on water, and the radiator neck and cap are the high points of the cooling system when the car is level, what you see at the neck area is probably not indicative of the rest of the cooling system.

 

Also, on cars with an auto trans, the trans fluid cooler (which is located in the radiator) can sometimes develop a leak, and trans fluid can get into the coolant. However, I'd expect that emulsion to be more redish.

 

As precautions, besides keeping tabs on the coolant level, take a close look at the engine oil dipstick (and trans one, if auto) and make sure you don't see any similar emulsion.

 

--OB99W

 

Yeah, I've seen the chocolate mousse before - unfortunately too many times - on other vehicles I've owned. Honestly, if I could think of how/why its in the cooling system, I'd think it was that yellow 'QC' paint that they hit different areas with. I'm guessing it is part of the QC to inspect/mark certain bolts, etc. with paint. I dunno. It just kinda offends my sense of order to see anything not a liquid in my radiator.

[JohnnyB]

1 Lucky Texan,

 

When was the last time you changed/flushed your coolant? I had what sounds like the same stuff on my rad cap and tube last year when I was overdue for a coolant change. Just assumed it was scale, never used the additive and still have the original HG's and no signs of any problems.

[1 Lucky Texan]

1 Lucky Texan,

 

When was the last time you changed/flushed your coolant? I had what sounds like the same stuff on my rad cap and tube last year when I was overdue for a coolant change. Just assumed it was scale, never used the additive and still have the original HG's and no signs of any problems.

 

I shoulda' been more clear - this is in my '06 WRX wagon. Brand new. Seems unlikely to need a coolant flush. maybe the dealership can tell me what it is?

[JohnnyB]

Ahh, I see, well if the dealership tells you anything, let us know.