Spartan 45

2005 with z51 - Seeing a light brown residue like tooth paste in my coolant resovior. Coolant is 3 months old ( Dexcool) Oil is ok with no anomalies. Normal operating temp is 197. Any ideas ?
I got a new tank, but considered doing a flush and fill first.

4SUMERZ

How old is the coolant in the car? Have you changed the coolant in the past?
The coolant age and temperatures may leave a slight residue in the fill reservoir, which is easily removed with a high pressure washer if you remove the tank from the car. You can also use Lime away products as well to disolve the residue.
I changed my coolant at approx 30K miles, and the reservoir had a slight brown residue on the interior. I did have a water pump seal leak, which dropped the coolant level some, so I attributed that to the residue because of the possible higher running temp at that time.
I cleaned the reservoir, added new coolant and that residue has never come back. I now have 85K miles, and due for another flushing and coolant change.

That's all I have to offer.

CorvetteSparky

From my experience (which wasn't a good one) that's an indication of oil in the fluid. This means a bad head or intake manifold gasket is letting a small amount of oil leak into the engine coolant.

Spartan 45

LV2TOUR,
Thanks for the input. The coolant is since May of this year. I dont see normal operating temperature specified in the manual. This is my 5th corvette and have never experienced it before. Nothing else is out of the ordinary with the car. I wondered if the oil cooler (z-51) option had some internal leak, but it is clearly not oil.

Spartan 45

I wonder why there would be no indication of water in the oil - less pressure on that system? No smoke in the exhaust either.

Arkyvette

This sounds like the stop leak pellets GM liked to put in northstar engines from the factory. Some dealers drop them in everything with a mild leak or complaints of coolant smell. They can leave a brown residue.

RICH 28

Yep, stop leak.

ruxvette

Damn...I learn something new every day!

Spartan 45

Interesting ! i sold my 05 vert for CTSV, kids got their license and drive now, just bought another 05 vert w z-51. I SEE IN THE CARFAX THE RADIATOR WAS REPLACED AT 64,000 MILES. Suspect the previous owner used stop leak before having to replace the radiator.

If it is stop leak...Can it be flushed out before I put the new resivoir on , or is it just all over the inside of the engine coolant internals forever ?

Spartan 45

Looks like Texas may have solved the mystery for me. Now the question remains as to what is the best course of action to clear it out...

RICH 28

I had a coolant leak on one of my other cars and used Bar's stop leak until I properly fixed the leak. I had to replace the intake manifold gasket. I drained and filled the system at least 5 times and still could not get all of that Bar's stop leak brown crap out.

It doesn't really hurt anything, just looks ugly.

Spartan 45

Thanks RICH 28 LOTS OF EXPERIENCED VETERAN OWNERS OUT THERE. Have a good weekend. May you have all of the "close up" Avatars you desire" ....I saw a response to another post a few minutes ago, LOL.

HammerheadTed

Sounds like good news for you, because I would have said with confidence that it was oil. If you are loosing any coolant, make sure there is mo moisture on the oil dip stick. Stop leak in the fluid will eventually stick somewhere, probably harmlessly. You can drain the fluid, scoop all the floating brown stuff off and put it back in.

owc6

Yep, but they do work quite well.

Spartan 45

I spend my summers vacationing in the Islands.....Usually Broomes and Solomons, LOL. Hello neighbor. I am right around the corner.

owc6

"the Islands".

Howdy!

AORoads

Me. too. I thought Stop Leak was long gone. Good to know it doesn't clog things up.

It is kind of odd to read that the rad was replaced at 64K miles tho, which may mean it went bad earlier than that. What year was the rad replaced---my guess is relatively recent?

Spartan 45

Radiator was replaced in 2015. I have a new tank for it. I have been used to seeing a peach/ pink color on past vehicles, not caramel.

Mad*Max

Does anybody know why some cars exhibit this brown residue/foam on the walls of the coolant reservoir and some don't? It is happening on my wife's 2012 Sonic but haven't seen this on my older GM cars. Also, does anybody know if it harmful to leave the brown residue in their or is it a must to have the system flushed and refilled? The car is not losing oil, there is no smoke in the exhaust and my untrained eye does not see any coolant on the dipstick.

Redvette2

Have a 2007 LS2 auto with 63K miles. After reading this post I had to go and check my car. The inside of the "surge tank" was clean fortunately and the fluid had a clear light pinkish red color. Slight amount of white residue around the inside of the cap. I am the second owner but know according to CARFAX that the fluid was dealer changed in January of 2014 (16K miles since). Seems like any Stop Leak residue coating the internal parts would likely also reduce the heat transfer and should be avoided no mater what.