Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Corrosion in my cooling system

I have a 2003 Chevy Impala with the 3.4L engine and I can’t seem to get rid of yuck in the cooling system.
I have flushed the system several times and then added fresh coolant, and each time I do the cooling system is brown in no time at all. When I do the flushes, I run the flush for the recommended time, then I flush with water 5 or 6 times to clean it out. Rather than bore everyone with my thoughts on what is causing this, i am just wondering what the most likely cause/solution is as I am stumped…

The first thing I’m going to ask is, how long was the Dexcool left in there? And have there been any coolant leaks in the past?


Dexcool wasn’t left in there very long at all, in fact the flushes have occurred fairly close together because of this problem. Yes there was a minor coolant leak, didn’t lose much as it was in a by-pass hose.

Radiators House An Integral Transmission Fluid Cooler. Should That Cooler Leak Inside The Radiator Then Transmission Fluid Can Mix With The Coolant, Turning It Brown.

Also, a faulty gasket (head, intake) can allow fluids to cross contaminate other fluids (coolant, oil).

More diagnosis might be justified. How is the level and purity of other fluids, engine oil and transmission ?


I mean, how long was the Dexcool in the cooling system prior to having this problem?


I would stop using chemical flushes, if you don’t get them completely out, they cause problems, sometime even when you do get them all out.

Are you opening the block drain as well.? You have to open both the block and the radiator drains.

Original Dexcool was removed back in 2005-2006. Couldn’t locate block drain which is one reason I ran water through so many times.

Then remove both radiator hoses and flush that way. You may have to remove the thermostat was well so it might be a good time to just replace it. It would be best to locate that block drain though.

I just need to make sure that that is the actual problem. The Mocha water just seems to be too much even after the flush…

I suspect you aren’t flushing every nook and cranny when you do the flush. Try this: Drain and fill it with a fresh 50/50 mix, drive it a week, then drain it all out and repeat, filling with a fresh 50/50 mix again. Be sure to bleed the cooling system as described in the shop manual. And be sure to drive long enough to bring the coolant temp to normal for a warm-ed up engine and to turn the heater on full hot as much as possible while you drive. You may have to do this several more times over the course of a couple months. If all that doesn’t produce a clear coolant, then there may be a path from either the xmission fluid or the oil or exhaust gasses into the coolant. A good mechanic can confirm/disprove with various test all three.

throw in some peak global and call it a day.

I’ve not had any issues with other fluids (at least until now.), which is why I have ignored the GM faulty intake gasket issue. The car has always been good on oil use so I haven’t checked for that. Unless it’s a very small leak. Tranny fluid hasn’t been an issue as far as I can tell. guess I will do a system pressure check, verify the tranny fluid again, and then pull my hair out…

Make sure that you are not leaking transmission fluid into the radiator. Check your transmission fluid leve when the car is warmed up. It should be nearly full. If you can’t see fluid on the dip stick, you should investigate further.

My granddaughter had a 95 Skylark and her coolant reservoir had what looked like dirty oil in it. My mechanic who works on a lot of older GM cars, looked at it and said “I don’t know what it is, but they all do that and it doesn’t seem to hurt anything” .
As long as you don’t find milky looking oil on your engine or transmission dipstick I wouldn’t worry about it.