Hello, My antifreeze is turning dark brown after running the car for 20 min. Car has original motor with only 40,000 miles but it did sit for 15 years. I have flushed the complete system over 10 times till it runs clear and have used rad flush solutions and it still turns dark brown after 20 minutes of running. It does not appear to be oil, car runs and idles good, cooling system will build up good pressure and car runs cool and the oil pressure by the factory gauge is very good and the oil dip stick is clean. I also pulled the plugs and they seem fine. Possible head gasket ??

 

Flush again and drain COMPLETELY as in remove the plugs in each side of the block at the oil pan rails. Use distilled water mixed with antifreeze when you refill.

 

It may be that the system will require more aggressive cleaning, although more harsh caustics can potentially affect the gaskets and other soft materials in contact with the coolant.

It could also be that the complete draining (down to the core plugs) as N-E 87TA suggested could be the only solution short of disassembly and hot-tank cleaning. I'm betting you would prefer routine draining/refilling instead of that.

 

Thanks for the replies. If it just needs more flushing or a drain down that would be a good thing, not looking forward to a head gasket repair I am going to do a pressure test and check for exhaust gases in the coolant.

 

What those guys said, but instead of draining, filling, running, draining, over and over and over....that's an f'n waste of time...and not all that effective b/c you're only flushing about 1/2 of the coolant in the system and you're definitely not getting the **** out of the bottom of the block doing it that way.

Here is the fast/easy/effective way to do it.

Drain the radiator, pull both block drains (one is the knock sensor). Remove the "return" heater core hose, where it connects to the water pump. Stick a garden hose into that heater core hose and turn it on....run it until the block drains run clear. That reverse flushes your:
Heater core hoses
Heater core
Intake
Heads and...
block...
....until water flowing out is clear. Blow low pressure air (using your mouth, works) into the same heater core hose that you had the garden hose hooked to, to push the slug of raw water out of the heater core, let that drain out the block drains too. That part is done.

Disconnect your upper rad hose from the t-stat housing, stick your garden hose in that, turn it on full blast. That'll reverse flush your
upper and lower rad hoses,
the radiator, and
water pump.
....and it'll drain out the block drains again. Do that until the water runs clear out of the block drains, again. Then drain remaining caught in the lower rad and lower rad hose, out the radiator drain. Now, it's ALL flushed.

Hook everything back up, fill w/50/50 premix so that you avoid water issues and/or mix ratio issues. Easy button. Thorough. Proper.

Change fluid as per what ever coolant you chose's, recommendation.. No one does that last part, which is why you see threads about sh!tty looking coolant, bad heater cores and cars running hot.

 

Great post. I guess im pulling the block drains are they easy to get to with the motor in the car ?

 

Yeah, relatively easy to get to but if they've never been removed in 41 yrs don't snap them. If they won't move soak them or heat them. I've pulled them in the past and actually had to knock out the debris w a tool to get them to drain well. It's the low point in the block and all the crap accumulates there. It's totally the best way to flush things.

 

Once you get the plugs out of course.

GOTTA pull those. If you don't, the better part of a gallon of coolant, remains in each side of the block, by only draining it via the water pump (the next lowest possible drain point), which is the best you can do by only pulling the lower rad hose.

The driver's side one is yerbasic steel pipe plug. The pass side has the knock sensor in it. See, those Chevy engineers were so forward-thinking, that in 1955 they anticipated the introduction of EFI, butt to keep those morons at Frod and Xler from recognizing what they were up to, they cleverly disguised the KS location as a drain plug. Pure genius.

The KS usually comes out without too much of a fight. The plug on the other side however, being steel, now has 40-odd years of rust welding it into place, and usually makes you EARN it by the time you get it beaten into submission. Best to use a 9/16" impact socket and the longest breaker bar you can fit. It'll just laugh at some weenie 12-point socket and a 3/8" ratchet. Replace it with a brass one. It's ¼" pipe; you can get a brass plug that size anywhere that sells plumbing goodies.

 

I finally pulled my block drain this year and indeed the sediment had to be picked out before anything flowed out. Somehow splashed all over my face because I'm graceful like that, fortunately I was wearing goggles so it wasn't a big deal.

I replaced the drain with a speed drain from summit:

https://www.summitracing.com/parts/sum-380668

 

^Those are handy/quick/easy....IF you've already gotten the engine flushed out good and then maintain it. Which you probably did, but for those who are embarking on cooling system "restoration", they want as big a hole in the block as they can have to help all the chunks, scale, sediment and small animals flush out.

 

Very informative !