Oil in the coolant

[Nelson]

Got my brakes installed and bled so I thought we might take it out for a test drive. I let it idle for about ten minutes and the temp stabilized at about 160 degrees. I shut it down and checked the coolant just for the heck of it. It looked more like a chocolate milk shake. So I ran about ten gallons of water through it but probably need to run even more as it’s still not clear. I’m pretty certain there is oil in the coolant but my first shot at it will be to by pass the automatic transmission cooler in the radiator. If this doesn’t fix it where would you look next? 

[Mark L]

The transmission cooler is a good bet, but I would think the coolant would be more of a pink color than chocolate, unless your transmission fluid is really old and needs to be changed. The only other alternative I can think of is a blown cylinder head gasket.

Edited February 22 by Mark L

[Gunslinger]

If there was a blown head gasket or cracked cylinder head there should be coolant in the crankcase oil.  Smell the dipstick and see if it smells like anti-freeze…the exhaust would have a similar smell.  If that’s the case…don’t drive the car…ethylene glycol and engine bearings do not get along.

[Nelson]

There is no indication of water in the crankcase and no steam out the tail pipe. No sign of water in the trans either. I guess head gasket could be a problem but hoping not. The car is in Arizona and had no coolant in it when I bought it. I think it hadn’t been run in five or more years. I doubt if it had antifreeze in it in many years.

[Mark L]

If it was sitting for that long with no coolant, then it may just be rust sediment within the cooling system getting stirred up. The last time I removed the block drain plugs on the 259 in my Lark, the antifreeze initially came out looking like brown mud until enough "clean" coolant came down. You might need to remove the block drain plugs and flush the block with clean water from the top and backflush from the drain ports, flush again from the top and let the water drain from the ports, reinstall the drain plugs, then refill the system with fresh coolant. The best way would be to remove the freeze plugs from the block so you can get all the crud out, but that's a lot more work than just removing the block drain plugs.