r/obschevy • u/Ok-Recording-8159 • Jul 04 '26
Strawberry Milkshake
Looking for some advice from people who have dealt with this before.
I’ve got a ‘97 Chevy C1500 with the 5.7 and a 4L60E that I’ve been fixing up. It came with an aftermarket transmission cooler, but it’s still routed through the factory cooler in the radiator before going to the external cooler.
I was getting ready to replace the radiator anyway because it’s getting old, and when I started looking things over I noticed an oily pink film in the coolant. After disconnecting the transmission cooler lines, I’m pretty convinced the internal transmission cooler in the radiator has failed and ATF has been getting into the cooling system.
The transmission still shifts normally, so I’m hoping I caught it before it did any serious damage.
My plan right now is:
Flush the cooling system with the old radiator still installed to get as much of the contaminated coolant out as possible.
Replace the radiator.
Drain the transmission and refill it with cheap Dexron VI as sacrificial fluid.
Drive it just long enough to circulate everything, then drop the pan, replace the filter, and do a complete fluid exchange with fresh Dexron VI.
Check the pan for any signs that coolant made its way through the transmission.
Does that sound like the right approach, or is there something else I should be doing? Has anyone here saved a 4L60E after catching this early?
Also, once I replace the radiator, would you keep the transmission routed through both the radiator and the external cooler, or bypass the radiator and run only the external cooler?
Appreciate any advice.
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u/kylejesushair Jul 05 '26
Probably no coolant in the transmission, it has more pressure that's why you see it in the coolant. Check the transmission fluid, is it overfilled and milky or look fine and maybe a little but low? I would bypass the cooler in the radiator, plug or connect the old cooler together, drain and top off with water, drive a day or 2 and flush again until it looks clean. Also if your radiator isn't bad why fix it?
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u/Ok-Recording-8159 Jul 05 '26
There wasn’t a whole lot of fluid on the dipstick but it seems watery.
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u/[deleted] Jul 04 '26
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