Has anyone successfully used the square plastic GM washer jar as a coolant overflow? I wonder about two things:
1-Can the plastic take the heat?
2-Is the inlet diameter on the cap large enough to work properly?
I would remove all of the filter parts and just keep the inner tubing that extends to the bottom of the jar.
Thanks
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It's pretty thick plastic and I've used mine that way for a couple of years now. I bought an extra cap to use for this purpose. A hardware store netted a plastic 90º elbow fitting that was threaded on one side. Any plastic (or brass if you're so inclined) fitting will do as long as the hose fits. I drilled a slightly smaller hole than the thread size and "threaded" the plastic fitting into the cap then ran a hose from the radiator overflow tube.

I didn't bother with the hose inside the washer bottle. I figure when it overflows it might as well dump in the bottle as quickly as possible without going through the little hose as well and I keep a check on it. Naturally, it won't suck the coolant back into the radiator cause it's not really a "closed" system as such. I trimmed the original fluid hose to the wipers so it's not as obvious but still gives a vent for the bottle.

I try not to drive too much in conditions where the washers are really needed so I don't miss that application.

http://www.chevelles.com/showroom/396guy/p001775.jpg

Again Dale, you have the answer, and the picture, to show me what I needed to know.
My biggest concern was that it not melt into a plastic puddle the first time hot coolant hit it.

BTW, does your radiator have a drain valve? I just bought an aluminum radiator from AFCO Racing Products that looks mysteriously like yours, but doesn't have one.
If yours doesn't, how did you address that issue?
How WOULD you address it if it didn't have one?
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I use the washer fluid bottle as an overflow too. I just ren a rubber hose to the plastic cap and left the rubber line attached in the bottle. Haven't had any problems.