Actually it takes very little liquid flow through the free-hanging valve to make it close (try it). Once it closes it stays closed with the very slightest pressure. It will not open again until all pressure is relieved. I've had them close as the engine was warming up and then very slightly reving the engine.

If your radiator cap has the free-hanging valve you can test if the radiator top tank is full of coolant by merely slightly squeezing the top radiator hose. You can hear and feel the valve go shut. If the top tank is not full and you squeese the hose the valve will likely stay open because the air will not push it closed very easy unless you squeeze the hose fast and hard.

This is how I test mine, no need to remove the radiator cap to see of top tank is full to top.

sorry guys, I was outta town due to work. I was at a jazz fest in my hometown.

What a great compilation of useful info!. I'll recore /replace my rad. Let's see if i got it right this time. I'm using a 4 rows core this time. I plan to increase coolant capacity about 1 gallon with this new core, (I mean, coolant capacity increase due to larger rad capacity, not an additioinal bottle)

Another thing I'd like to ask is (I'm starting another topic?) I'm having an "new" issue with my car: she pukes out one pint of coolant every morning when I cold start her. This issue has developed since I got here. I drove 300 miles cruisin @100 mph, I had a minor bug on the road: I was surpassing a truck and suddenly she lost "grunt" and started to cough-sputt- I parked and looked at everything. I was suspectin some ignition miss 'cuz she started fine when I stepped on the gass but sputtered and wanted to stall right away. Idle was crappy too. I ended up taking the carb appart and spraying it. It was dirty, I got it working and arrived safe. day before yesterday I checked valvle lash, renewed the carb's gaskets and dialed it in again, everything was smooth and nice. I even brought my cam profile to a racer friend and we used a rare lash.. .005 ex and intake but she was purring like a kitten, great power improvement and some temp issues were gone. I parked her at my garage, and yesterday morning (10ªC temp) when i started her, about 5 mins from zero cold start she started to spit water trhu the overpressure relief valvle on the rad top tank. I figured, heck, I overfilled the rad (snce I added some watter before starting my trip) and never did spit again in the whole day (yesterday) this morning I had the same issue. I have no oil in my water or water in my oil. I'm to suspect blown/misaligned head gasket anyways, ain't I? I have laminated steel head gasket, shaved head and decked block, 9.5 or so compression ratio when i first measured my mill. Now I have 10K miles on it. No water comsumption before, I been having some temp issues that comes and goes away. Please, help.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

o yeah, she spitted about 1/8 gallon of coolant yesterday, for about 2 mins. Then today she spitted one pint for 3 mins. No more problems after that "during warmup" issue. I'm desperate...

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Now that's an interesting problem...pukes coolant when warming up, but not afterward. You say you're losing 1/8 gallon (= 1 pint), which really isn't all that much. It could be that you're trying to keep the radiator full right up to the very top, which doesn't work if you don't have a coolant reserve system. Figure: If you fill the radiator right up to the very tippy-top when it's cold, what's gonna happen when the coolant gets warm and expands? Right, it'll have nowhere to go but out the overflow tube.

If you haven't got any other symptoms of a blown head gasket (overheating, constant coolant puking, steam and sweet smell out of the exhaust) I'd guess you're not in much trouble.

Now, if this is happening and you're NOT trying to keep the rad full all the time, that's a different story...

Hey Dan

Thanks for such a quick answer

Let's see

She spitted say a pint the first day and then less than a pint today. May be that I tried to keep it full (overfilled) ain't overheating all the time. No sweet smell. Smells just about right, kinda peperish. nice just a bit rich and advanced, n o sweet smell, no steam whatsoever, just a li'l condensation when dead cold, that fades to nuttin as soon as I run the car 4 minutes.

So, in order to figure if she's spitting the overfilled coolant or just spitting always when cold, I'd have to check it tomorrow, right? I don't going to refill the rad now. I'm waiting till tomorrow morning to see what happens.

Thanks for such a quick answer.

Juan

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Yeah, don't add any new coolant, just keep an eye on it for a few days and see if it stops spitting.

Well, this morning she ain't puked. So I'm guess that I was overfilling the rad (as a matter of fact I was topping it when cold) so everything should be fine.

I'm gona get back hitting on you guys with a bunch of questions about the new cooling system when I get home.

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.