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| which radiator cap https://www.ausmini.com/forums/viewtopic.php?f=2&t=67389 |
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| Author: | floss [ Tue Nov 30, 2010 8:58 pm ] |
| Post subject: | which radiator cap |
Hey Guys and girls. A quick question. So.... a plus motor, 1275. This should have a 13 lb long necked radiator cap yeah? If you have a long necked 7 lb cap will it get to temperature and then over flow? DC |
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| Author: | 1071 [ Tue Nov 30, 2010 9:16 pm ] |
| Post subject: | |
No.. a lower pressure cap will just allow the coolant to boil at a lower temperature - should it get that hot. A zero pressure cap would allow the coolant (assuming its pure water) at 100C. Anti -freeze and a pressurised cap just raise the boiling point. Cheers, Ian |
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| Author: | TheMiniMan [ Tue Nov 30, 2010 10:06 pm ] |
| Post subject: | Re: which radiator cap |
floss wrote: Hey Guys and girls.
A quick question. So.... a plus motor, 1275. This should have a 13 lb long necked radiator cap yeah? If you have a long necked 7 lb cap will it get to temperature and then over flow? DC Probably , in Australia , yep |
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| Author: | Irish Yobbo [ Wed Dec 01, 2010 7:37 pm ] |
| Post subject: | |
Sort-of on topic: Are there special caps for overflow bottles? I was thinking of making my own overflow bottle, but I wasn't sure that the normal cap would let any coolant back in. |
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| Author: | toolie [ Fri Dec 03, 2010 7:21 am ] |
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I've got an overflow header tank from a moke on my clubbie., works a treat.You put your pressure cap (13lb) on the overflow tank and a flat radiator cap on the radiator.Coolant expands into the header tank and is pressurised then returns to radiator when cool 
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| Author: | Irish Yobbo [ Fri Dec 03, 2010 7:47 am ] |
| Post subject: | |
Quote: I've got an overflow header tank from a moke on my clubbie., works a treat.You put your pressure cap (13lb) on the overflow tank and a flat radiator cap on the radiator.Coolant expands into the header tank and is pressurised then returns to radiator when cool
Oh, ok, that sounds interesting. I was thinking of having the overflow unpressurised, so the radiator drops as usual (pushing the coolant into the overflow), but when it cools back down instead of sucking in air from around the cap, it would suck it back in from the overflow bottle. I wasn't sure if this would work without a special cap though. I might try it my way first and see if it works with a standard cap. As nice as an authentic overflow would be, there is a certain satisfaction of trying something cheap and having it work. |
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| Author: | toolie [ Fri Dec 03, 2010 9:29 am ] |
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I got this info from a radiator tech. I dare say you could just let the coolant expand into the overflow tank without a pressure cap trouble is though if you don't pressurise one end of the setup you could end up with the entire radiator boiling out through your header tank. You have to pressurise the system to allow the coolant to expand and open the thermostat to the block All the books talk about the pressure cap being on the expansion tank particularly the moke |
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| Author: | Irish Yobbo [ Fri Dec 03, 2010 2:24 pm ] |
| Post subject: | |
toolie wrote: I got this info from a radiator tech. I dare say you could just let the coolant expand into the overflow tank without a pressure cap trouble is though if you don't pressurise one end of the setup you could end up with the entire radiator boiling out through your header tank. You have to pressurise the system to allow the coolant to expand and open the thermostat to the block All the books talk about the pressure cap being on the expansion tank particularly the moke
In normal operation without an overflow, the excess coolant just flows out from the cap and down a tube onto the road. I was thinking about having this tube lead into an overflow bottle. When the car cools down, it will (hopefully) suck the coolant back from the bottle into the radiator. Normally it just sucks air from around the cap, and the radiator drops a little. The problem is, on hot days it drops further than usual, and without an overflow it'll stay dropped. If I stick a bottle at the end of the tube, the radiator's still pressurised by the normal cap, so nothing can go wrong. It's just a matter of checking if the radiator will suck up the coolant from the tube, or suck air from around the cap (like it does at the moment). |
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| Author: | sgc [ Fri Dec 03, 2010 3:11 pm ] |
| Post subject: | |
OK, it goes like this: If you have a non-pressurised overflow, it needs to be above the level of the radiator neck so that gravity can feed the fluid back into the radiator as it cools. You need a radiator cap with a drainback valve for this to work. If the overflow is pressurised (like mine which is an MG one I think) then you can place it anywhere. Mine is under the wheel arch, out of the way. With this type you run a pressure cap on the overflow tank, and a flat cap on the radiator. The pressure in the overflow (and the vacuum created in the radiator) forces fluid back into the radiator as it cools, and as long as there are no leaks you're fine. |
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