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Non Pressurized Radiator/Expansion Tank Caps

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OldBloke Avatar
OldBloke Gold Member Jim Legg
Napa, CA, USA   USA
1970 Rover 3500
1971 MG MGB GT
1972 MG MGB V6 Conversion
1973 MG MGB "Tagalong"
10 lb radiator caps readily available. Haven't found reliable source for a non pressurized cap for use with my Moss #459-690 expansion tank and stock '71 MGB radiator. Two prior orders have been wrong size. Suggestions (with part #s please)?



"Not all who wander are lost." -J.R.R. Tolkien

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rocannon Avatar
rocannon Platinum Member Frank L
Inconveniently located in the wilderness, OK, USA   USA
1967 MG MGB GT "GT From Hell"
1980 MG MGB "Restored By Photoshop Inc."
Modify a pressurized cap by removing everything except the cap and gasket. Works perfectly.

In reply to # 3660633 by OldBloke 10 lb radiator caps readily available. Haven't found reliable source for a non pressurized cap for use with my Moss #459-690 expansion tank and stock '71 MGB radiator. Two prior orders have been wrong size. Suggestions (with part #s please)?



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TANSTAAFL !



Edited 1 time(s). Last edit at 2018-01-12 04:42 PM by rocannon.

tampaguy Avatar
tampaguy Jack Shea
Elgin, OR, USA   USA
Jim
I have a late model brass expansion tank I wish to install on my 67 GT. Can you clarify the best caps for radiator and expansion tank....thanks Jack

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LannM Avatar
LannM Platinum Member Lann Mauck
Claremore, OK, USA   USA
1958 MG Magnette ZB Varitone "The Queen"
1963 MG MGB
1967 MG MGB GT
I think what you're looking for is a flat cap, Moss P/N 780-126.



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OldBloke Avatar
OldBloke Gold Member Jim Legg
Napa, CA, USA   USA
1970 Rover 3500
1971 MG MGB GT
1972 MG MGB V6 Conversion
1973 MG MGB "Tagalong"
Hey Jack, on my '67 had a stock 7lb and a non pressurized on the expansion tank, but sold it on without looking at the cap closely (I'd had for years) so can't be of help there. Thats the reason for my post as well. Think I'll go with Frank on this one and just modify one of my stock caps laying around.



"Not all who wander are lost." -J.R.R. Tolkien

jewar Avatar
jewar Silver Member John Warlimont
Abbotsford, BC, Canada   CAN
Jim:
Zero pressure is Stant 10203
JOhn


Attachments:
zero pressure cap 001.JPG    50.2 KB
zero pressure cap 001.JPG

Steve S Avatar
Abingdon West, So Cal, USA   USA
Just go to your local Napa and ask for GRC201. Fits perfectly.

Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
Use a closed cap as supplied for the MGC*), disconnect the early radiator overflow hose and mount the later pressured hose to your expansion tank and close that one with a pressured cap.
I performed such a modification and even use the later 15psi pressure cap, with no ill effect. Even this pressure is only about 1 bar: if a rad will take 10psi, it will probably also accept 15psi eye rolling smiley

The old overflow hose is transferred to the expansion tank instead, or you just order a new one, in conjunction with the MGC cap and the pressure hose with MOSS.
See my picture on how it all is mounted; my own expansion tank came 2nd hand via Andy Jenning, UK..... smileys with beer

*) PS I had difficulty to find this part back on the MOSS E site, MGC parts are always difficult to find. GRC126 it is smiling bouncing smiley
BTW, I used a slightly thicker rubber ring from an earlier MGB cap of mine in this MGC cap, its own rubber ring was rather thin and I did not want to bend the ears on its bottom

In reply to # 3660633 by OldBloke 10 lb radiator caps readily available. Haven't found reliable source for a non pressurized cap for use with my Moss #459-690 expansion tank and stock '71 MGB radiator. Two prior orders have been wrong size. Suggestions (with part #s please)?



Edited 4 time(s). Last edit at 2018-01-13 11:24 AM by Donthuis.

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tampaguy Avatar
tampaguy Jack Shea
Elgin, OR, USA   USA
So if I understand correctly, use a nonpressureized cap on expansion tank and 7 to 15lb cap on radiator ? The hose between them should be pressurized Type ? Overflowing hose out of expansion tank, correct ?

Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
No read carefully, just the reverse. Radiator only closed on top keeps an open connection to the expansion tank via the pressurized hose. Only the expansion tank carries a 13 or 15 psi pressurised cap as specified by BL (or 10 psi reused, if you so desire)!

Last statement is correct.....

In reply to # 3661086 by tampaguy So if I understand correctly, use a nonpressureized cap on expansion tank and 7 to 15lb cap on radiator ? The hose between them should be pressurized Type ? Overflowing hose out of expansion tank, correct ?

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Fairfield, CA, USA   USA
There should be one of Dave DuBois' epistles on coolant recovery in the library that would lay things out pretty well.

The flat cap is readily available at NAPA, no need to ship it in.

Only question I have on this is relative height of the expansion tank vs rad header? Can expansion tank be lower or should it be about same height?



1973 Pale Primrose Roadster. A nice 10-footer!
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Steve S Avatar
Abingdon West, So Cal, USA   USA
Height doesn't matter.

Donthuis Avatar
Donthuis Don van Riet
Rijswijk, ZH, Netherlands   NLD
Correct, the coolant passing to and fro the pressurized hose and the pipe internal to the expansion tank ends below the fluid surface. So in both directions, either expanding or contracting the fluid moves correctly. Getting the air out of the system requires slightly loosening the pressure cap after a heating cycle. This way once or twice it will get you air bubbles from rad to tank and out. Refill to max 2/3 after each action, in the end the level will settle to halfway in the expansion tank...

PS There is no need to loosen the MGC cap after filling the radiator. Filling up is normally via the tank.
Removing it later only helps filling up anytime after the cooling system is fully emptied in some engine job..eye rolling smiley

In reply to # 3661202 by Steve S Height doesn't matter.

barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
What is the benefit of an overflow tank on a CBB?

Steve S Avatar
Abingdon West, So Cal, USA   USA
Same as on any other car... It allows the cooling system to remain completely full. Otherwise, as the engine heats up it expels a quantity of coolant due to expansion. The hotter things get, the more coolant is expelled. Upon cool down, the coolant level drops significantly, bringing a bunch or air into the upper tank. And there it stays, where additional coolant could be instead! The expansion tank captures the expelled coolant from the radiator, and returns it as the engine cools.

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