New Radiator Cap


Information and questions on GL1100 Goldwings (1980-1983)
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Aussie81Interstate
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Location: Penrith Australia
Motorcycle: 1982 CX500 Turbo (restoration project)
1981 GL1100 Interstate (sold)
1988 GL1500

New Radiator Cap

Postby Aussie81Interstate » Sun Dec 14, 2014 4:47 pm



I'll post up a picture a bit later - but a question regarding the cap.

Looks like I have an original cap (same one shown in the manual) - so being it is 33 years old - I think it might have served its purpose and in need of replacement, and I purchased another one from my local auto parts store. It has the same pressure rating of .9 or 13 psi as the original.

After letting the bike warm up for a while - the temp gauge seems to show it was running cooler in that the needle measure on the gauge was just above the thicker white mark - maybe 2-3mm. Woud this seem right as with the old cap it sat about half way? I have done nothing else at the moment except replace the cap. It only has plain water in it - as I will be flushing and installing coolant -after replacing timing belts in a week or few weeks time.

cheers



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HawkeyeGL1200
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Motorcycle: 1984 GL1200 Interstate
1981 GL1100 Interstate

Re: New Radiator Cap

Postby HawkeyeGL1200 » Sun Dec 14, 2014 5:53 pm

If the old cap wasn't holding pressure, I'd suspect it was allowing coolant to return to the reservoir making the bike run hotter. Or, at least that's a distinct possibility. A lot of overheating can be directly linked to improper cap performance in any manner of cooling systems tied to internal combustion engines. I've seen it in cars, trucks and even boats that use a radiator (pressurized) system.
I am wrong as often as I am right concerning what is wrong with someone else' motorcycle without having seen the machine in person. Guessing with limited information, as to the source of the trouble, is sketchy at best.

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redbug
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Motorcycle: 1983 Gl1100I
1986 Harley FLHT

Re: New Radiator Cap

Postby redbug » Sun Dec 14, 2014 8:42 pm

Did you check for air in the system? You know I read warmer than cooler so I correct myself. My gauge reads about the same place as yours now so I think its a win. I would cycle it through till the fan comes on and see how it cools down. When you do your belts and add anti- freeze, you will have a reference mark. Sorry for the confusion.
Last edited by redbug on Sun Dec 14, 2014 10:36 pm, edited 1 time in total.
" Ridin on Tulsa Time "

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Aussie81Interstate
Posts: 683
Joined: Thu Nov 27, 2014 2:34 am
Location: Penrith Australia
Motorcycle: 1982 CX500 Turbo (restoration project)
1981 GL1100 Interstate (sold)
1988 GL1500

Re: New Radiator Cap

Postby Aussie81Interstate » Sun Dec 14, 2014 9:15 pm

Haven't been able to check for air in the system yet - but will do that in the next day or two. I don't think there is any air trapped, have not topped up the expansion tank yet. With the cap not holding the pressure I think it would run a bit hotter - as the expansion leaves less volume to keep everything cool - and then sucks the volume back when it cools.

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HawkeyeGL1200
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1981 GL1100 Interstate

Re: New Radiator Cap

Postby HawkeyeGL1200 » Sun Dec 14, 2014 9:23 pm

A poorly fitting or working radiator cap also won't allow the cooling system to develop the designed pressure at which is should operate. Lower pressure means lower boiling point for coolant. When the coolant is allowed to boil at a lower pressure, it can't remove heat as well. If the coolant boils in contact with the metal it is supposed to cool, tiny steam bubbles form. Steam is a poor heat remover, unlike water which is a pretty good remover of heat... so these little steam bubbles can't remove as much heat from they metal they're in contact with, which raises the engine operating temperature. Once the system pressure is restored, the water in contact with engine parts no longer will flash to steam allowing for more heat removal and cooler operating temperatures overall, as heat is dissipated by way of cooling fins in the radiator and we never even know all this stuff happened .... vapor pressure being raised, the heat transfer is more effective than operating at atmospheric pressure...

Or, at least that's how I understand it to work.

Aussie81Interstate wrote:Haven't been able to check for air in the system yet - but will do that in the next day or two. I don't think there is any air trapped, have not topped up the expansion tank yet. With the cap not holding the pressure I think it would run a bit hotter - as the expansion leaves less volume to keep everything cool - and then sucks the volume back when it cools.
I am wrong as often as I am right concerning what is wrong with someone else' motorcycle without having seen the machine in person. Guessing with limited information, as to the source of the trouble, is sketchy at best.

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Aussie81Interstate
Posts: 683
Joined: Thu Nov 27, 2014 2:34 am
Location: Penrith Australia
Motorcycle: 1982 CX500 Turbo (restoration project)
1981 GL1100 Interstate (sold)
1988 GL1500

Re: New Radiator Cap

Postby Aussie81Interstate » Sun Dec 14, 2014 11:33 pm

Hawkeye,

Awesome information - getting way too technical savvy for me - but I get the gist of it. many thanks.

charlie

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Aussie81Interstate
Posts: 683
Joined: Thu Nov 27, 2014 2:34 am
Location: Penrith Australia
Motorcycle: 1982 CX500 Turbo (restoration project)
1981 GL1100 Interstate (sold)
1988 GL1500

Re: New Radiator Cap

Postby Aussie81Interstate » Mon Dec 15, 2014 4:57 am

I'll try to load some photos

If you look closely there is a chunk missing from one side of the rubber seal - and then another shot where it has stretched.
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