Radiator Cap

[Bensdexta]

Just checking out my rad cap, see pic, Top is marked "Turn Down Tight" "Remove Slowly" AC F4 RB-5, and a large "4"


and pic of the underside also showing the fibre washer


I think it came off a French Dexta so I guess it is a 4lb pressurized cap by AC.

I tried to test it by blowing into the valve at the bottom of the cap and I detect a slight leak. But perhaps i should give it the benefit of the doubt and wait to test it on my tractor to see if it leaks?

I did spot these on ebay:

A stainless steel radiator rad cap 4LB Fah-Ler caps claims to be "POLISHED LIKE CHROME- NEVER RUST"
Has anyone tried one or got a better repro cap?
TIA

[tom lad]

bought mine from a..........
works fine

[Bensdexta]

bought mine from a..........
works fine

Hi Tom, is it a pressurised cap, 4lbs?

[tom lad]

erm ?


i'll check

[tom lad]

no mention of pressure on it m8 when i loosened the cap it hissed , tractor not run of a few days so i say it was pressuriesed ??? , but i dont know
the caps on my old tvo fergies look more like ur one , they are pressureiesed so the water boils hotter .
the cap on her wen i got it said OIL add here or some thing like that , it did fit .

tom

[Brian]

Some Dextas here, were fitted with a pressurised cap like yours Ben. We sometimes changed them if the tractor was going to be doing hard work. 4psi is correct.

Toms cap is made out of pressed silver paper!
I looked at quite few suppliers before I bought one for Dotty, all made by the same company. Nowhere near the Quality of the original. Think I would have left the Oil cap on.

[Bensdexta]

I looked at quite few suppliers before I bought one for Dotty, all made by the same company. Nowhere near the Quality of the original.

Brian, Where did you get your cap for Dotty?

[Bensdexta]

Thanks for the pics, Tom.

Just found this by BarryM on the old site, so it looks like a Major cap will also fit.
"All export tractors were fitted with pressure release radiator caps. Both the Dexta and the Major were the same.
Part No. E62A 8100 7lb. release was used for temperatures above 110 degrees F.
Part No. E62A 8100B 4lb. release was used for temperatures between 90 degrees F and 110 degrees F.
Part No. 528E 8100 was a non-pressure release for the home market and this cap was interchangeable with the fuel cap."

It appears that a Dexta/Major 4lb cap will also fit XK 120 52-54 (part#C3455), XK 140 1956 (large type) Mk7, Mk9 Jaguars, P4 Rovers and 56-64 Ser1 & Ser2 Landrovers and Willys CJ2a jeep. Fah-ler makes an AC look-alike - has anyone tried one??

[tom lad]

no prob

[Bensdexta]

no prob

Don't worry about Brian, he's a pessimist!

[Brian]

Not a pessimist at all Ben, just pi**ed off with the quality and price of parts offered by after-market suppliers. I saw the cap that Tom bought and actually bent it in my hand, you will also note that it is not fitted with the fibre ring to seal it, yours has come unstuck but it can be refitted.

I bought some wheel bearings for Dotty a month or so ago. I am trying to go around all the suppliers for parts, just to get an idea of quality and cost out there. The wheel bearing were OK but the seals did not fit the stub axle. I contacted the supplier but still have not heard back.

It was one of the other companies that supply parts, usually they are very good but not in this case.

I got my cap from Sparex, I have had it about a year now and it is worn out! the holding down tags bend.

I am on my fourth Dexta ignition switch! Dotty is used fairly often so the switch gets a bit of use, in every case the barrel has snapped. I have fitted a metal one this time and will report on that after a year.

[Bensdexta]

Not a pessimist at all Ben, just pi**ed off with the quality and price of parts offered by after-market suppliers. I saw the cap that Tom bought and actually bent it in my hand, you will also note that it is not fitted with the fibre ring to seal it, yours has come unstuck but it can be refitted.

It's good to be a pessimist sometimes - an optimist is someone's who's not aware of the extent of his problems

Ref the fibre washer, it lives in the filler neck, pretty certain that the nubs around the filler neck visible in Tom's pic are to retain this washer.

I'm coming to the conclusion that the difference between AC RB-5 and RC-5 (AC# 850799) caps is that the former like mine, have a separate fibre washer and the latter has an integral rubber washer like Tom's. I read on a Jaguar site of a problem with some of the latter caps catching on the nubs and not seating properly.

I agree about the variable quality of parts. All the suppliers I have tried are capable of supplying poor ones - just the nature of foreign made parts. And just because the last batch was OK doesn't mean the next batch will be, so it's constant battle - we are the QA dept! Fortunately we can just send them back. It pays to hunt around and ideally find 'new old stock' originals, like the ignition switch I found. Look forward to hearing how your metal one lasts.

[Bensdexta]

Tom, Do you have a red fibre washer fitted in your filler neck - or is that rust??

[russelm]

Thankfuly my original cap is still serviceable and polished up rather well once all the paint and muck was removed.

Trouble is I dont have a nose cone to attach it to, well I do but its off a super dexta and has quite a bit of filler in it!

[Bensdexta]

Mark,
Is your original cap like mine with separate fibre washer, or like Tom's with integral rubber washer? Have you tested, your cap If so how?

For a nose cone, keep looking on ebay, they do come up - that's were I got my original one a couple of years ago for £100. But be aware there are two shapes of original cone, later ones have more slopey cheek panels like a Super D, whereas aft edges on the earlier ones are more vertical with a curve at the top. I think the changeover was prob about mid 1962, when the minimec pumps were fitted.

[tom lad]

sorry for delay m8
the fiber washer , or wots left of it is in the filler neck . i noticed bits of it stuck to the rubber on the cap when i removed it to photo .
dont know if it should be loose or if mines just stuck , welded with age /badness. . but it must be sealing as it hissed when i loosened it .
the coolant level is never full the top , but just visable on the bend in the hose , normal expansion i tink . it dosent loose water .

my cap is fine , a few years old now
it is really phoo that we cant buy parts of consistant quality for our beloved machines

[Bensdexta]

The fibre washer, or what's left of it is in the filler neck. I noticed bits of it stuck to the rubber on the cap when I removed it to photo.
Don't know if it should be loose or if mine's just stuck, welded with age /badness. . But it must be sealing as it hissed when I loosened it.
The coolant level is never full the top, but just visable on the bend in the hose, normal expansion I think. It doesn't loose water.

Technically you shouldn't need the fibre washer, as it's a hangover from the earlier design of cap; it should be loose, just sitting under the nubs around the side of the filler neck. But if it's working OK suggest you leave it alone. Yes I think it's normal for the coolant to be down from the top, as you say to allow room for expansion.

[Bensdexta]

Just to summarize the story behind our radiator caps, it appears that the 'original' cap used on Dexta and Major was made by AC, type RB-5, 4lb pressure, with a separate fibre washer that sits in the filler neck under the nubs.

This cap appears to be a 1940s era AC as used on Ford Automobiles and Willys Jeeps. The Ford version of the Jeep was called Ford 'GPW', manufactured from 1941-45 for which the rad cap was Part No. FM-GPW-8100-A, very similar to our tractor Part No E62A-8100-A. The original AC Cap used by Ford and Willys, on the Jeeps and Ford Cars/Trucks has evolved into the AC Delco RC-5 with rubber seal attached to the bottom of the valve (said to be a much better set up). So it is best to install the later AC RC-5 (or equivalent) and remove the fibre washer from the neck. Original NOS AC caps come up on ebay from time to time ( I got an RC-5 from USA) for about $15 plus shipping. Alternatively one such equivalent which is said to be good, is made by Fah-ler (eg see Queensberryc) - anyone tried one?

[Mark]

Ben, I have a 1959 and it has the AC 4lb cap with the washer, it was loose like yours before the overhaul, but I glued it back to where I thought it was originally. It hasn't given me any problems so far.

[blue32]

I am on my fourth Dexta ignition switch! Dotty is used fairly often so the switch gets a bit of use, in every case the barrel has snapped. I have fitted a metal one this time and will report on that after a year.[/quote]

Yes Brian...I also know this about bad ignitionswitch,es. - One day Id even pick up again a old switch who didnt work anymoore (it had sitting on the tractor for mybee 50 year,s or so ??). well, I,d took it and soil it with thinner at first for a while and so I,d blow it clean with airpressure and soil it again untill the thinner was almost clean...after id sprayed with W-40 and blow it dry again, and mounted up the wires again, and it worked - - After I did also sprayed another ignitionswitch with W-40 (a new one who also didn,t work properly, and blowed out with air pressure after again, and this switch also worked fine after, so I will also repeat this from time to time... - i think the ign.switch should be covered from rain and so, becouse of water goes insides keyhole too.
blue32.