Radiator Cap

[Bob46320]

its a '79, 998cc A+ standard engine. I have recently taken this car over with all sorts of minor problems following a re-build. I had to replace the thermostat as the old one opened at boiling point, and steam coming out of the rad overflow pipe. Now have a 74 deg C thermostat (summers here are +40 deg C) and new 13psi rad cap.

Problem is that rad water is still being lost out of the rad overflow pipe (rad filled cold up to the fill mark). The distance between the top of the rad spout and the inner seal is 20mm. The distance between the inner top seal of the rad cap and bottom of the rubber sealing washer is 21mm giving a bare 1mm of compression of the spring in the cap.

Also, the old rad cap was marked WAXSTAT - how would that work on a cap as it implies that it is temperature and pressure controlled.

RadCap 13psi 1 Large.jpeg

RadCap 13psi 2 Large.jpeg

[Bob46320]

RadCap 13psi 3 Large.jpeg

[Peter Laidler]

There's an easy answer to your problem Bob. Totally empty your rad and cooling system and fill it with waterless coolant. If you haven't toitally emptied the system you might need to fill it with waterless coolant preparation fluid and run it fior 15 minutes or so.

Drain down the now slightly dilutted prep fluid and fill with wateress. You won't ever boil it, won''t pressurise so you can even forget to use a rad cap (you'll need to, just to keep the liquid in....) It can't boil, so no pressure........

The old sweats among the forum flock baulk at its use but it is in both mine. Drove non stop to Dusseldorf last year in the hottest temperatures and it never missed a beat, never used any fluid

You might reply .....'yes, but I haven't cured my original problem...' You will have by using waterless....... No more burst hoses or sat at the roadside while the rad steams up

As for the used waterless prep fluid. Just pour it into a pot, put it on the stove when the wife is out and allow the water that's been absorbed to boil off for 15 inutes. Leaving the now UNdiluted prep fluid for next time

[Spider]

The Waxstat Cap you have is just the brand of it, it doesn't have a temperature release, only pressure.

With a reach of 21 mm, it does sound light on, usually these are around 23 mm for a 13 PSI cap. This is where I've measured from;-



I don't know what brands are available to you in the UK, however in a Tridon Brand , their P/N is CN13890. You should be able to use that number to find an equivalent in your favoured brand.

The other thing I've always done on the Minis I've owned is fit a header tank somewhere. There's many ways this can be done, if it's a non-pressure header tank (or just an over-flow catch tank), you need a different cap that has 2 seals in it, one on the base like the normal cap and the other on the top of the neck. By running a header or over-flow tank it removes all air from the cooling system, in hotter conditions, this does let the system cool better and it also goes a very long way to reducing or eliminating corrosion of the cooling system. Just about all other cars that BMC / Leyland made had one and in later years, they did eventually find their way on to Minis. I can only guess they weren't fitted for a long while as a cost cutting measure and / or they couldn't work out where to fit one. Our Aussie Mokes had even them from 1968 to the end of production.

Sorry there Pete, but that's one thing I don't agree with you on, though there maybe some types of waterless coolants that might work. I know that Evans stuff is bad news, it's 100% glycol which is a pretty poor at receiving and expelling heat. Most people I know who have tried it found their Minis ran hotter on it and switching back to a 30 / 70 mix of glycol / water fixed their run hot issues. Fir what ever it's worth, in the Mokes, we run a fairly standard system, the only modifications are to do away with the By-pass and a 6 Blade Tropic Fan. Last Year on a trip to Adelaide in summer, it was a week of 40+ temps here, one afternoon it pegged out at 47 deg C, yet the Moke happily only maxed out at 92 deg (and yes, that's dead accurate).

[Bob46320]

Thanks for that Spider, I looked on line at your cap, and the tech note gives a dimension from top of cap to the bottom of the vacuum release valve of 31mm. Assume 2mm for cap thickness plus the thin stainless seal inside the cap, 4mm for the vacuum release valve would give 31 - (2 + 4) = 25mm which would give a better seal.
If there was a fiber/rubber seal under the cap, it would reduce by another 2mm perhaps giving 23mm which would still be better than my 21mm.
Bob

[Spider]

There is a longer reach Cap but beware !!!

The Cap must be matched to the Filer Neck depth. Fitting a long reach cap in to a short reach Neck then sets the release pressure sky high, certainly enough to rupture your radiator.

The one you should use is the short reach cap with your Radiator.

[swifty]

I always vacuum the air out of the system and pressure test for leeks . Also fitted is a MGB header tank . 15lb rad cap on header and plain cap on rad . Minispares two core rad … Shirley

[swifty]

Pressure test

[winabbey]

... and pressure test for leeks.

Always worth doing. I found this in the cooling system last time.

Leek.jpg

But seriously, the common radiators used by BMC in Australia had two neck working heights as Spider has mentioned. The shorter height is 0.767 inches (1.948 cms) and the longer is 1.017 inches (2.583 cms). This is dimension D in the table below.

On the following drawing you can see the Coutts CPC (now Tridon) cap part numbers for each type and for various release pressures. How does your cap compare the dimensions shown for the shorter cap?

AYH2092 Radiator Cap Assembly wm v2.jpg

There may be information on the Tridon website that will help.

https://www.tridon.com.au/products/Trid ... iator-caps

[Bob46320]

That drawing is 'Golden' but a bit fuzzy and feint. BUT I have got the measurements off of it - thanks. Will measure dim A on my caps. My dimension D wavers between 0.748' - 0.787" and the drawing states 0.767 , so in the worst case, the neck is 0.020 too long !
Bob

[Spider]

But seriously, the common radiators used by BMC in Australia had two neck working heights as Spider has mentioned. The shorter height is 0.767 inches (1.948 cms) and the longer is 1.017 inches (2.583 cms). This is dimension D in the table below.

From what I found Doug, the longer neck radiators were fitted to the Mokes (that had the Header Tanks). The over-flow Pipe on these extended well in to the Neck so you couldn't fit a conventional (pressure release) cap, but only a blanking cap.

The early Minis may have also had a long neck (isn't that a bottle of beer ?).

I did a write up a while back in the various caps, including CPC Part nos. here'-

https://www.theminiforum.co.uk/forums/t ... ian-mokes/

[Peter Laidler]

Surely there's no need to 'test' a radiator for leaks because if it leaks....... even with a pinhole you'll see that it's dripping from somewhere!

If it's pressure leaks that's worrying the forum flock, then help is also at hand because waterless ain''t dependent on pressure to cool the system.

It's time to come clean now. I have a VERY minor non-financial interest in waterless coolant in that as it started to appear on the UK market, me and my friend ,James the Chemist, did some trials/tests to ascertain what the claims said were true or just B-S. With access to the large Uni labs and a smaller lab at home ....., the kitchen..... and an engineering workshop we tested this stuff. Hardly scientific I agree. But we made our findings known to the importer, that it performed as said. The actual BOIL point was slightly less that stated.

They refused to identify the chemical contents of the mixture

While we couldn't make Aussie/Sahara desert temps, we were fortunate enough to test run my 69 S, a Frogeye and a 74 Midget on the hottest day recorded in England a few Summers ago. And all was well....... even down to Southampton on the A34. And without a rad cap on the way back.

Yes, we were financially rewarded for our efforts. The £18 petrol costs and the waterless for my 2000 Rover Cooper sport was 'on the house'

Can't say fairer than that as that's been my experience. And I didn't even have a rad or cap or leaking problem and certainly no pressure problem.

Been asked to elaborate on the pressure question. There will be a slight pressure increase but only the natural expansion of a liquid that might pressurise the small air gap in the top of the rad. But negligible in real terms
AND.... what happens if I don't remove all of the previous water? The new now mixed fluid will reach working temp and the remaining water content will do what water does...... Boil off! Leaving you what seems like a leak because the fluid is now lower. Just top it up.

[RichB]

That drawing is 'Golden' but a bit fuzzy and feint. BUT I have got the measurements off of it - thanks. Will measure dim A on my caps. My dimension D wavers between 0.748' - 0.787" and the drawing states 0.767 , so in the worst case, the neck is 0.020 too long !
Bob

Hi Bob,
Did you get anywhere with working this out? I have the same issue. The GRC102 cap isn't quite long enough for the neck of the rad (the seal touches, but wouldn't allow any pressure) and the GRC101 would be much too long I think.

Rich

[Bob46320]

Quick answer is No. In the end, I fitted the old 15 psi cap with its "deformed" seal which is about 1.5 mm longer than the 13psi GRC1111 (21mm from under the top lid and bottom of the seal) which did not seal.
My radiator spout measures between 19 - 20mm from seal face to the top.

The old 15 psi cap has an "A" dimension of 16mm ie measured from the bottom of the lugs on the cap to the bottom of the sealing washer face and 22.5 mm from under the top lid and bottom of the seal.

Two things, was my radiator made by "any old radiator company" and the spout is non standard, being in FRANCE, this could be true and the original problem was down to the thermostat not opening until just under boiling. I now have a 74degree thermostat as we do get pretty hot summers over here.
Bob