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MG Midget and Sprite General - Why does Daphne fart?

Sarah's sprite has this slightly embarassing habit of "letting rip" from the radiator overflow everytime she been for a bit of a run. When the radiator's been topped up you get some water expelled with the fart, but it still does it after all the excess has been chucked out. Whilst vaguely amusing in a purile sort of a way, is there an issue we should be addressing?
Mothy - '65 GAN3 and '65 HAN8

Tim. Other than checking out the radiator pressure cap to make sure it is operating at the correct pressure, I see no problem. When the engine has been well used, going up to the top of its normal operating temperature, then the engine is shut down, the water quits circulating. Hence, the static water heats up to a higher temperature, increases the pressure in the cooling system and, if this pressure is greater than the pressure rating on the radiator cap, it burps.

A higher pressure cap will handle the extra pressure better and increase the boiling point of the coolant mixture. It will, also, place additional strains on the hoses, radiator, and heater which may cause leakage from various joints or the failure of the radiator or heater matrix.

Les
Les Bengtson

possibly pressure cap faulty

do you use coolant/antifreeze all year round?

ETA: les posted as I was typing - question still stands though
Nigel At

Yes, we use coolant / antifreeze all year round, although don't know if PO did. Rob, if you read this in passing, did you?

So to clarify, the issue is probably that the radiator cap needs to vent at lower pressure, so replacing the radiator cap may help? It does fit very tightly compared to the radiator cap on the midget (which is also a 1098).

This is our first spridget (indeed our first classic) that has ever had radiator flatulence...
Mothy - '65 GAN3 and '65 HAN8

no, you want the correct pressure of cap fully working and to let the car find its own coolant level (as long as it doesn't go too low as this would suggest a problem)

you don't really want to top up with tap water better to use premixed coolant (at the correct mixture ratio with perhaps distilled water)

you might also consider adding something like Bars - http://www.barsleaks.net/products.html#Cooling System Products

or if you're not sure about previous and present coolant or it's age you could consider a clean and flush of the whole coolant system and then refill with fresh coolant

this might help with the flatuance too

also if you have an overflow pipe that goes to low level you may not hear it

Nigel At

how do you know if it is the correct pressure of cap? should I be looking out for something on it?
Mothy - '65 GAN3 and '65 HAN8

Hi Mothy, I believe that the 1098 uses the same cap as the 1275 which should have 7lb somewhere on the top of the cap.

Mark
Mark Whitmore

make sure you have the longer cap for the longer neck of the vertical flow radiator
Onno Könemann

just thought of it
Switch the cap of the sprite to the midge.
If the problem switches then the cap is the problem...
Onno Könemann

yes it'll be on the cap and it is 7 lb same as the early 1275s, later 1275s like mine take a 15 lb

if you're in any doubt about your present cap change it they're only abot £3
Nigel At

Something else to consider, is a worn out hose, sometimes a hose can look fine on the outside, but kjusr trash on the inside


Several years ago, my truck rad would completely suck in on its self and colapse once shut off after it ran for a while....the hose looked fine, I replaced it....issue solved

So if not a $7.00 cap, might look to a $12.00 hose next.


Prop
Prop

Ooops, sory I forgot to mention that I have an early 1275 with the vertical flow rad.

Mark
Mark Whitmore

Tim. Radiator pressure caps are tested with the same pump device used to pressure check radiators and cooling systems. There is an adapter having two female ends, one of which the radiator pressure checker hooks too and the other that the radiator cap hooks to. Hook up the two, pump up to pressure slowly and see at what point the cap vents pressure.

The radiator pressure caps have a spring to hold the gasket against the inside of the filler neck. Over a period of time, this spring can weaken, giving a lower than rated pressure release. Even some of the new caps, fresh out of the box, will not hold to the cap's, supposed, rated pressure. Any professional mechanic should have such a device and should be willing to test your cap for a very nominal fee.

Les
Les Bengtson

If "Daphne" farts its time to change the name of the car into Dave or Dan, no lady farts in public so it must be a bloke.
For a Dave its quite normall to fart in public so its no longer an issue then...

Amazing how easy it sometimes can be to solve issues. ;)
Arie de Best

Arie, as my grandmother used to say, "where e'er you be - let your wind go free" - it's a family trait!!

Its definitely a 7lb pressure cap, all shiny and new. I've swapped it for the old original one from the midget and we'll see if that cures her flatulence.
Mothy - '65 GAN3 and '65 HAN8

a good idea of Onno's to swap the caps just check both are 7lbs

I've heard that saying and grannys do seem to apply it :)

Nigel At

Well, been to town and back, and Daphne doesn't fart when using Sebrina's cap!

Mystery solved - another item to add to the Moss / Minispares shopping list...

thanks folks
Mothy - '65 GAN3 and '65 HAN8

Make sure you buy the correct long cap as the neck on the vertical flow rads is longer than on the later ones
Onno Könemann

right handy having two cars that share components

I'd have thought a pressure cap could be got from local motor factors (don't know if 7lb is a difficult size to get)

no disresepect to you, and we've all done it or more precisely not done it - check the bl**ding obvious first

easier with hindsight I will admit :)

as put earlier don't just assume because it's new that it can't be faulty but once you're sure the new cap works correctly put on an overflow pipe if you haven't already got one and let the car find it's only level then it's just the usual regular checks

coolant loses some of its protective properties after a number of years even if it keeps the anti-freeze so at some stage a change of coolant will be required, that's agood time to clean and refurbish the whole of the coolant system

notes can be provided on request :)
Nigel At

Onno, Moss show it as the same part number for all models - is this wrong?
Mothy - '65 GAN3 and '65 HAN8

I'm not sure what Onno means but by the factory parts catalogue shows just the one GRC101, which MGOC have at £4.03 - if local factors have it I suspect it'll be nearer £3
Nigel At

I think Onno means a local auto parts store....which I was thinking also....its not an un-common part, save you $15 in shipping cost, on a $7.00 part
Prop

Hmm i remember something about the vertical flow rads being different I'll check my source when i get home
Onno Könemann

Okay got it.
It is in our own Daniel's book on page 65.
In short the verticalflow rad cap is designed for a 1inch deep neck the later types are for a 3/4inch deep neck.

So make sure you get a cap for the verticalflow rad and not one for the cross flow rad.
I do not know if any generic 7psi cap will be suited
Onno Könemann

Onno, that makes a lot of sense as I think the Sprite's cap is a later 3/4 inch cap as it is a lot harder to fit than the Midget one, which is an original. Rob Armstrong's kindly going to pick one up for me from minispares tmw.
Mothy - '65 GAN3 and '65 HAN8

Better out than in, my Gran used to say.
Shawn

So Onno is absolutely correct. Despite the parts numbers in the Moss catalogue being the same, the 7lb caps for vertical rads are different from the 7lb caps for the crossflow rads. Luckily managed to find a NOS one on fleabay.

Left to right - Sebrina's original cap, NOS one from fleabay, Daphne's wrong crossflow one

Mothy - '65 GAN3 and '65 HAN8

showing the height differences (the crossflow one is taller):

Mothy - '65 GAN3 and '65 HAN8

gratuitous engine bay shot with shiny new radiator cap:

Mothy - '65 GAN3 and '65 HAN8

Tim,

"where e'er you be - let your wind go free"..... 'nuff said!!

David
David Wigley (MK2 Sprite)

Tim,

It has what looks like the ST badge on the rocker cover (BMC Special Tuning) do you know what has been carried out ?

R.

richard boobier

Hi Richard, we have a full engine spec, stage 2 fast road on a 1098, but it wasn't done by Leyland ST, I'm afraid. I'm guessing the rocker cover sticker's an aftermarket styling addition by the PO...

still, the Downton Austin 1300 which this Sprite replaced had a genuine BMC Special Tuning rocker cover badge and genuine Downton / Special Tuning parts and paperwork - that was a beautiful engine!

http://www.flickr.com/photos/79267312@N00/3298229830/in/set-72157614184339455
Mothy - '65 GAN3 and '65 HAN8

I'm lost I thought it was 7 for vertical and 15 for cross
Nigel At

I don't know Nigel, I was just going on Ole's comment! Maybe I misinterpreted and the difference is between 1098 vertical rad caps and early 1275 vertical rad caps? That might make more sense...

Anyway clearly it was the wrong type of 7lb cap for a 1098 and now it has the correct one - and I just wanted to show that there are different types of 7lb cap out there which clearly aren't fully interchangeable.

We'll just be glad not to have everyone staring after you park up and a massive farting noise rips out as you get out of the car :o)
Mothy - '65 GAN3 and '65 HAN8

This thread was discussed between 18/08/2011 and 03/09/2011

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