Radiator cap poundage

[jagnut66]

Hi,
My car seems to have come back from Australia with a 7lbs Radiator cap fitted, now I've flushed her through (and cleared out the back waterways) I intend to refill with anti-freeze and add a thermostat and temp gauge.
Am I okay to stick with a 7lbs radiator cap or will this cause me problems?
Many thanks,
Mike.

[IslipMinor]

I'm sure there will be lots of opinions on this!

Basically the higher the cap poundage the higher the boiling point of the water in the system will be - the table below shows the difference between cap pressure and boiling point:
[frame][/frame]
I run a 13lb cap to give as much headroom between the running temperature and the boiling point as possible. Never had any problems with hoses or gasket leaks, but of course a higher pressure will find any weaknesses earlier than a lower one. To my mind that is a good thing!

[jagnut66]

Hi,
Is that with a standard radiator?
Best wishes,
Mike.

[bmcecosse]

No need for more than 4lb cap in UK (assuming non-competition use) -the higher the poundage the more risk of causing a leak. And the Minor is grossly overcooled anyway for UK use. But your 7 lb cap won't cause any great problems. But why do you think it needs a thermostat - does it not have one fitted?

[IslipMinor]

Mike,

Yes, the one from 1958 until a few years ago, when the core fins were seen to be gently rotting away - no leaks, despite a 10lb cap.

It's now been re-cored with a 'modern' core, but with the original top and bottom tanks and the later 'short' neck to give a wider availability of caps - now has 13lb.

You say you need to fit a thermostat - surely it has one fitted already? If not, and no 'blanking sleeve', the cooling will be very poor, and even a 7lb won't be able to overcome that.

[jagnut66]

Hi,
The car came with a thermostat housing but I found no thermostat inside it.
The reason I've fitted the Marina style one where the sender screws into the top of the housing is that there is no threaded hole in the engine for a temp sender on my 948.
I intend to fit a temp gauge in due course, as I like to see what my engines running temp is.
A lot of local members are advising fitting the 4lbs cap, so I will go that route, though I only have my original 7lbs cap for now.
Best wishes,
Mike.

[bmcecosse]

Have to wonder why the thermostat had been removed.....usually a 'bodge' to disguise overheating/blowing head gasket.If you use the car in winter fit an 84/88 , for summer use only a 74 is fine.

[jagnut66]

Hi BMC,
Just cleared the back waterways and renewed the head gasket anyway, I've spotted an 88 degree thermostat on eBay, so I'll get one for when it gets colder.
Best wishes,
Mike.

[jagnut66]

4 lbs Fahler cap now fitted, however when I last ran the engine after my last post I noticed that the radiator has sprung a leak post engine flush.......
Not a large one as far as I can tell but enough for it to have to be replaced sooner than I'd hoped.
I will try K seal for now, as I don't have the £80 odd spare at present that it will likely cost me to replace it.
Damn shame though. I doubt there is anywhere round Mansfield that will / can repair it for a reasonable price.

On the plus side the engine bay looks a bit tidier than when I bought her:
As bought:
[frame][/frame]
Engine flushed, cooling system flushed / unblocked, replaced head gasket, new oil and fresh water (with anti-freeze/ coolant mixed in it this time!!), heater fitted, wiring tied up / replaced (more to do there), new HT leads and distributor cap, replaced thermostat housing for one that accommodates a temp sender, 74 degree therostat fitted and a bit of a repaint........[frame][/frame]

A little effort at not much cost is so worth it in my view, now I'll not be so embarrassed to lift the bonnet!
I do love Halfords Satin Black..............
............. Shame it can't fix radiators...........
.......two steps forward........
Best wishes,
Mike.

[bmcecosse]

You should throw away that fuel filter - no need for it, and it can cause 'the vapours' in hot weather as the pump struggles to pull fuel through from the low mounted tank.