Water pump surprise

[Sundowner]

Hi,
I started my SPRINT's water pump rebuild job today and on disassembly I had a pleasant surprise.
A previous owner has installed a 12 vane impeller on the pump. (Still haven't extracted it from the block though) Another surprise was when I found that it had a 6 vane cover. Now, I thought that these things couldn't be mixed and matched but I've owned this car for around 7 years now and not had any over heating issues, so this combination, although not ideal, obviously works OK.
The good news is that the cover is pretty much cactus and needs replacing anyway.
I've already asked for an all up part + postage price from Robsport for a 12 vane item.
I'm interested to hear of anyone else's views on this impeller/cover combination and if the 12 vane cover will be any better.
Cheers,
Rob

[gmsclassics]

Hi Rob

Not sure that I've heard of anyone mix and matching impellor and cover on the water pump. In fact most of what I've heard is around make sure you don't. Fascinating though that it works so well!

There are in fact two types of six vane, early and late and again the cover is specific to each.

Given the 12 vane is the last in the series of three types, there would be good reason to suppose it is the best in relation to what the car is designed for. I know we can be critical of British car design in the seventies, but to design a specific cover for the impeller makes it difficult to conceive that using the earlier version might in fact be better!

There has been talk of cavitation in those 12 vane pumps at high revs, almost exclusively in relation to racing. In fact that is what made me move to a Davies Craig electric pump. Another trick used in race cars was to remove every second vane, although I never tried that. However, both my road cars have standard 12 vane and I've never had an issue with cooling on either.

Geoff

[tony g]

Rob, on the 6 vane are they curved or straight veins? Just wondering if a 12 was machined to make a 6

Tony

[Sundowner]

Its a straight 12 vane-d impeller on the pump.
BUT...the cover is for a 6 vane steeper impeller. (well, as far as I can tell, anyway). The angle is a fair bit steeper than the surface of the 12 vanes.
It has suffered quite a bit of cavitation damage, though, that I initially thought was pitting from corrosion.
However, because I don't have another one here to compare it against, I could very well be wrong.
I'll know for sure when the new 12 vane cover arrives, in about 10 days from now. Ahhh....the "tyranny of distance", eh?
Rob

[xvivalve]

The test is to project the angle of the slope of the cover until it reaches the underside of the lid; a 12v will land the other side of the central button, a 6v will land the same side as the central button.

I can send you a serviceable 12v cover for £35 inc postage, if you've not ordered one already? Or £27 if you care to wait for economy delivery...

[Sundowner]

Armed with that info, I can confirm that it is definitely a 6 vain cover.
Simon at Robsport says he's seen a few like that.
I had already placed an order with them, thanks.
Rob