What's the best way to do so?
I was just going to get a short length of hose and ram a bolt down the end with
some gasket sealant, and a few band clamps, but whilst in clark rubber I found
some rubber stoppers intended for use on chairs to stop floor damage.
Its a perfect fit over the bypass thing, and some goo and a clamp would hold it very well, but would it still be a good idea to use it as opposed to the other way?
What sort of pressure would it have to retain?
Thanks.

Well, the cooling system holds 13psi, and about 85-95 degrees C.

I welded up the head end of the show, and drilled-and-tapped the water pump, then used a brass plug. Now you can get a water pump without the take-off.

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And also a brass plug for the cylinder head

grh
i dont like that idea of blocking it off completely
there is a reason why its there.
if something fails or a channel gets blocked
water can still circulate through it

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That's why when you block it you have to drill a hole in the thermostat to compensate. Metros and later model Minis didn't have a bypass hose standard.

No, but they had a sandwich plate with pipe, below the thermostat that did a similar thing.
Was on a Metro head I saw.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

block it off it only is one less place for it to leak.
I have built many many motors and none of them have the bypass and i have never had an overheating problem or a blockage problem.

just remember to drill a couple of small 3/16 holes in the thermostat.

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On a slightly diffrent tack......
If I block off the bypass at the water pump and add a heater bypass like the one in the photo.....I don't need to drill the holes in the thermostat do I

Has anybody else done a bypass like this with success

Minimad

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You can take the boy out of the racer.........but not the racer out of the boy!

While we're on the pump topic, which way does the water circulate through the system?
Does the pump withdraw water from the block or send it in?

The pump takes water from the lower tank of the radiator and pushes it into the block.
The original bypass hose lets a bit of water out from the head, down into the water pump inlet- when thermostat is shut. This is to allow the block and head to warm up evenly.
Once the thermostat opens, hot water flows to the top of the radaitor, it goes down through the radiator core to the bottom tank, getting cooled.

If you block the bypass and don't drill a couple of holes in the thermostat too, you have no circulation at all until the thermostat opens.
However, if you have a heater bypass pipe like Mini mad suggests yes it will circulate. But (there's always a but ) when hot, you are dumping hot water straight from the back of the head into the water pump with no cooling.
Experts will tell you this is wrong... but I'm not commenting.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Just drill thermostat holes, it's the right way to do it and really easy...

Best way to plug the hole is drill and tap then put a bolt in there.

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Lillee - 1969 Morris Mini K

Or TIG weld it up.

If you want to plug the hole in the head a 5/8-18 UNF bolt will screw in.
Debate continues whether it's really 18 TPI or 16, but trust me, a 5/8" UNF fits.

I make brass bypass adaptors (last forever, never rust) if like me you want to keep your head unplugged. $20 each plus post.
Use with a bit of good 1/2" heater hose, no problems.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

But then you can't go back

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Lillee - 1969 Morris Mini K

Sure you can, just redrill it...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I'll fill you in on the situation a bit more.
My engine is a A+ one, the old pump has the blocked bypass, and there is
a hole in the thermostat housing for the extra pipe.
The car would've originally had a heater, but I'm not putting one in.

I'm going to take a guess here, as I'm not sure how it worked, but I think the heater
went between the thermostat housing and an extra line off the lower radiator hose.

So I'm thinking I could plumb the thermostat line directly to the pump bypass point,
and block off the lower hose line.

That all works well, but my lower radiator hose has two extra joints.
The second one goes into the heated inlet manifold, but don't know where to
put the hose on the other side to?

Anyone shed light on that?