When installing a blanking sleeve do you block off the bypass hose between the head and water pump?
What can go wrong if the bypass hose is left in place?
I noticed that the sellers of the blanking sleeves recommend to block it off.

Bypass is only there to allow water circulation in the head and block during warmup, when thermostat is fully closed.
If you are fitting a blanking sleeve (and therefore no thermostat) the bypass is redundant, so feel free to plug it up.

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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.

When I purchased my car it had the blanking sleeve already fitted and the bypass hose still in place. Should my engine run cooler after I block off the bypass?

Won't make any difference.

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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 will just leave it alone then. Knowing my luck if I stuff with it - it will start to leak.
I was trying to work out why the websites selling the blanking sleeves were saying that you need to blank off the bypass. Maybe so they can make an extra buck on the blanking plugs.
Thanks Doc

I figured one follows the other.

Remove the thermostat to suit issues with water flow in race cars, and plug the bypass to remove a weakness in the cooling system, and simplify headswaps.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Call me old fashioned but I would just stick a thermostat in it.

I can't see the blanking sleeve working properly on every engine. (or any engine!)

I agree, they are really just a race part.
Once the thermostat is gone, warmup will be slow and you won't have control of the temp it runs at.

I have one here, it's sitting in a drawer...

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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 had one in my rally Cooper S so I could block the bypass. Main reason was to avoid having to fix a bypass hose failure while in the middle of a pine forest at 3 am on a Sunday morning.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Yep, I'm a convert too, always run a thermostat these days, including the race car.

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Steve

Thanks for the input everyone.

I was trying to diagnose a cooling issue my car had before it went into storage 10 years ago. And as I live 2500km away from it at the moment I am doing it from memory. I have given myself a 2 month window to get it back on the road so I want everything worked out before I start later this year. I know it needs all the brakes refurbished and clutch hydraulics redone. Fuel pump, battery, and a decent service.

Not sure if I should get it rego'd in QLD before it goes to S.A or wait to get it down here. I don't want to put flares on it and I have a feeling that S.A will want the flares. They did back in 1969.