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I have a set of four Accuspark AC9C three point plugs that I bought for my HA recently at a car show.
Advertised as superior starting, which they undoubtedly did, BUT the engine ran extremely hot after about 50 miles, although not boiling, and I didn't lose water. Everything in the engine bay was red hot!!!

These are obviously for a sports type engine, or one that runs at higher temps a 1057 viva!!

Put the old NGK's back in and fine, no problem. That will teach me!!

Anyway, if they are of use to any of you guys with sportier engines, you can have them for six quid posted!

What's probably happening is that the 'better' spark plug is igniting the mixture on a larger front, 3 sparks instead of 1. This will cause the mixture to burn faster and more violently and all the mixture is burnt before the piston is far enough down the bore to turn that energy into torque. That energy then becomes heat energy instead of torque.

An experiment might be to retard the ignition a couple of degrees and see if you can reap the benefits of the extra torque - fuel economy and better acceleration - as well as reduce engine temperature.

I have these plugs in my saloon & have been having problems with overheating/ boiling over, will try David's suggestion & retard the ignition a little & see what happens

Keep us informed. I like a bit of tinkering.

A normal 8.5:1 compression ratio engine with an old fashioned chamber design can take up about 52 to 55 crank degrees to burn a light throttle mixture at 3500 rpm and gain maximum torque - about 42 BTDC (combined, static, mechanical and vacuum advance) and 10 to 15 after TDC. If the mixture burns faster and finishes at say 7 to 12 degrees ATDC you've lost 3 or 4 degrees of leverage. The engine hasn't pre-ignited because the burn started at the correct time, so there is no pinking or detonation but you still get more heat and lost torque.

So, if you take 2 or 3 degrees from BTDC and add it ATDC you re-gain that leverage but with a more powerful explosion, that equals more torque.

It does not work like that. A sparkplug can only ignite at one spot each time. It does not matter how many electrodes you have the spark will occour where the conditions is the best.
The reason for having more electrodes in some engines is to get at least one or two electrodes towards the combustion chamber.

I'm running with the NGK's now, and it is much better, and cooler, so I think I will put it down to experience and continue.

Anyone want the Accu's? Only done a few miles! Open to offers??