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MG MGB GT V8 Factory Originals Technical - NGK Plug heat range selection, coolant sealing?

I just did a complete rebuild of my '63 Buick 215. about 10.6:1, stock cam, Edelbrock 1404, pertronix w/hot coil. It really runs great compared to when it was worn out last year. Before I had BP6ES and they were oiled. I started the break-in with a hotter BP5ES and they look white and clean after a few hours on the new engine.
Question: I read where each plug has been popular with this crowd. If I stay with the hotter plug, am I taking any chances or is it like running premium gas in a low compression engine, no benefit?
Next question: On the first start, it overheated and the core plugs spit out coolant. Now they weep a little since I have the coolant topped off and running 190F. They seep about one drop per day after running, not enough to drip but it's still a pain after all I did to make this perfect. Do you guys recommend anything to add to the coolant to seal the system or should I just let it run and hope corrosion will fill the gap and seal itself...
SJS Steinhauer

I don't believe that overheating caused the core plugs to leak - just a coincidence. I can't remember which type of plug this engine has - cup-type or disk and a dimple. Regardless, I would be nervous that a disk-type would pop out sometime, although a cup-type can as well. How many plugs do you see leaking? If more than one, I'd be very uncomfortable about proper installation. What about the two on the rear of the block?

If two or more are leaking, I'd pull the engine and replace them all. If just one, I'd try to replace it in situ.

Second choice is to use something like AlumnaSeal. Bypass the heater, and use clear water, go about 100 miles and then flush the system completely and put antifreeze mix back in. Don't forget to hook heater back up. Because this engine is aluminum, don't leave plain water in for long.

Wayne Pearson

I agree with Wayne.

I don't expect any leak to ever fix itself.
If one plug is leaking and the others are fine then remove and replace in the car.
If other are showing the same signs then replace them all.
One instance of overheating should not pop the plugs out especially if they are new and have been recently and correctly installed.

If the hotter range shows no signs of running hot then I would leave them there.
Check them again after breaking the engine in and see how they look.

Peter Thomas

The plug temp is simply an indication of it's capability to transfet heat to the cylinder head. Hotter plugs have a smaller transfer area. A new engine would tend to run a bit "oily" until the rings and bore are properly bedded in. The plugs should be OK but watch for them cracking the insulator and burning the electode if they are running too hot.
I know what you mean about the core plugs, my newly rebuilt engine has one that drips, and OF COURSE it's the one behind the engine mount!!!!
Allan Reeling

This thread was discussed between 11/07/2009 and 17/07/2009

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