The automotive trade press has been dicussing this topic for many, many years. Namely, the problems with the Stag cooling system that caused the engine to overhead and the heads to warp. From the many articles I have read and the many knowledable folks I have spoken to, this was not an inherent design flaw, but more a symptom of poor build quality, followed by even worse ongoing maintenance.
The root cause, in many cases, was that casting sand was not fully flushed from the block during production. As the engine was in use, the casting sand migrated into the radiator and slowly silted it up, greatly decreasing it’s efficiency. Alongside this, the inherent electrolytic reaction between iron and aluminum at the heads also became a problem if the coolant didn’t contain inhibitors that prevent it.
If the radiator and coolant was regularly flushed / cleaned / replaced, then these V8s ran fine, and of course sounded georgeous with that off-beat firing order.
Anyway, it was time to refurbish mine. I removed the radiator and flushed it clean inside, then gave it a coat of paint to tidy it up along with the air intake duct above it. Whilst the radiator and pipes were out of the way, I also painted the inner side of the front valance and the headlamp panels.
Another issue with the Stag engine (not mentioned above) is the positioning of the waterpump. If the cooling system is kept in good order then this feature of the design doesn’t present itself. However as the car ages and the pipe joints get a little worn and tired, then air can leak into the cooling system. The water pump happens to be the highest point in the circulation system, so this is where the air ends up. Spinning a dry pump never ends well.
To help prevent the above, I have purchased a complete set of new hoses and a StagWeber Header tank, alongside the fresh anti-corrosion anti-freeze. Re-plumbing took a few hours, not because it was complex but mainly to position the header tank correctly and the make sure the lower radiator pipe was positioned so it didn’t snag the alternator or power steering – tricky.