Ricky C wrote:
I just bought a 1997 Nissan Primera. It has apparently had a boiling
battery at one time, causing the battery acid to spray out. Much the
of the crank case and gearbox has surface corrosion as a reult
(showing up as whitish powdery deposits all over). I don't think this
is a serious problem since it comes off when rubbed with wire wool.
snip
I was thinking of spraying everything under the bonnet with a soda
solution to neutralise any lingering acid that could cause further
corrosion, but someone has suggested to me that soda (or bicarbonate
of soda) will also corode the aluminium engine!

If that's correct. can anyone suggest anopther line of remedial action
to neutralise any remaining acid lingering in the engine compartment?

IMO, it's unlikely that anything is lingering.
But, I'd spray it with a fairly dilute solution of bicarbonate of soda,
say 100g of solid in 5l of hot spray with washing-up liquid.
Leave a couple of hours
Then take the hosepipe (on fine spray) and spray for a couple of minutes.

Bicarbonate of soda will not appreciably degrade aluminium in the short
term.
Soda (lye) is a much, much more aggressive chemical,and may.

The right way of course is to disconnect all the rusted parts, wire brush
them, and repaint.
But this may not be practical.