Lead additive question

[clavilux]

Hey, I've seen various discussions on this, most ending that it's nothing more than snake oil and by the time any valve damage occurs, the engine is in need of a rebuild anyway for reaching such high mileage

For the price of it, I think, for peace if mind it can do no harm... or can it?

[bricol]

I've been using a Texaco additive I bought in bulk a long time ago in my crossflow powered trials car - spends a lot of time idling on car trails, interspersed with lots of revs when on sections, and lots of sustained high revs on road sections on classic trials.

Without taking the head off, I can't tell if any damage is occurring, but in the tappets haven't needed adjusting to regain clearance in 20 yrs, so the valves can't be hammering too far into the head.

[ferny]

Some brands are curse word. I used to use Castrol as it was regarded as one of the best, but then didn't bother.

If your engine was designed to be used in America (certainly California) there's a good chance it won't be needed. Their emission restrictions were much firmer before ours and engines were built to suit. There's also a theory of lead memory, where lead deposits embedded in the head negate the need for it. That would probably be a myth in my head. Another theory is that the metal has become hardened through heat cycles and constant tapping from use and is now already hard.

I've had valve seat recession on unleaded engines, converted engines and non-unlead engines. I used to drive them very hard and I also think luck plays a role.

Would I buy and use it now? Not on an old engine. But I'd keep an extra eye on the the adjustments and check more frequently than really needed.

[theoldman]

What car, what year?
I had a 1967 Jaguar 420. 'Early' 1967 didn't have hardened exhaust valves and seat inserts, 'late' '67 did. But Jaguar didn't keep accurate enough records to be sure which engine numbers had which setup!

The 'Lead Memory' effect is real, but it 'wears off' especially when run at high loads/high speeds for extended periods.

The additives from reputable brands do work but are nowhere near as effective as lead and even more susceptible to high load/high speed.

If the car is a summer use back and forth to shows and the occasional Sunday Pub lunch run I use the additive - when I remember. When it needs its next top-end overhaul it will get exhaust valve seat inserts and new valves.

If you are talking about a Blower Bentley, Type 35 Bugatti or an Alldays and Onions......................