On Sunday, 1 July 2018 06:54:42 UTC+1, Rod Speed wrote:
tabbypurr wrote in message
...
On Saturday, 30 June 2018 16:50:17 UTC+1, newshound wrote:
On 30/06/2018 12:39, Dave Plowman (News) wrote:



400 miles a litre is *not* a badly worn engine. Even more so if it runs
OK. Could be something as simple as valve stem seals failed. And using
a
much thicker oil in an attempt to reduce costs may just result in the
engine really wearing out faster.

does it?

Yep, because the parts of the engine which hasnt got the
problem with ****ed valve seals wont get lubricated as well.

does oil flow reduce if thicker? Or does the oil pump just deliver higher pressure? If it's an engine driven gear type I'd expect the latter.


As you almost suggest, the devil is in the detail.

This is what tabby said earlier

"20/50 is thicker, changing to that *can* reduce consumption. It's a
common tweak on a worn engine, the cost is a fraction more friction, but
not enough to notice any difference at idle on an open loop controlled
engine.

A litre per 400 miles isn't good, you *may* want to consider the other
dodge of adding a tin or 2 of that treacley oil to the engine oil.
Really reduces oil burn"

and he's right, that was one of the traditional routes from the days
where bore and ring wear, or valve stem wear, resulted in significant
"burn"

As you say, it *could* be failed valve stem seals. No such thing in the
old days, but I've never seen a comparison of how much of the historical
improvement in consumption comes from the introduction of seals, and how
much from improved materials and engineering of piston rings and bores,
plus better anti-wear oil additives.

My academic friends in places like Leicester and Warwick reckoned that
one of the big steps forward was the introduction of plateau honing for
bores. You arrange for the first machining to introduce deep scores (and
high peaks), then you remove the peaks by honing to provide the running
surface for the rings, while the scores provide an oil reservoir which
gets replenished from below. It's certainly remarkable how you no longer
have to "run in" a new engine, or pistons following a rebore like we all
did when I first started rebuilding engines in the 1960's.

As you say we can't know from here what the cause is.

But that level of oil use without smoky exhaust can only be due to one
problem.

I remember one where consumption was traced
to oil being dumped on the exhaust manifold.

But that produces a smoky exhaust, which he doesnt have.

it didn't. Nor did it produce any noticeable oil on the ground, that's why it was slow to get diagnosed. Presumably oil only got dumped on the ground on a long bend at speed.


NT