Michael Hargreave Mawson wrote:
>
> Carly's latest trick is blowing pale blue smoke. :-( I immediately
> started thinking about piston ring replacement, and honing of cylinder
> bores, but my mechanic (bless him) has instead suggested thicker oil!
> For the moment I've stuck in some additive, and will see how we get on,
> but can anyone confirm or debunk the idea that 15W40 is too thin for
> summer driving? The manual seems to suggest that it should be OK,
> but...
There has been some suggestion, on the lists, and in other places
(namely, lubrication-related sites), that thicker oil may actually
exacerbate the problem, rather than cure it.
At any rate, 15W-40, for normal summer temperatures, is quite adequate.
To amplify upon the problem of oil smoke, two things should be checked.
First, in what mode of operation the smoke occurs matters. If it is
present at low engine speeds and large throttle openings, one may
rightly suspect rings. If it occurs at high engine speeds, say, over
4000 rpm, or is more pronounced when closing the throttle quickly at
higher engine speeds, then the likely culprit is large valve
guide-to-valve stem clearance.
In any case, the second thing to be checked, before embarking upon a
bottom-end rebuild, is compression, using dry and wet tests. If the
compression is lower than about 20-25% of normal, the engine probably
needs a rebuild. If the wet test compression readings are 15-20% higher,
or more, than the dry tests, ring replacement is probably in order. If
there's no dramatic difference between the wet and dry tests, but
compression is still on the low side, valve work should be on the
agenda.
Cheers.
--
Michael D. Porter
Roswell, NM (yes, _that_ Roswell)
[mailto:mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`72 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
`80 TR7 (3.8 liter Buick-powered)
`86 Nissan 300ZX (the minimal-maintenance road car)
`68 VW Type II Camper (Lancia twin-cam powered, but feeling its age....)
Remember: Math and alcohol do not mix... do not drink and derive.
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