If you haven't done it yet, and it is your HLA's (hydraulic lash adjuster), try switching to Mobil1 synthetic oil. Many people have had very good luck when switching to this oil is quietening the noise down or rendering it non-existent.
From Julian's site:
Some HLA noise during cold engine startup is quite normal. During shutdown, the 24HLAs are in varying degrees of compression
depending on where the 4 cams stopped at shutdown. Those HLAs experiencing the greatest compression from the cam-lobe
(against a 175lb/in spring) will take longer to pump up at a cold-start compared to their less compressed counterparts. This HLA
pump up time is further compounded by the time elapsed between starts, and to a lesser extent dependent on where the HLAs is on
the oil path - HLAs at the top left of the rear bank (cyl #1) taking slightly longer.
The actual mechanism of the noise from HLAs is a function of the degree of lash between the cam lobe and HLA surface: when
HLAs are pumped up with clean oil & operating correctly they maintain this lash at zero for all rpm (and thus achieving the
self-adjusting maintenance-free operation of HLAs). Some HLA noise is not from the HLAs but from a friction-gear used to reduced
backlash noise from the two cam-drive helical cut gears on the camshafts - for aesthetic noise reasons. Oil cleanliness has a direct
bearing on HLA & Friction-Gear noise incidentally, as well as the acoustics of reflection of noise from the oil-pan oil surface, hence
after an oil change an engine may be noticeably quieter.
Mobil Delvac1 5w40 has much stronger detergents, water absorption (TBN) and anti-wear package than Mobil1, which is of particular
interest to noisy HLAs. It is the best engine oil made, suitable for diesel & gasoline engines, meeting API SJ, ACEA B3 and
Japanese valve-train tests, as well as extended-drain requirements. Delvac1 is US-only, and has helped marginal US 944 & M3
HLAs. However, European Delvac1-SHC is not suitable for petrol engines however.
Best oil: Mobil-Delvac1 (US only). Equivalent: Mobil1, Redline (not race oil as lacks detergents), Comma Full-Synthetic 5wNN (UK),
Amsoil-2000, Valvoline Synpower. Best weight is 5wNN. Mobil1-Delvac1 has higher Ash figures than Mobil1 and is really only useful
for it's higher anti-wear, longer drain intervals and stronger detergents for cars with continuous HLA noise (which is alleviated by oil
Not a Synthetic PAO/Ester based oil, it is a Group-III mineral oil "chemically pseudo-synthetised" hydrocracking to convert wax
impurities (very undesired re sludge) into longer-chained oils without loss of volume thereby maximising profit per raw barrel of
material. Owners of Audi, BMW, Porsche & Mazdas have reported black gloops of wax deposits coming out during oil drains which
are not good for drain-pan screens or HLAs. Ash content is 1.2%, higher than any of the PAO/Ester based synthetics (<0.5%) and
higher even than plain Castrol GTX at 0.7%. Ash forms deposits on valves and sludge, as HLAs will indicate. There are better oils on
the market than this, for the same price or cheaper. Unfortunately Mobil taking Castrol to an advertising tribunal merely had the
effect of allowing just about anything to be classed as "synthetic" when it's not a Group-IV/V PAO/Ester base.
93 Probe GT MTX
Mobil Delvac1, NGK plugs/wires
Powerslot rotors, Axxiss metal master pads, goodridge SS brake lines
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