romin88

Past a few weeks I've been getting a unusual clicking/tapping noise, I think it's from the left side of the engine bay. The sound is not present and I can hear it under very strict circumstances. It might be worth pointing out I've got 160k miles and not sure about the previous maintenance records, I've recently serviced the injectors, changed fuel filter/pump, checked the spark plugs.

* Only on cold start (20c ambient temperature), not present while idling, even tried holding the revs a bit higher in hopes to diagnose it.
* Under load (while driving), 1.5k RPM until 2.5k RPM only, any higher the sound disappears.
* Once the coolant needle goes above 1/4" from down, the sound gets less and eventually disappears within 5 minutes of driving.
* I've tried changing oil viscosity and fuel grades, even different pumps but it makes no difference.

I won't hear it any other time which makes it very tricky to diagnose and the sound is very light clicking noise which increases with revs from 1.5k till 2.5k.

Any help, directions to diagnose would help a lot.

911LE

It sounds like you might have an exhaust leak from either end of the exhaust manifold or possibly a cracked manifold.

LS430inDE.

My LS has a noticeable tapping on a cold startup, but only when in extremely cold weather conditions (to me and the LS). She will tap for a minute or 2 on a cold startup when it's about 20deg F or colder. I noticed you said on cold start 20deg C startups. That's almost 70deg F! By any vehicle/engine standard, 70deg F ambient isn't remotely cold.

I would run a can of engine clean in the oil before your next oil change, and at your next several oil changes. Gunk or Liqui-Moly or whatever your flavor engine cleaner will unquestionably remove accumulated sludge and varnish, from all the lubrication galleries, journals, etc.

Whenever I buy a new-to-me car, I'll always run an engine clean (add to oil) when doing an immediate oil change, after buying the car. There's no telling how frequently the previous owner did or didn't change the oil, and running a can of engine clean with the oil will help de-sludge areas that accumulated. I would follow the instructions of the engine cleaner EXACTLY.

Hopefully you won't loosen SO much sludge that it can't dissolve it all, and the solid particles clog/damage your oil pump, lol. (You might want to do the oil change+flush 2 times, immediately back to back.)

It's an easy and cheap attempt of a solution to resolve your ticking issue.

romin88

I've ordered Mystery Oil and I'll try it that, since I've bought the car I've been doing frequent engine flushes every 4000km with BF EPR, and Liqui Moly Pro Line flush.

romin88

That's what I suspected too, is there any easy ways to diagnose that, I've tried visual inspection but didn't find any noticeable cracks, heat shield rattles or hissing.

LS430inDE.

If it's a manifold issue, the tap should always be there on the vehicle's cold start, irrelevant of the ambient temperature. In other words, on the vehicle's cold start, the noise should be present at 20degF ambient and 80degF ambient.

On your first post you mentioned the noise is apparent on cold startup at 20degC, which is almost 70degF. With that knowledge, I would agree with the hypothesis pointing to an exhaust/manifold issue as opposed to an oil circulation issue.