What's the most viscous oil that I could use in my 2008 RRS without causing issues?

It's a little bit rattly (tappets?) under load, and a local mechanic suggested an oil change with a thicker, good quality oil might quieting it down successfully. I don't want to break it by filling it with honey, but if safe, I'm happy to try it.

Probably the cam drive chain tensioner needs replacing. Take it to a decent LR indy that knows these vehicles inside out. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

That would be the best solution, however I’m in a fairly remote place with limited regular mechanics, let alone specialists.

At this point I’m keen to try the oil but want to make sure it won’t create more issues...

I would be surprised if anyone here could give you a definite answer to your question. However, using the wrong grade of oil is a well known way to ruin an engine. My guess is that a thicker oil will not do the job if the problem is as RRSTDV8 suggests.

The days of Putting Duckhams 20W 50 in to sort a noisy engine are long gone. You need to find the reason for the noise and fix it.

I'd get the rattle fixed and in no circumstances in any car would I use anything other than the correct specification oil.

RUSK wrote:

What's the most viscous oil that I could use in my 2008 RRS without causing issues?

It's a little bit rattly (tappets?) under load, and a local mechanic suggested an oil change with a thicker, good quality oil might quieting it down successfully. I don't want to break it by filling it with honey, but if safe, I'm happy to try it.