Well we’re not taking the Rover to the family Christmas this year. 🙄

First a little background: I’m the 3rd owner of this 150k ‘91 Range Rover Classic. It’s been meticulously maintained it’s whole life and came with every record since new...Oil changes at every 3k-5k miles along with all it’s other required services done along the way. I bought it about a month ago and drove it from San Diego to Portland with no issues outside of a blown rear defrost fuse and a broken coolant sensor wire. It does have the typical oil leaks, not a lot but a little seepage around the oil pan.

Now to the issue at hand. While doing my pre-trip check over I realized I was almost two quarts low on oil (total fail on my part). There were no previous symptoms, no knocking, no ticking, no rough running. I added two quarts of Castrol GTX 20w-50 (left from the previous owner), let it warm up, checked the dipstick and the level was just below the high line. We loaded up and once it was up to operating temp we started to drive off, there was a little hesitation and what sounded like a couple of knocks or maybe misfires. I figured it was a poorly connected plug wire as I had just changed them. I pulled the wires, reconnected and decided to start off again...same issue. This time I left it running and popped the hood. The knocking sound wasn’t coming from the top of the engine, so I crawled under and observed it seemed to be coming from the oil pan area. It does not change when I put it in gear but does seem to speed up when I give it a little gas.

The only things that have been done in the past week have been plugs and wires, a fresh tank of fuel with some Lucas Injector cleaner/fuel conditioner and then adding that 20w-50. Thoughts? Is the 20w-50 too heavy, it is in the 30s/40s here now so I know that’s a pretty heavy oil...

 

That is probably a bit on the thick side for those temps,

 

 

I don't know that it would cause knocking.

I've seen more than a few times a knock turn out to be an exhaust leak on one side. People have thought it was all manner if horrible failure, rod bearings main bearings slipped liner only to find it was $5 exhaust gasket issue or a cracked manifold

 

 

Its not I've only managed to kill one and that was 190k miles and way to many RPM for a 1000 miles. It just wiped out the valves on one bank. The 3.9 with basic maintenance is pretty damn robust.

 

I'd honestly hook up a mechanical oil pressure gauge on it. That will answer a lot of speculation.

I'd use Rotella 15/ 40 diesel oil I use it year round. Not sure how cold it gets up there. Maybe 5/40 if it gets cold. You may be experiencing oil starvation due to the thick oil.

 

IMHO, now a 20W50 in The PNW is too thick. I'd run a Castrol GTX 10W40 or 15W40 all day and make that 3.9 very happy.

+1 on testing with an oil pressure gauge. And if you are going to drop the oil pan to have a look REMEMBER to remove and clean the Oil Pickup Tube and Screen.

 

PROBLEM DIAGNOSED:

After much un-needed stressing over the long Christmas weekend and just a few minutes of reading through the service records + some actually diag under the RRC. I've come to the conclusion it's a rattling cat with some damn good rhythm haha. Long story short, I found an invoice and inspection form from about 20k miles ago showing that the previous owner had complained about a knocking or rattle coming from the lower part of the engine. The shop noted that it was most likely the cat and it seemed to be intermittent.

I really appreciate the feedback you all gave regarding what the problem(s) may be! With that solved now is what to do next... Should I just get rid of the cats all together? The O2 sensors are in front so I shouldn't have any issues outside of a little extra engine sound or would there be a possible back pressure problem? It's considered a historically exempt vehicle where I live so I don't need to worry about DEQ.

Happy Holidays and Happy Roving