Thread: TD5 Oil Report.

I plugged it into chat gpt.

I learned that the TD5 injectors put high shear load on the oil. There you go...

Good — I’ve read your full oil analysis report. Here’s what “viscosity low for specified oil grade” means in your case, and what to do about it:

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? Summary of your report

• Oil: Valvoline SynPower 5W-40
  
• Time on oil: 5,350 km
  
• Viscosity @ 40 °C: 66 cSt (a bit thin — normal 5W-40 should be roughly 80–90 cSt)
  
• Viscosity @ 100 °C: 11.8 cSt (slightly below typical 12.5–14 cSt for a 40-grade)
  
• Fuel dilution: 1 % — small, but enough to lower viscosity a little.
  
• Wear metals: all normal.
  
• Soot, water, glycol: all excellent.
  
• TBN (8.5): healthy, oil still has plenty of life.

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⚙️ What “viscosity low” means

Viscosity is how thick or resistant to flow the oil is.
Your oil has thinned slightly compared with a fresh 5W-40, so at engine temperature it behaves closer to a high-30-grade oil than a true 40-grade.
That can happen because of:

1. Fuel dilution — a small amount of diesel mixing into the oil (your 1 % reading would cause a few cSt drop).
   
2. Shear — mechanical breakdown of the oil’s viscosity improvers in the TD5’s high-shear unit injectors.
   
3. Natural thinning from long hot running, though at 5,000 km that’s mild.

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? What it means for your Defender TD5

• A small drop like this isn’t harmful, especially since wear metals are very low.
  
• The TD5’s unit-injector system is known to shear oil more than average, so some viscosity loss is typical.
  
• You might see this more if you do a lot of short trips or idling (fuel dilution).

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✅ Recommended action

• Keep using the 5,000–6,000 km change interval you’re already doing — that’s excellent for a TD5.
  
• Use a robust synthetic 5W-40 (like Valvoline SynPower, Penrite Enviro+ 5W-40, or Castrol Edge 5W-40 A3/B4).
  
• If you prefer, you could try a slightly heavier option (e.g. 5W-50) in warmer weather or long-distance towing, which will resist shear a bit better.
  
• Re-sample next change, as the report suggests — it’ll confirm whether this was a one-off or a pattern.

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Would you like me to show what the expected viscosity ranges are for 5W-40 oil (fresh vs used), so you can compare your numbers directly?

One of the reasons why a semi-sun like HPR Diesel 5 is a far better performing oil in the TD5 engine.

Interesting recommendations. I've always run 5-50 Mobil 1 which is within the TD5s expected viscosity range and normally change oil mid service. Apart from when there is engine damage, there is still absolutely zero blow by at 318,000km.

Originally Posted by Slunnie

Interesting recommendations. I've always run 5-50 Mobil 1 which is within the TD5s expected viscosity range and normally change oil mid service. Apart from when there is engine damage, there is still absolutely zero blow by at 318,000km.

I used to run Mobil Delvac 1. I think it was great oil - but I gave up on it because it was too hard to get retail. The specialist I go to uses 5w-30 FE synpower because it's supposed to be specifically for LR and works in the newer LR, but I'm glad I insisted on 5w-40.

I if you follow chat GPT through ... "can you recommend a good 5w-50 for me". It recommends Mobil 1™ 5W-50 FS X2 as the top pick.

There aren't many good 50 oils these days. When I've used up the synpower 5w-40 I will switch to the Mobil 1.

Lessons from this. 15k for my usage is unrealistic. I'll stick to changing every trip.

Oil samples are cheap. I'll keep doing them.

Originally Posted by Captain_Rightfoot

I used to run Mobil Delvac 1. I think it was great oil - but I gave up on it because it was too hard to get retail. The specialist I go to uses 5w-30 FE synpower because it's supposed to be specifically for LR and works in the newer LR, but I'm glad I insisted on 5w-40.

I if you follow chat GPT through ... "can you recommend a good 5w-50 for me". It recommends Mobil 1™ 5W-50 FS X2 as the top pick.

There aren't many good 50 oils these days. When I've used up the synpower 5w-40 I will switch to the Mobil 1.

Lessons from this. 15k for my usage is unrealistic. I'll stick to changing every trip.

Oil samples are cheap. I'll keep doing them.

Thats interesting, the oil chat GPT has recommended is the exact oil that I use. Every many and his dog uses Penrite, but I really have not been able to ever fault the Mobil 1 5-50 and still cant. Even after the sump filled with diesel after cracking a head (2 actually), there was no blow by. As in you could put a piece of paper over the filler hole and it just stayed there. The dealer when it was new used to use Mobil 1 0-40 I think it was.

I've always thought that good oil and regular or mid interval oil changes are never a false economy.

Originally Posted by Slunnie

Thats interesting, the oil chat GPT has recommended is the exact oil that I use. Every many and his dog uses Penrite, but I really have not been able to ever fault the Mobil 1 5-50 and still cant. Even after the sump filled with diesel after cracking a head (2 actually), there was no blow by. As in you could put a piece of paper over the filler hole and it just stayed there. The dealer when it was new used to use Mobil 1 0-40 I think it was.

I've always thought that good oil and regular or mid interval oil changes are never a false economy.

When I was buying delvac 1 it got to the point where it was a depot only thing and in 20l. It was just a PITA to get. I remember the specialist when they replaced the ECU loom at maybe 80k? saying we're worried your engine is leaking diesel into the sump. We've never seen a TD5 so clean. (it turns out it wasn't leaking!)

And then I just got lazy and let the specialist do it. Actually I looked back through the receipts.. up to 2015 they were using the same oil I'm using now... Valvoline 5w/40 synpower and the next receipt in 2016 had the 5w/30. They must have changed everything over to the thinner stuff for the newer cars. I'm on it now though.

Luckily my car has never every gotten anywhere close to the 15k interval - about 5 is all it's ever done. I'm sure changing often is the best thing you can do.

There are several recorded cases of increased lobe wear running the Mobil 1 oil in a Td5.

Justin will confirm

Originally Posted by Tombie

There are several recorded cases of increased lobe wear running the Mobil 1 oil in a Td5.

Justin will confirm

Very interesting! I plugged that into chat gpt (doh) and it said that yes it was a thing. It also said that the reports seem to be more about mobil 1 0w-30 rather than the thicker grade. It does make me a little concerned about the 5w-30 the specialist was using, although the oil they were using was synpower FE which is land rover approved so you'd think it would be ok. I guess nothing I can do about that.

I'm very keen to hear confirmed reports though.

I also asked it to recommend an oil, and mobil FSX2 5w-50 was it's top pick. There was also a liqui molly, nulon, redline oils. Having said that the choices at 5w-50 are pretty slim. It's got to be easy to get.

The oil I'm running now Valvoline 5w-40 Synpower exceeds the LR specs and wear metals are low. Cross fingers as I've probably got 2 or 3 changes worth in stock as I bought up on a super special.