So, as many of you know from previous threads my truck runs a bit warm, like 210 on the highway and up to 215-221 around town (never overheats or even gets close, just runs warm). Everything in the cooling system is new and tripled checked, yet I still see those numbers (new radiator, HD fan/clutch, hoses, water pump, belt, t-stat, Peak, water wetter, sensor). Being I've completely exhausted my possibilities of what to look for, I'm going to do what I was doing before I got the gauge... drive the damn thing and not sweat it.
With that said, the one thing I will do is make sure to change out the oil frequently, as well as send the next batch off to Blackstone to be analyzed. I was thinking though if running the turbo diesel rated M1 5W40 could be helpful. I know it won't make it run cooler, but the properties of that oil make it withstand heat better, and also do a better job of keeping things clean under that heat.
Everything I see points me to thinking it would be perfectly fine to run in there, but figured I would poll the audience on thoughts. I know the Shell T6 is "HD" and used in many TD trucks, so likely contains the same additional additives and extra detergents. I'm just a M1 fan though, and if you get the right deal it actually comes out cheaper (sometimes able to get the oil plus an M1 filter for around $35 total).
So again, this is not a debate over oil brands, but rather if the specific TD formula can be run in my feverish Disco. With it help, hurt or do the same as regular oil?

 

Should be a reasonable oil to run.

Have you ever in all this fun changed the engine coolant sensor, which makes those numbers, or compared that reading with an IR thermometer pointed at the outlet pipe from the engine?

I know you have a new radiator, but is water pump original? Spec for a water pump is 2.6 gallons a minute at 1000 rpm, 10 PSI. So a working pump should circulate the entire coolant system in about a minute or less at freeway speed.

IMHO the stat needs additional hole(s) in the sample disc on top. If 221 water was in the stat, it would be wide open. Maybe increased fan flow is cooling off the stat more than the Rover gods planned. Take a drive with fan off (belt on) on highway. Just don't idle at McDonalds too long. Or Duct tape some cardboard around stat to block air, make it warm up more.

 

Yep, water pump was newer before, and put a new one in anyway (I was worried about it since the fan had that wobble). I'm thinking too that maybe it is being overcooled up front and the stat just is not feeling that hottest of the water. I did replace the sensor anyway with again no new results.
The fact is it is cooler than it was before, and I am thinking that since it likes to stay at a few numbers (210, 217, 221 depending on conditions) that the extra cooling up front is quickly knocking temps down to below full stat open. If you remember, I even changed the t-stat out that one extra time to a LR one just to be 100%.
Here is the old water pump... perfectly fine:

 

Maybe the overcooling idea has some merit - hockeymom1 reported like 208 before they changed to in-line. If it is ever at the dealer (bad thought) let them also look to see what region the ECU is set for (don't know if some other region setting, with an NAS engine, would produce higher temps). Hard to tell why your Disco has a temperature and others don't.

IMHO what someone could do is produce a stat housing that bolts where the pipe exits the block, like earlier engines had. But you have three holes, and D1 blocks have two, pretty sure they don't line up.

 

No issues running that oil whatsoever, it meets spark ignition standards as well as compression.

It's a good thought on the region coding but the ECM drives the temp gauge and "decodes" the sensor readings. Unfortunately the ECM isn't regionally coded in the traditional changeable sense. That being said, there are any number of things that could throw off the reading, like dirty or corroded connectors or a slight issue with the algorithm within the ECM.

 

I will give it a go. Especially in the cold it might be better to have 5w vs the 10w40 m1 anyway.

 

On the connector issue, the sensor drops resistance as it heats up. So another "short" (like green corrosion) across both pins or at a header connection, would lower that resistance even more. Whenever two resitances are in parallel the resulting equivalent is always less than either of them individually. I had this on my Merc, my temp gauge kept reading strange until I found the "blob" - changed stats, water pump, etc. Now if goop was on just one conductor, might read colder. A ground (skint wire in harness) would probably read warmer. Could unplug Stat and ECU and meter pins. I know if I unplug my D1's the scanner says -40F, which has not happened in these parts since Al Gore can remember...

 

Although it will work fine, the M1 0W-40 would be a better fit. It really is the gold standard for 40W oils out there. Has a TON of OEM approvals, better cold flow characteristics and has a better additive package.

 

Same song/dance. Stats:

50737 miles
New t-stat/ expansion cap/ Green Peak Anti-freeze with Water Wetter
Warm Idle 208- 217F
City driving 204-210F and creeps up at a light around 210-212F
Rotella T6 with Mobil 301 filter

Twice flushed radiator with Peak Green to make sure all the Dexcool was out. Pressure tested the second time to make sure no leaks and it held.

2x/week I pull the dipstick and check level in expansion tank and for leaks external. I thought I smelled antifreeze coming out through the exhaust but not sure. Definitely keeping an eye on it.

Feels like a waiting game... which is a Pita.

 

That is the only oil I will let touch my Audi, as well as my previous twin turbo Audi. Great stuff. Just thinking with the older Rover that is running hot and may be a bit dirty, the TD formula could be good