I've read numerous threads here about the X308s and older models using Rotella or some other brand of 15w40 oil, so long as its specified for gas engines as well as diesel. But there's no mention of anyone trying it on X350s. My car is approaching 140k miles, and I'm wondering if it would benefit from a higher weight oil. I'm currently using 10w30. Any thoughts?

 

There'd be no benefit from a heavier weight oil (possible some disadvantages) and no need for 'diesel' oil either. The higher levels of ZDDP found in the CJ4 oils are primarily of benefit to 'old school' flat tappet and rocker engines.

 

Hi XJ8JR,

My understanding is that newer engines are specifically designed to use thinner, slipperier oils for decreased internal resistance, resulting in increased power and economy. The clearances of bearings and moving parts, piston rings, oil pump, etc. have all been carefully determined based on a specified oil viscosity. Using a heavier-than specified viscosity will not only increase internal resistances, reducing power and economy and making cold weather starting more difficult, but if the heavier oil does not flow as well between moving parts to keep them properly separated, it could potentially lead to increased wear rather than the reduced wear you might expect.

That's why I'm always careful to follow the manufacturer's recommendations for every car we own. For our '93 XJ40, Jaguar recommends 20W-50 in warm climates, but for our '04 X350 the heaviest recommended oil is 5W-40. According to the X350 owner's manual, the range of recommended viscosities, depending on ambient temperatures ranging from -22F to 120F, is:

0W-30
5W-30 (recommended)
0W-40
5W-40

Cheers,

Don

 

Interesting. Thanks for the input!

 

Hello, well I am a filtration expert so I now a little bit about oil ha. OK, first, the first number is how thick the oil is when cold, and you never need thicker oil at start up. I would never recommend anything over 5w-XX. As Don said, 10w30 oil actually takes longer to get to engine parts when cold because the thick oil is harder for the oil pump to suck it out of the pan and then push that oil thru all the tiny ports. So, many people know what I have just stated above, but what nobody knows about, how about that oil filter? Pour milk thru a coffee filter, it goes right thru correct? OK now lets use something thicker, pour syrup thru that filter and see what happens. You cant get it thru, just like your engine oil filter!!! Luckly there is an oil bypass so you wont starve your engine for oil, but that bypass is exactly what it sounds like, once a specified amount of oil pressure is trying to push oil thru that filter, the bypass is pushed open and now your engine oil is bypassing the oil filter. Obviously you really don't want unfiltered oil oozing thru your engine. And trust me, 15w-40 is as thick as honey at cold temp. Now the cool thing is, the first oil number is followed by a W because it means winter, or cold flow, so if you use 0w-40, the oil is still thin when cold, but is is just as thick as 15w-40 when at operating temps because the 2nd number is the same. Simple, the wider the spread of the number on an oil bottle, the more stable the consistency or thickness is throughout the temperature range. Take a bottle of 0w-40, 5w-30, and 10w-30 and put them your freezer for a few hrs. Now shake them, and you will be alarmed at how thick even 10w-30 is, however the 0w-40 will be almost the same thickness as when you put it in. 0w-40 is THICKER AND THINNER than 10w-30, just depending on the temperature.

And as Mikey said, ZDDP or zinc compound is not needed in modern engines. The zinc compound was removed from gas engine oils to help decrease in gas engine emission. And you might ask how does oil affect emission, well the PCV system sucks the crankcase vapors (oil vapor) back into the intake to burn them thru the engine. Diesel oils still have zddp in them because they have different emission standards. Racing oils have very high levels of zinc in them because it does have superior lubrication properties, but they simply cant put zddp in regular oil thanks to the government crack down on emission. If you are worried about this, you can buy bottles of zddp and add it after an oil change. They only removed the zddp in oil about 4 years ago. I can tell you it DOES make a difference in older engines. We seen several camshaft wear flat after this. We see many older engine at my work all the way back to the 1920s.