Hi all, I have an 03 touring z w/ 118k~ miles. I'm almost due for an oil change this coming weekend and I've been reading the UOA thread posted here. It seems that Mobil 1 0w-40 gave the best results compared to all the others. My question is, is that since Mobil 1 is a synthetic oil and the previous owner has put conventional oil (5w-30) in it for 6 years, is it still fine to switch to synthetic? I've checked the oil change records and it seems that at one point it was on a synthetic blend.

Also, I live in Cali, in the winter temperatures can drop down to around 25f and during the summer around 110f. So would the Mobil 1 0w-40 be good for year round useage?

Thanks all!

edit: What oil are you guys using?

 

Mobil1 0W-40 is fine to use in 25F weather, so is Mobil1 5W-30 since there is no appreciable difference at that temperature range. Now if weather could go down as low as -25F, it would be a different story.

Be aware that UOA results can be interpreted in different ways and the internet is a wonderful place to get misinformation. Switching to synthetic oil should pose no problem, but if I assumed correctly that you didn't expose your car to racing duty, the conventional oil would work just fine.

I have used Mobil1 0W-40 during last winter in which temperature went below zero quite often. I think it wouldn't make much of a difference if the oil used was 5W-30. Currently, my Z runs Mobil1 5W-30 which meets GM Dexos requirements.

 

Yes completely fine.


For the mileage on your vehicle and temps you're describing, 0w-40 will be fine. The first number is what you should be concerned with when factoring in outside temperatures. In layman's terms the first number correlates to the viscosity of the oil upon start up. The lower the number, the thinner the oil will be at start up. The thinner the oil is, the easier it is to quickly distribute throughout the engine. This is crucial upon start up and especially when the temperature drops outside. The 2nd number is the viscosity the oil turns into after it reaches normal operating temperature. It gets thicker.

Read this thread if you want to truly understand it all, I did:

https://my350z.com/forum/engine-and-...-and-info.html


Mobil One 0w-40...

 

I'm another Z owner who uses Mobil 1 0-40W. It actually pours like a 30 wt oil, so it's OK to use during high temperatures. As others have said, switching to a synthetic should be no problem with your VQ.

 

The oil, of course, does not get thicker as it's heated, although that seems to be a common misunderstanding. Ever drain your engine oil and see how it's very much thinner when it's hot (which is why you drain it hot)?

The 2nd number means the 0w/40 oil will have the same viscosity as a straight 40 wt. oil at operating temp.

 

I stand corrected. I was trying to put it in layman's terms. But yes you are correct, it does flow easier when it's at operating temp...

 

Thank you all for the advice! Looks like I'll be picking up some 0w-40 later on this week.
Also, should I be concerned with changes in oil pressure? I always take it easy until the car fully warms up before I do any spirited driving, but because this is thicker oil should I watch out for anything?

Thanks again guys!

 

No. Drain oil, refill with required amount, check dipstick, oil pressure should maintain where it should be...

 

Very impressive collection of oil information. Thanks for the discussion!

 

Got it!

Last question, I actually looked at the oil change records a bit more closely and noticed that it has been running on a high mileage oil for maybe 2-3 years. Is it still safe to switch over? I heard that high mileage oil swells the seals or something.

I was thinking about mixing 4 quarts 0w-40 and 1 quart HM 10w-40 oil to keep the seal conditioners if anything.

Thanks again guys

 

Did the previous owner have slow oil leaking problems or did the engine have a tendency to burn oil between oil changes when the recommended oil weight was used? If you do not know the answer to this, go ahead and run the 0w-40. Check your oil levels periodically. If you're not noticing any oil being burnt and not having to add any, like a quart between changes, then stick with the 0w-40.

In my personal experience I had a 1997 Eclipse. I was the original owner. When I was close to 140k miles, it began burning oil (5w-30). It was burning on average 1 quart between changes. I switched to the heavier oil. It solved the problem...

 

The car doesn't appear to be leaking any oil. The reason why it was put on HM oil in the first place was because the previous owner had his oil changes done at jiffy loop. However if I drive a bit harder than normal I find myself having to add about 400ml every 1k miles. Should I still use the 0w-40?

I'm at the store right now. Is it the one labelled with euro car formula?

 

I have been using 0w40 mobil1 for 8 years with FI and have never had a bad oil report.First with the suck *** stillen s/c and 6 years with the Greddy twins.

 

You would be a fool to run 5w30. M1 0w40 is the better oil for the VQ. There is no reason to ever use an inferior oil like a 5w30, ever.

 

So I did the change yesterday and all seems well. The engine actually sounds a bit quieter and feels smoother too. Let the car sit overnight to check the oil level and it's pretty amazing how thin it feels compared to the 5w-30 that was in it.

Thanks all for your help!

 

You obviously know much more about this topic than the engineers at Nissan. Nice to have you here on the forum.

 

Bold statement to make with no data presented to support it. Especially given the volume of folks running 5w-30 in not just the z but other much higher performing engines.

 

bigsyke means, having an option, why would you run 5w30 vs the 0w40 that has been proven at BITOG to be the more robust oil. Your pretty much good running either, but 0w40 has better wear properties and the additives breakdown slower. Its the rec oil for the GTR because The VR38 engine has plasma-sprayed bores and was developed using this oil, but also the wear was excellent

 

Any oil you use today, as long as it's the recommended viscosity and changed regularly, is going to allow any engine to last well beyond any of us keep vehicles for. If you track I can understand but 98% of the people on this board don't.

 

I switched because according the the oil thread Resolute posted on here, 0w-40 provides better protection for the engine. Also, I checked Mobil 1's FAQ and they say that synthetic doesn't affect the seals.