Oil Preferences and Warm Start Issue
 

Hi guys,

To start, I have a 2008 Nissan 350z NISMO with around 138,000 miles. Everything remains stock other than an upgraded exhaust and coilovers.

My first question and this is one that seems to be asked quite a lot but no recent answers, but what oil is "best" for the HR? I'm not only asking in regards to brand but also weight as I have seen a lot of people recommend 0W-40 quite often when Nissan obviously recommends 5W-30. I personally am using M1 High Mileage 5W-30 at the moment and with my oil change interval coming up shortly I just wanted to ask to see what answers I get that are "up-to-date" if you will as opposed to looking at answers from all the way back to 2010. If it matters, I live in the US Midwest and this vehicle is my daily driver for all seasons, so it does see winter and it also sees summer.

Another question is in regards to a warm start rpm drop that I experience. To be more descriptive, when the vehicle starts up and it is warm, the car will turn over just fine, get to about 1200 rpm, and then immediately drop to around 300-400 rpm before normalizing at around 600-700 rpm. Is this a fairly common issue that I should know the answer to or should I be looking for my own findings? So far I've only changed the air filters with intentions to get to the spark plugs once I can plan out a day to take the car apart and get to those pesky coil packs under the dual throttle bodies. The only check engine light that I have at the moment is an intermittent P0420 or P0430 catalytic efficiency below threshold bank 1/bank 2 that comes and goes.

Thank you very much in advance and I look forward to hearing what you guys have to say.

EDIT: I am aware of the Engine Oil analysis thread. For one, there haven't been updates since 2014 and I don't know if anything has really changed and I couldn't find many answers in regards to the use of 0W-40. Moreover, I quite frankly don't understand some of the lab analyses on there so it doesn't mean a whole lot to me.

The_Laughing_Man suggested an idle relearn. I performed that with no success.

If you keep changing your oil with Mobil 1 5W-30 you'll be golden, there's really not much better you can do as long as you keep up the oil change intervals.

As far as the idle, have you ever touched the throttle bodies? If so you may need to perform a relearn for the electronic throttle bodies to correct the idle.

I have never personally touched my throttle bodies and I doubt the previous owner touched the throttle bodies. Even with that being said, I might do a throttle relearn anyways in case that is my issue. Thank you very much for the recommendation I didn't even think about the throttle bodies possibly being miscalibrated or something of the sort.

I performed an idle relearn to no avail; thank you for recommending it though!

With the codes you're getting have you looked into the O2 sensors being an issue? Assuming the cats themselves are fine.

Also you should definitely change the spark plugs if you haven't done that yet. I see you mentioned getting to the coil packs, old spark plugs can cause idle issues.

I haven't looked into the O2 sensors being an issue, I immediately assumed the cats being an issue because apparently Nissan cats are quite garbage. I took it to my mechanic a while back to get the code checked out with his ridiculously expensive Snap On scanner and he said everything looked solid sensor wise. When I mentioned getting to the coil packs, I was referring to replacing the spark plugs and just that you can't get to the coil backs without removing the throttle bodies and you can't get to the plugs without getting to the coil packs. I do believe the plugs need to be changed so that's what I'm planning on doing once I have the time to take apart my car.

My advice then would be to look into the O2 sensors and/or the cats themselves being faulty, and change the spark plugs. Make sure to clean the MAF sensors and connections when you do it. Also perform the throttle body idle relearn after if you need to. After those things you should either be fixed or well on your way to figuring it out.

Cleaning MAF sensors is a cheap easy troubleshoot as well