5w20 vs 5w30 - Page 2 - RX8Club.com

Series I Tech Garage The place to discuss anything technical about the RX-8 that doesn't fit into any of the categories below.

5w20 vs 5w30

Old 01-10-2019, 12:35 PM
New Member
Join Date: Jan 2019
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Use 5w-20

USA: 5w-20
HOT CLIMATES: 5w-30 (74F +)

If the oil grade is too thick it won't lubricate the contact between the APPEX seal and rotor housing.

Misconception: there's a misconception going around that thicker oil = more protection. This is FALSE. Stop putting heavy V6 & V8(XW-40+) oil on a freaking 1.3L tighlty compact engine. Trust me I followed this fad and that's how my first RX8 went to ****.

By the way: if you use THICK grade oil it will wear out your seals faster on COLD-STARTUPS. Trust me just use 5w-20 and pre-mix if your going to rip it in the Northeast states. It's how I maintain my RX8 as a daily driver and it fixed a bunch of my problems.

Tips: 5w-30 is a big difference from 5w-20 on rotary engines. We're talking really tightly compact engines. If the oil is too thick it's flow rate may be slower.

If your car is smoking blue on cold startups for a really long time MY POINT EXACTLY

EDIT: If your claim is to use heavier oil as a method to maintain cool temperature on the engine. You suck.. Get a better radiator, better oil coolers or an early fan trigger. If you go with a cheap option such as just using thicker oil you are going to get CHEAP results.

ALSO ALSO: I noticed from running several test that thicker grade oil has raised the engine load % on my engine.

Last edited by Eros Nunez; 01-10-2019 at 12:56 PM.
Eros Nunez is offline  
Old 01-10-2019, 12:40 PM
^^^ Fluent in snark.
NotAPreppie's Avatar
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,124
Thanked 394 Times in 321 Posts
Lets see your data to support the claim that 5w-30 won't adequately lube the apex seals.
NotAPreppie is offline  
Old 01-10-2019, 12:51 PM
New Member
Join Date: Jan 2019
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by NotAPreppie View Post
Lets see your data to support the claim that 5w-30 won't adequately lube the apex seals.
5w-30 is perfectly healthy for summer drives but it will wear out your engine in the winter (40 and below)

My personal recommendation is:
Track: 5w-30(temps must be 65F+)
Winter/spring: 5w-20 + pre-mix if your ripping it.

Anything heavier than 5w-30 will cause friction between the seals. You must remember the space between the housing and the seals is VERY small. Thicker grade oil will just get dragged by the seals and not flow in between the seals and the housing. Which is what we want.
Eros Nunez is offline  
Old 01-10-2019, 01:54 PM
UnknownJinX's Avatar
Join Date: Apr 2017
Location: Victoria, BC
Posts: 2,005
Thanked 282 Times in 260 Posts
Aside from reviving an 11-year-old thread...

I do agree that 5W-20 is adequate for cooler climates. This is what I use for spirited DD and occasional AutoX.

But some people have used XW-40 without issues, and in fact, I would use it if my car sees track time. You need that thicker oil for tracking where your RPM, load and temperature will be so high the thinner 20 oil will break down.

See the UOA thread if you want data.
UnknownJinX is online now  
Old 01-10-2019, 06:58 PM
Join Date: May 2017
Posts: 27
Thanks: 0
Thanked 3 Times in 3 Posts
Ive been using pennzoil yellow bottle @ 10w40 as per the recommendation of several Rotary engine builders. Im in FL so weather is typically near HELL conditions but right now it does dip into the 30s-40sF in the AM startup. I wanted to switch to something thinner for winter temps but honestly... the pour point of the 10w40 is freakin -38F!!!! As per the data sheet. I dont think flow is an issue @ 40F in the morning. Lol.

I run the car HARD daily as soon as it warms up.
Fijibluefg2 is offline  
Related Topics
Thread Starter
Last Post
Billy Marcial
RX-8's For Sale/Wanted
03-01-2018 06:50 AM
RX-8 Discussion
06-27-2006 09:52 PM
Series I Tech Garage
09-17-2004 04:32 PM
RX-8 Discussion
02-23-2004 11:55 PM
Far East/Asia
07-21-2003 05:47 PM

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.

Quick Reply: 5w20 vs 5w30

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.