What are the advantages and disadvantages of using a thicker oil (e.g. 20W50, 15W60, 10W50) in my 2005 RX-8 as compared to using the Mazda rotary 5W30 that I have been using for the past 5 years? I have read it is a good idea to use a thicker oil if you live in a hot climate, and the manual shows this as an acceptable oil. I live in a part of Australia where the temperature range is from 45 degrees at night in winter to 95 degrees in summer during the day, so it never gets anywhere close to freezing and it is quite humid in summer. I assume a Penrite or Castrol product should be fine (e.g. Penrite's website recommends their HPR15 oil which is a 15W60)? Perhaps there is a good and reliable thread on this already that I missed? Thanks.

 

You need to read up on oil viscosity.

http://www.aa1car.com/library/oil_viscosity.htm

Search and read.

I am running Castrol GTX 20W-50 during spring, summer and fall in NYC. Climate temps range anything from 45-105+ degrees Fahrenheit during the time I use 20W50. In the winter when the temps will fall to freezing, I will switch back to either 10W30 or 10W40.

Again, search... These oil discussions have been posted thousands of times.

 

Thanks, good article. I am looking for the pros and cons for a rotary and will search the forum. It seems some articles are saying the risk of using a thicker oil is the ability of the MOP to get the thicker oil into the engine chamber.

 

No worries about it, here's my oil viscosity:

Idemitsu fully syn 5w 40 : 4.5k-10k milleage
Trust F2 fully syn 15w 50 : 20k-45k milleage
Idemitsu fully syn 5w 40 : 45k-50k milleage
Royal Purple syn 10w 30 : 50k-70k milleage
Shell Helix mineral 20w 50 : 70k-95k milleage
Shell Helix mineral 15w 40 : 95k till now 120k milleage

 

Geesh. 20W-50?

 

^ right, but now they change it to 15w 40, so far no prob

 

To each his own I guess.

 

^ +1 to each his own coz mostly the RX8 here used that kind of viscosity

 

I've been using 20W-50 since day 1 coz Mazda gave me a 100k km free servicing. So my car can be a guinea pig that uses the cheapest mineral oil and we'll find out what happens hopefully in a long long time.

 

OP, seeing I guess you are in Australia...I use Castrol GTX 3 a 15W40

 

damn noob !

ever since they replaced my engine, hmm, well for the first 500 miles on it it was using stock 5w20 motorcraft garbage ...

but after that, nothing but 20w50, even Winter, oh yeah.

This winter I might back down a bit on something like 10w40, not because Im afraid of using 20w50, I got some 10w40 for almost free (just paid shipping, lol) so why not ? or maybe I will leave those for my car's CX-7 and my new Mazda3. meh, will see.

 

btw, great article SNTP

the dexos oil part, lol, watch a lot of people gonna messed that up and more warranty denial for GM. and latest spec is SN oil.

 

Yeah man, you've only had what? 3 engines? You're a noob until 5 at least....

 

He's only on his second engine. The first blew despite using synthetic oil.

RXZ08 - your owner's manual shows a bunch of grades. It shows that you should use something thick in hot climates. As long as you use something on the chart that fits your local temperatures, you're fine. Conventional wisdom with most cars is, given a choice, tend to the thicker rather than thinner.

Ken

 

Hmm, I am tempted to stick with 20w50 for this winter rather than buy 10w40. I still have 6 quarts left from my 12 quart box I got from the Zzzzone.

 

Think about it. How many hours of driving does it take you to run through 1 quart of oil? 20 hours or more, most likely. You could run Molasses, and the OMP would still be able to push a quart of it through the 4 holes in 20 hours.

 

I was waiting for the heavy oil king to chime in,

I need to do freeze test with 20W50 and see how it turns out. I did it with 0W40 and the pour test was interesting to say the least and that was only at 30F or so.

 

My freeze test was pretty ghetto

I just left a bottle of 20w50 rp out when it was like 25 outside. Its thicker for sure, but nothing ridiculous

 

First one failed the 2nd compression test. First test was actually still ok. what happened during thise 9months to the engine? I have no idea. Hell the engine might be bad to begin with. Who knows

 

Hmmmmm you have a point.

Damn. Now I gotta wait a lonnggggg while to get rid of the noob status...

 

Looks like im going to throw a bottle of Castrol GTX 20w50 into the freezer right now. I think I have two or three quarts of GTX 10W30 in the basement too. Ill throw that in there with it. The 10w30 is at least 10 years old though

 

I think I have a bottle of 0W40 in the garage, I'll freeze that and some 10W30 Castrol and compare.

 

Report back with reactions of housemates (girlfriend, wife, mom, dad, roommate, buttbuddy, etc) when they open the freezer.

 

Reporting back after the ghetto test. My freezer is about 12 degrees Fahrenheit, I chucked a bottle of 20W50 in there and freezed it over night. I took it out and tried shaking it to see how thick it is (I used about a fifth of the quarter already). It didnt slosh inside. I ran out and tried pouring it into the filler hole. At first a chunk of what seems to be sludge came out, but the rest poured in at a fairly slow rate.

I know this isnt an accurate test to see if 20w50 is safe in an RX8 during times where it sits below freezer temps for a long period of time. After seeing how thick 20W50 may get in low teens temp, I am a bit iffy about using it when it is below freezing. I am sure after the engine runs for a minute, the oil temperature will be high enough for the oil to become thin. What scares me is during that minute of warm up with thick oil.

 

^ yep. And what brand was it?