Summer Oil Weight?

The owner's manual says 5W-30 is always fine. It's about 180'F inside the engine no matter how hot it is outside. If the oil isn't too thin at 180'F (when the engine has been running for a few minutes) it's not too thin at 120'F (when the engine has just started on a really hot day).

 

5W-30 is the recommended oil viscosity in North America regardless of ambient temps. A heavier viscosity is not recommended due to potential engine start issues.

Some owners are experimenting with the use of xW-20 oil in an effort to improve mpg. I would not recommend this in your case given the very high summer temps.

Although the engine coolant thermostat strives to maintain a coolant temp of ~185 degrees F (or ~85 degrees C), the surfaces that are lubricated generally operate at much higher temps (i.e., the piston to cylinder interface). As the ambient temp increases, the coolant temp will vary since the thermostat control is not perfect.

One nice thing about Prius is that when you are stuck in traffic the ICE is generally off, hence you don't have to worry about overheating. The AC compressor is driven by an electric motor that is powered by the traction battery via an inverter, so the ICE will come on only when the traction battery SOC drops down to around two red bars.

 

I'm getting ready to do an oil change also, got about 400 more miles to go. I just bought a 5 qt jug of mobil 5w-30 synthetic, you will be fine with 5w-30 in TX.

 

Jeez louise! I would avoid that service writer, and maybe that dealer, like the plague.

 

You will probably get more protection if you switch to a synthetic oil, such as the already mentioned Mobil 1 5W-30. It seems to withstand extreme temperatures better than "normal" oil. It's a lot more expensive, but what the heck, so is gasoline these days.

 

my new accord recommends 5w20, after reading what u guys wrote im kinda worried about doing hard acceleration, I live in south Florida, so it gets pretty hot here.

 

Ford and Honda engines have been using 5W20 oil since ~2000 to help improve mpg. If the engine is speced for that viscosity, then no worries.

 

I'm away until next Wed but thought I'd get caught up on a few things. If you're really worried about the heat, but still want an oil that will offer rapid cold start flow, consider Mobil 1 European Car Formula 0W-40

Mobil 1 0W-40

I currently use this oil in my FJ Cruiser and I have exceptional used oil analysis results. This is considered a "light" 40 oil at operating temps.

In the EU, Toyota allows a wide range of viscosity. Please read the attached Adobe Acrobat file, which has owner manual scans from Spain and Japan. Toyota allows everything from a 0W-20 up to a 20W-50, depending on temps

However, that said, a lot of folks are running even conventional 5W-30 year round in your area with little ill effect. The Prius motor is *not* a hot running motor.

The biggest hot-soak impact on a motor, idling in traffic with Max A/C, does not apply to the Prius. It uses a variable speed electric A/C compressor. That's a lot easier on the motor

 

True enough, outside North America, Honda only recommends a 5W-30 at the lightest oil. However, have you heard of any Honda - or even Ford for that matter - owners having engine problems related to use of a 5W-20 oil?

The best way to determine if an xW-20 oil will work in your application is to do routine used oil analysis. If you start getting a lot of oxidation and nitration, consider switching to a synthetic, or perhaps a somewhat beefier oil.

I run Mobil 1 0W-20 year round in my Prius and it works fine, even with 12 month or 16,000 km oil changes. My FJ motor is a bit different, it seems to prefer Mobil 1 0W-40.

 

But we were writing about a Toyota Prius. You should use whatever Honda advises for the Accord.

 

That looks like a US owners manual in the mid-eighties. Only thing missing is the 20w-20 and the straight 30 weight.

 

Personally I use Castrol Syntec blend because with the way the Prius stops and starts a lot at stoplights, I figure a little synthetic help goes a long way.

And I use 5W-30 myself, which has held up just fine on crazy hot days and long drives.


But then, if there's one thing a Prius engine does well, it's stay cool. You almost don't even need the radiator across most of the US. Just the aluminum block is enough to keep engine temps down. With the radiator added, you could probably drive the thing around on Mercury.

And then, as stated, there's the whole frequent engine shutdown deal.

It's what makes the Prius so hard to keep warm in the winter.

 

I'm a bit leary of using dealership supplied oil during routine 5K mileage services. I heard one too many horror stories on the quality of the oil.
Yesterday, I asked my Toyota service manager what grade oil he recommended and used in servicing the Prius. Despite the 5-30w on the oil cap, he said we put in 0-20w. When I asked why, he explained it was for gas mileage purposes.

ZC1

 

More likely they needed to empty that bulk oil tank next. Be sure to thank him warmly for accelerating the wear in your engine.

 

Actually, in the EU the Prius is run on a wide range of viscosity, from 5W-30 to 20W-50. In Japan, 0W-20 and 5W-20 are approved. See attached

I've been using Mobil 1 0W-20 for a bit over two years now, with an average 12 month or 16,000 km oil change interval. Very good used oil results

 

The likely reason why Toyota specifies 5w-30 in the U.S. Prius, while specifying 5w-20 in other Toyota engines, is that the Prius engines stop very often, stopping the flow of oil across the hot rings and upper connecting rod bearings. The flow of oil carries away heat, so when it stops suddenly so often, a lower viscosity (20) oil may vaporize more than a 30 oil. Using a synthetic ACEA A1/B1 rated 0w-20 or 5w-20 oil would allow you to use a lower-viscosity, higher fuel economy oil, while avoiding hot breakdown when oil is "stranded" near the rings and rod bearings about 500 times a day in a Prius used as a taxi cab, for example. Very few 5w-20 or 0w-20 oils are ACEA A1/B1 rated, a very tough test to pass. In fact, the only one I know of is Mobil 1. Pennzoil Platinum and Castrol Syntec don't pass the test. (The Pennzoil synthetic does meet the older ACEA A1-02 test, an older 2002 test, at least!) It could be that Valvoline synthetic 0w-20 might pass it. I'd go with Mobil 1 Extended Performance 5w-20 year-around, as it meets ACEA A1/B1 and is good for 1-year oil changes. Recommend changing your oil only in the Fall, since their is a natural increase in viscosity as the oil ages a bit, and the last months of the slightly-thicker era of the oil will be in the summer time.

 

The reason for only 5w-30 in the U.S. is simple. The OEM's can use 5w-30 in their EPA test fleets ONLY if they can get the majority of American consumers to use it in their vehicles. The oil used in EPA fuel economy fleets must be "typical" consumer grade oil. Therefore 5w-30 is the only oil listed in the owners manuals now. Also put on fill caps. Europe does not have that constraint. Therefore they still list lots of oils grades that the US used to. By the way it is felt (GM fleet testing, assume Ford and Chrysler to) that 5w-30 will give an average fuel economy improvement of 0.5%. A 1/2 percent is worth killing for. That increase is and was the real driving force to get that oil grade the major one used. Ford did go to 5w-20. My understanding is that it was executive and not based on extensive testing. In GM the only people really in favor to 5w-30 over the traditional 10w-30 were vehicle lines that had 4 cylinder engines that were experiencing winter cold cranking problems. Engine design engineers are basically very conservative when it comes to things that can impact product life. Over time the API 5w-30 has proved itself as adequate.

 

There is little to no difference between a 10W-30 and a 5W-30 at normal operating temperture. In bitter cold conditions, a 10W-30 can even cause engine damage due to lack of or very poor lubrication

You can run something like a 0W-30 and have appropriate year-round lubrication