Rx4000h

[graywolf]

Sorry but here is another nube question. Do I really need to use premium gas in my 2006 RX440h? I asked my service adviser and got a long story that meant yes use premium. I need to know what owners think.

Thanks

[Kyle Petree]

Woah, your kinda flip flopping there with your typos, first you have a 4000h then a 440h...

Anyway, no you do not need to use premium fuel, however you might get better performance if you do.

[RX400h]

The 2006 owner's manual does state that regular is acceptable. I use regular during cooler months and switch to midgrade when the weather warms up. My guess is that an Rx400h using regular fuel when the ambient temperature is 50 is just as powerful as the RX using premium when ambient temp is 80. Since it rarely exceeds 80 here in San Diego, midgrade works well for my RX.

[graywolf]

Woah, your kinda flip flopping there with your typos, first you have a 4000h then a 440h...

Anyway, no you do not need to use premium fuel, however you might get better performance if you do.

Thanks, no excuse for the typos. I could say the cat was helping me.

[graywolf]

The 2006 owner's manual does state that regular is acceptable. I use regular during cooler months and switch to midgrade when the weather warms up. My guess is that an Rx400h using regular fuel when the ambient temperture is 50 is just as powerful as the RX using premium when ambient temp is 80. Since it rarely exceeds 80 here in San Diego, midgrade works well for my RX.

Thanks, I appreciate the information.

[wildta]

The 2006 owner's manual does state that regular is acceptable. I use regular during cooler months and switch to midgrade when the weather warms up. My guess is that an Rx400h using regular fuel when the ambient temperature is 50 is just as powerful as the RX using premium when ambient temp is 80. Since it rarely exceeds 80 here in San Diego, midgrade works well for my RX.

I live in SD too. Do you use mid-grade during summer months but never premium? I've been using premium but started doing research into the octane thing, and thought I might be wasting money buying premium. Have you done any testing using regular for a while and then switching to premium? Just wondering if you noticed any performance or mpg difference btwn the two.

[RX400h]

The 2006 owner's manual does state that regular is acceptable. I use regular during cooler months and switch to midgrade when the weather warms up. My guess is that an Rx400h using regular fuel when the ambient temperature is 50 is just as powerful as the RX using premium when ambient temp is 80. Since it rarely exceeds 80 here in San Diego, midgrade works well for my RX.

I live in SD too. Do you use mid-grade during summer months but never premium? I've been using premium but started doing research into the octane thing, and thought I might be wasting money buying premium. Have you done any testing using regular for a while and then switching to premium? Just wondering if you noticed any performance or mpg difference btwn the two.

I believe that the weather here is cool enough so that premium is not necessary, so I haven't used that grade of gas, at all. Keep in mind that any difference in power would be difficult to feel under normal driving conditions. This is why Consumer Reports editors advise readers who drive cars that can use any grade (because of knock sensors and computer-controlled timing and fuel trim capabilities) of gas that buying premium is essentially a waste of money if moderate driving is the norm.

However, a trip to Las Vegas during August would warrant filling the tank with premium.

Using midgrade, there is more than adequate power for the type of driving that my wife and I do.

[Gryphon]

I did a 20,000 oil change last week and also began an experiment for 5000 miles using regular fuel instead of premium. Still Costco fuel FYI.

It is also summer in Arizona, meaning quite hot in the desert.

I will report later on my findings and changes if any in fuel economy, performance, etc.

Tom

[BadBrad]

Have always and only used regular for 34000 miles. Rather than use premium, just send me the extra money.

[RX400h]

I did a 20,000 oil change last week and also began an experiment for 5000 miles using regular fuel instead of premium. Still Costco fuel FYI.

It is also summer in Arizona, meaning quite hot in the desert.

I will report later on my findings and changes if any in fuel economy, performance, etc.

Tom

I guarantee that in 100-degree heat, using regular gas will result in a big chunk of power drop, but if you modify your driving habits to compensate, you may not notice a decrease in mileage. (At least that's my assumption.)

[LexRexBlue]

We keep tossing this gas question around. I have used regular for almost 4 years. Recently my mileage has been down despite ideal spring weather for mpg. It was suggested that maybe there were too many deposits and I should try 2 tanks of premium to see if it cleared up the problem. Well, my mileage was down. As the price differential is about 38cents a gallon the other day I filled it with regular. Surprise! My gas mileage went up! Now, is it because the "junk" was cleared out, does my car just love regular? Is it because Shell has added nitrogen??? Who knows. Time will tell.

[wildta]

I did a test for the 14k miles. Here's what I got driving around in SD in my 2008 RX400h.

ACT MPG is actual calculations based on odometer and gas receipts

DIFF is the difference I got from actual calculations versus the on-board computer

MILES amount driven using a specific brand/octane

OCTANE type of gas

ACT MPG DIFF MILES OCTANE BRAND DATE

23.18 0.44 3924 Prem Varied 2/21-6/23

22.11 0.70 5033 Reg Varied 7/6-11/20

22.84 1.07 4550 Prem Varied 12/4-4/19

(re-sorted data by brand/octane)

23.37 0.43 2596 Prem Chevron Varied

21.95 1.27 1948 Reg Chevron Varied

22.73 1.03 5543 Prem Shell Varied

22.21 0.35 3085 Reg Shell Varied

24.45 -0.65 335 Prem Valero 6/3

Attached as image too since pasting the excel chart looks funky on here.

So there's definitely not a significant difference in MPG that would warrant the extra cost in premium. However, I did notice a difference in power whenever I switched over octanes which is important to me since my driving style is heavily geared towards the lead foot type. I am now going back to Regular for my next 5000 miles (I basically switched in btwn oil changes). I typically used the same gas stations and pump as much as I could, but just for show I also broke it down by brand. In case you're wondering, I guesstimate about 75% of my time is spent on highway and not so much of the stop-and-go kind during rush hour since I try very hard to avoid those times.

MPG Chart.bmp

[cduluk]

nice results!

[BobBass]

Wildta,

Glad to see your "real world" gas mileage is similar to what I get. I keep reading about these people claiming 26+ mpg and wonder how they're achieving it. They must barely push the accelerator and never go above 55 mph.

I'm from SE PA where we have 10% ethanol gas and have used regular since leasing the RX in 11/07. With mixed driving, in the winter I'm lucky to get 22 mpg and today the readout showed 25.1. I'm not about to spend the extra $ for premium especially after reading your post.

[cduluk]

The manual for the Rx400h states that regular fuel "can" be used, but suggests you use premium. Not really sure why, whether it be for increased fuel mileage or for engine longevity.

Since I plan on keeping this car for a LONG time I'll keep using premium fuel. The extra cost vs regular is quite large, but I guess it's better than having to replace costly car components further down the line...

And I do notice an increase in power with premium fuel vs regular, but still not worth the difference in price...

[katzjamr]

i have used both and prefer the power of premium, also in one of the hundreds of posts on this subject we had an engineer post here that our rx engine was designed for premium, he said it much better than i can paraphrase, will try to find the post. i know the engine can adjust to different octane ratings, the midgrade soulution sounds interesting.

[RX400h]

I'm not sure why many RX owners ignore mid-grade. I use it for most of the year and find it to be a good compromise between power and cost.

Of course, if I lived in Arizona, I'd be using only premium during those super-hot seasons.

[2007 Rx 400h]

I use only BP Premium (93) gas or very rarely Shell Premium, thats it. Nothing else. initially i tried to see the difference using regular and the mid-grade fuel (91), the difference i have been able to notice is the car seems smoother and give a better mpg when using the premium plus and as recommended by auto experts, Premium is good for the engine's long life...

[RX400h]

Remember, using premium fuel during cold Winter months is somewhat akin to using 98 octane fuel during Summer - not necessary, since the colder, more dense air during Winter allows the use of lower octane fuels without suffering any ill effects.

Similarly, you should wear sunscreen if working outdoors in Hawaii but stop buying it if you move to England; it's not necessary!

[2007 Rx 400h]

Now that the summer season has kicked in, i will continue to use premium (93) grade and by the end of fall season, i will experiment with 91 grade!