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RX300: Terrible MPG average related to faulty transmission?

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Old 05-05-14, 09:34 AM   #1
freedannyv
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Default RX300: Terrible MPG average related to faulty transmission?

Hi all,

Firstly, please kindly note that, to my utter embarrassment and shame, I know absolutely NOTHING about cars. I own a 2000 model RX300 and I have a few inquiries I'd like to ask if you'll let me! I bought my used RX only 2 months ago and think I was pretty much 'had' from the off. Since owning it, the Check light has come on and we've had the Knock Sensor and Oxygen Sensor replaced. The Oxygen Sensor took particularly long to replace because it had seemingly gotten so hot it had pretty much welded itself to the car! Finally, the mechanic got it off and changed it. The Check Engine light never went off...

I took the car to a registered Lexus dealer who investigated further into the Check light and up it went on the platform with 3 guys examining my car from all angles. After about 30 minutes they told me the Transmission was faulty and needed replacing. This would set me back several thousand dollars for a new one. I left without getting anything changed.

Now, I drive around town and my average gas mileage is showing up at 11.6mpg! This is 'city' driving. When I took it out on an around the country trip and was mainly on highways, the best mpg I got was around 17. Horrendously low me thinks... I have confessed to knowing nothing about cars, but I do know a thing or 5 about economical driving. As a cheap skate, you naturally pick up these things! I have since taken it to another mechanic who has told me the 'gears' are faulty and offered to replace (I guess the gear box?!) for $800 with a used gearbox. I don't rightly know if this is the same problem the Lexus mechanics discovered, or something else. FYI:

1. My RX is an automatic. When it is in low gear and accelerating, it makes a kind of clicking sound from the front - almost like you can hear it is pulling.

2. I live in Cambodia - it is HOT here. Some days at this time of year are 42 degrees and we have our air con on ALL of the time. This makes me wonder about average MPG - are the people saying that City driving gets you 17-18mpg using air con or not?!

So, to answer my original question, could my terrible MPG average be related to a faulty transmission?

For those who can answer that one question, and anything additional in the way of help you my have, thank you so much. I look forward to hearing some life saving (for my car at least) responses.

Kind regards,

Freedannyv
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Last edited by freedannyv; 05-05-14 at 09:36 AM.. Reason: Forgot the word 'and' somewhere
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Old 05-05-14, 10:54 AM   #2
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If it is not shifting into overdrive you could certainly experience low MPG.
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Old 05-05-14, 11:07 AM   #3
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There may be model differences. Can you confirm that you have and over-drive and it is turned on?
Can you count the gears that your transmission shifts and report?
Also when you are driving on an open road (no longer accelerating .. we call it cruising) at constant speed what rpm and what what speed do the instruments show.

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Old 05-05-14, 11:05 PM   #4
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I can confirm there is O/D and it is always ON.
Counting gears the transmission shifts, meaning how many times I can hear it change? I usually only hear and feel the first gear shift. I haven't listened much for the next changes, but will give it a go if that is what you mean.
I will also try and report my findings while cruising and get back to you!
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Old 05-06-14, 01:31 AM   #5
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You need to get a cheap code reader and see what codes are popping up. Could be something very simple and relatively inexpensive.
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Old 05-06-14, 08:43 AM   #6
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Quote:
Originally Posted by carguy07 View Post
You need to get a cheap code reader and see what codes are popping up. Could be something very simple and relatively inexpensive.
I have done that and nothing comes up any more. We got all of the code readings fixed. My g/f took the car to repair yesterday and informs me the Check light is off... for now. She doesn't know how to explain what the parts were that got fixed. Again, this is Cambodia, so you don't know much about what they do as all receipts are in Cambodian and they barely speak English, if at all.

Still having the problem with the transmission or gears though (please read original post for details), and my question remains - could this effect the average mpg?

We have no idea about how many gears changed. We can't hear it if it does change. The engine sounds fine though - not over revving or anything like that. The revs were just under 2, at 60 km/h. Average mpg still at 11.6
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Old 05-06-14, 09:18 AM   #7
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What do you mean by "Registered lexus dealer"? Is it a shop that advertises they repair Lexus vehicles?

Is there another competent shop you can go to, in order to get another diagnosis? I'm having a hard time believing they correctly diagnosed the "Gears" as failing.
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Old 05-06-14, 03:32 PM   #8
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You might also reset the average mpg readout and start a new measurement after all the work you have done.
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Old 05-06-14, 04:31 PM   #9
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there are alot of factors which may contribute to poor mpg.

What are your driving conditions like? alot of stop and go?
What octane level are you using for fuel in RON or (R+M)2 ?
Do you typically travel with alot of cargo?
Have the spark plugs been serviced?
You may want to get a compression and leakdown test as well. A bad piston ring or bad valve may also cause poor mpg by not taking advantage of the entire combustion cycle.

Last edited by fastnoypi; 05-06-14 at 04:50 PM..
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Old 05-07-14, 01:11 AM   #10
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Can you reset by disconnecting the battery and than check?
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Old 05-09-14, 03:37 AM   #11
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Quote:
Originally Posted by fastnoypi View Post
there are alot of factors which may contribute to poor mpg.

What are your driving conditions like? alot of stop and go?
What octane level are you using for fuel in RON or (R+M)2 ?
Do you typically travel with alot of cargo?
Have the spark plugs been serviced?
You may want to get a compression and leakdown test as well. A bad piston ring or bad valve may also cause poor mpg by not taking advantage of the entire combustion cycle.
Wow, thanks to everyone who is so willing to take their time to help! I'd like to answer all the questions starting with Was the Lexus dealer a registered one? or something to that effect. Yes, I believe they were, but this is Cambodia, and you can never be sure. We took it to another place who said GEARS, but I think they were basically saying the same thing as the Lexus place.

Driving conditions are HOT. Very hot! It's 42 degrees Celsius for half the day (I don't know the Fahrenheit conversion). It IS stop and go, stop and go, and rarely I am reaching more than 30kph / I guess that is about 20mph. Air con is on COLD (lowest temp setting) the whole time. I don't know what octane level is or how to check it...? I don't take anything with me other than my girlfriend and a few empty water bottles we've been procrastinating to clean out Sparks not serviced that I know of. I will look into the other things you have mentioned.

Since buying the car for $13.2k, it really has been nothing but problems and expenses, so I think we are probably going to sell it to a dealership soon and let them fix it. There are also more problems like the radio antenna isn't going back in, like it should and a high pitched squeeling when the car is stationary but in the reverse gear.

Thanks to everyone for your helps! This is a fantastic forum and group of people.

Also, I reset the MPG today, as I often do every week or 2. It was at 11.1mpg before I reset. After, I drove around town for 20 minutes, and checked. It was 9.5mpg. Great huh?
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Old 05-09-14, 06:56 AM   #12
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You definitely have some legit concerns for your mpg since it is roughly half of what is advertised for the 19mpg city.

The very first thing you should try to address is your check engine light, and confirm that your transmission is switching into 3rd and 4th. Do you have the codes available from the reader?

High temps and A/C being on all the time do lend their hand in decreasing mpg, but it shouldn't be as drastic as you are experiencing. I know from experience living in the hot AZ summers where temps are 42-43C.

Other mechanical things that may lend to your bad mpg that i havent mentioned, are clogged air filter,
dragging brake pistons or parking brake on (yes i've seen that on other cars), cooling system damage and a post maf leak.

Cooling system....a pressure test can check if you have any leaks of coolant anywhere . If your cooling system cannot hold pressure, your ecu will compensate to save the engine by injecting more fuel than normal.

Post mass air sensor leak in your intake track can introduce unmeasured air. The calculation that your o2 sensors are making after combustion will tell your ecu to dump more fuel to compensate the lean condition.
Use the correct Lexus/Toyota or Denso OEM replacement for the o2 sensor.

Brakes are easy to check, look to see if the pads are wearing evenly from side to side. If you don't have your brakes bled routinely, a brake piston can hang up. New seals and dustboots are roughly $5-10 a caliper if they need a rebuild, and easy to replace with simple tools.
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Old 05-09-14, 07:41 AM   #13
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Quote:
Originally Posted by freedannyv View Post
Wow, thanks to everyone who is so willing to take their time to help! I'd like to answer all the questions starting with Was the Lexus dealer a registered one? or something to that effect. Yes, I believe they were, but this is Cambodia, and you can never be sure. We took it to another place who said GEARS, but I think they were basically saying the same thing as the Lexus place.

Driving conditions are HOT. Very hot! It's 42 degrees Celsius for half the day (I don't know the Fahrenheit conversion). It IS stop and go, stop and go, and rarely I am reaching more than 30kph / I guess that is about 20mph. Air con is on COLD (lowest temp setting) the whole time. I don't know what octane level is or how to check it...? I don't take anything with me other than my girlfriend and a few empty water bottles we've been procrastinating to clean out Sparks not serviced that I know of. I will look into the other things you have mentioned.

Since buying the car for $13.2k, it really has been nothing but problems and expenses, so I think we are probably going to sell it to a dealership soon and let them fix it. There are also more problems like the radio antenna isn't going back in, like it should and a high pitched squeeling when the car is stationary but in the reverse gear.

Thanks to everyone for your helps! This is a fantastic forum and group of people.

Also, I reset the MPG today, as I often do every week or 2. It was at 11.1mpg before I reset. After, I drove around town for 20 minutes, and checked. It was 9.5mpg. Great huh?
If you are indeed in bumper to bumper traffic and only going max about 18 mph (30kph) with full A/C (in 110F weather), then around 10 mpg is believable. I'd almost say it's to be expected.

Have you tried calculating mpg by hand? (i.e mile driven on tank/gallons to fill tank) The computer is not always accurate.
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Old 05-12-14, 02:54 AM   #14
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Quote:
Originally Posted by hypervish View Post
If you are indeed in bumper to bumper traffic and only going max about 18 mph (30kph) with full A/C (in 110F weather), then around 10 mpg is believable. I'd almost say it's to be expected.

Have you tried calculating mpg by hand? (i.e mile driven on tank/gallons to fill tank) The computer is not always accurate.
Not as such no. I rely on the computer. The check light has just come back on and I've noticed that when I push the O/D button, it does not come up on the display. I guess this is what the mechanic saying the gears are not correctly working is about. A little concerning. Things just go from bad to worse with this vehicle.
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Old 05-12-14, 03:38 AM   #15
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See what that code is as soon as you can before others pop up.
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Old 05-12-14, 03:38 AM
 
 
 
 
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