Mal58 replied:

Anthony,
I have a Prado GXL. I achieve typically around the 14-15 lt/100km. Fuel economy, however does occasionally take a dip for the worse (18-19 lt/100km). I believe that I can correlate it to a couple of things,
1) Disconnecting the battery for an extended period of time (ie. while working on electrical things eg dual battery system, driving lights etc),
2) Particular brands of petrol,
3) Using the Air conditioner in stop start city traffic.

Having taken the above into account, I would check your calculations for the change in speed. I did a quick check based on the RV trye size (215/80/16) cf your new tyres. I did this at,

http://www.fernblatt.com/longhurst/tyre_bible.html

This is an increase in 7.4%. You have to take this into account when working out how many kms you have actually covered compared to the speedo reading. (ie speedo = 100 km, actual distance = 107 km)
The other thing you should check to, is tyre pressure as I have found that this makes a big difference. I assume the Coopers are an A/T and should be run at a higher pressure than the ADR placard states for the original Grandtreks.

Hope some of the above helps,
Rgds,
Mal58

Rob P replied:

Anthony,

You probably have already checked this but make sure that your air filter is clean. Recently I was suffering very high fuel consumption (18 to 19L/100Km around town)in my Prado. After giving the air filter a thorough clean, my consumption dropped down to around 14 to 15 L/100km which is normal town driving. Hope that helps...

Cheers

greg replied:

Anthony a roof rack can make as much as 1-2 kpl difference depending on the wind direction. Driving technique can also make a big difference along with wide tyres.

Mal58 replied:

Anthony, I am a memeber of the toyota prado discussion group on yahoo. I new post came in the last few days about toyota deisel owners having poor fuel economy. Within the reply, was some information concerning Petrol as well. I have copied and pasted for your info. "....and the sensor reading inaccurately causes increased fuel consumption. Many petrol Toyotas also have had problems with oil hitting their MAP sensors (a pressure sensor on the intake side). How do you check for this? Unplug and Unscrew the air intake temp sensor carefully (Its the 24mm hex thing sitting above the throttle valve) and look at the bottom side of it for any black oil. I would be surprised if you didn't have oil smeared over the sensor....." The reply also mentions that the problem can get worse if doing four wheel driving where the vehicle is on acute angles. Possibly worth a check.
Rgds, Mal58

Mark replied:

Hi Anthony

I have a 97 RV6 as well. It has OME, no racks, and exactly the same tyres! I have only had the car for a few months, and when I first checked the economy it was about 22l/100km!! around town driving conservatively. The last check I did was 18l/100km around town after a highway trip. I have just put some injector cleaning stuff in the fuel and plan to get Toyota to do a gas test on it - apparently there is an adjustment that can be easily made to fix mixture problems. Also there is a hot-wire oxygen detector behind the air filter casing that can be checked for dust etc.(hope there is none there!).

It has done 112000km now and I am considering a comprehensive service to try to get much better fuel consumption.

On another matter, Toyota has agreed to install a boom vibration kit free of charge! I get the 2800rpm vibration in all gears. All I did was ask!!

All the best
Mark