Dear NL, kindly help with this:
It seem to me that the fuel usage of my Sienna is high. So, I met with a different mechanic who checked my exhaust pipe(for fumes deposits) and advised I change my Air Flow Meter. Well, I'm not convinced.

martinscheng:
Dear NL, kindly help with this:
It seem to me that the fuel usage of my Sienna is high. So, I met with a different mechanic who checked my exhaust pipe(for fumes deposits) and advised I change my Air Flow Meter. Well, I'm not convinced.

On what technical basis is that Kazeem asking for change of maf.If there is no technical test or troubleshooting dine then you are dealing with a typical part changer
I will advice you flee from any Kazeem that advise you to change parts and no technical basis for it ,unless you want to waste money buying parts u don't need .
Go and diagnose the issue first .
What usually causes extreme fuel mileage
1. Wrong air fuel mixture stoic - Lean or rich mixture
2. Running the car at low engine temperature- Fan run direct
3.Misfires -bad compression ,coils ,fuel pressure issue, injectors issues,vacuum leaks etc

thanks alot bro.
well, I have not done any diagnosis on the ride since it was purchased about a year ago. However, I will appreciate it if you could expansiate on the 3 points u mentioned that causes fuel mileage. Just so you know, my fan runs directly. I was advised to remove the Thermostat and run the fan directly when I had severeal issues with overheating shortly after I bought it.

martinscheng:
thanks alot bro.
well, I have not done any diagnosis on the ride since it was purchased about a year ago. However, I will appreciate it if you could expansiate on the 3 points u mentioned that causes fuel mileage. Just so you know, my fan runs directly. I was advised to remove the Thermostat and run the fan directly when I had severeal issues with overheating shortly after I bought it.

Tackle the fan run direct first but the way you go about is that u need to resolve the hidden overheating first before you can restore the fan to normal and install thermostat or else you will wake up the overheating that has been suppressed all this while .
Get a professional mechanic that can has a cooling system pressure tester to confirm the integrity of the cooling /radiator system before the restoration of the of the fan.
It will be difficult for me to expansiate on other points if you don't understand the fundamental but I have done some justice to some areas before ,u can go Tru this
https://www.nairaland.com/3729134/let-discuss-cooling-system-overheating
Below is the pic of cooling system tester .

Hello sir, I would advise you don't use the road sides mechanics anymore.. please and please go to the professionals ... They will diagnose ur vehicle for free and tell u what and what is needed to be done ... I promise u , u will never complain of this and certainly thank me later... Please visit GOF AUTOS... They are specialist and very very cheap.. office is at ikeja. Google their address.. when u get their , ask of Mr Richard.

Hello Sir. Good day to you. I use a 1999 toyota camry. After flushing my radiator some months back at a car wash, the water pressure from the nozzle destroyed the cells of the radiator (due to weakness i guess)

So I had to change the complete unit (inclusive of fan and thermoswitch ). But I later observed the fuel consumption began to increase and the temperature gauge was always extremely low even with AC switched on irrespective of distance I travel and intensity of heat from sun.

Met few kazeems who told me ''Bros, your engine go last well well becos him head go dey kool well well''. But as car user, and literate, I know this is purely abnormal and my online research, coupled with one of your responses states that if a car does not operate at the normal temperature, it would result in reduced fuel economy and the engine will wear out.

So, I embarked a DIY, surveyed the engine bay and realized the fan runs consistently making the engine over-cool due to disconnected thermoswitch. So what did was to plug the connector and Lo and behold, the temperature stays at normal level because the fans would only operate when the temperature reaches its apex.

But, the challenge here is this:Having connected the thermo-switch, I did a personal observation with the bonnet open while the car was idling. I noticed that when ever the temperature reaches it's limit, the fan operates at perfect and full speed. But once I switch on the AC, the speed reduces.

This has been a major challenge for me using the AC. The AC system is excellent. Thought it was the AC unit not until i took it for an inspection that I confirmed it is very perfect. The compressor was loosed...assessed by a highly reliable engineer and certified it is in perfect condition.

He however advised I consult a good engineer as regards the reduction in fan speed when ever the AC is working. According to him, the AC system requires good suction of Air through the condenser whenever its working.

Took it for scan, the following are the results

P0105
P0401 and
P0/1..... (not sure) but its meant bad downstream o2 sensor

But asides these results, I am still concerned about the reduction in speed of the cooling fan when the AC is operating

Sir, please advise. Is this normal?

Regards

I appreciate eagle eye car owners ,your observation is right for the fan speed for both condition of ac and maximum engine temperature threshold.
The fan speed is at low speed when the AC is on and fan speed is at highest speed when the engine temperature reaches the maximum temperature ,that is actually how the the car is designed to work nothing is wrong with the system ,however let me take your time to elaborate more on the working design of the fan according to the manufacturer specification.

Toyota Camry 2000 cooling system fan is such designed to be a 2 speed system :Low and high speed.
And there a certain conditions that must be fulfilled to achieve any of these speed .
1.Low speed : To achieve low speed ,what it takes is for the AC to be on and the AC refrigerant pressure below 188 psi .
2.High speed : Engine coolant temperature of above 95 centigrade and the fan speed will go to the maximum full speed and also the second condition to achieve maximum speed is for the AC pressure to go above 220 psi .
Therefore the fan will automatical achieve the highest fan speed @ ac on when the refrigerant pressure increase and the condition that increases pressure are : increase in ambient temperature , increase in engine temperature and there is already a sensor that tell the ECU when the pressure increases ,so I will advice you leave your fan alone at it's default condition,you don't need to tamper with anything ,
it is self regulating and self monitoring .

Thanks so much autologic. I am very grateful. Now, i rest my case