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Lost 8 Mpg After 90k Service


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After having the timing belt, water pump, cam seals, distributor cap & rotor, drive belt and air filter replaced, I am only getting 20 MPG (HWY) whereas before I was getting 28 MPG (HWY). The 28 MPG was with a real dirty air filter too! I replaced the air filter with a K&N.

The car idles between 600 to 800 rpm in park once the engine has ran for a minute or two . However; I do feel the car is idleing to high when driving.

I am taking the car back to the mechanic because the A/C fans are on all the time and he used the green anti-freeze instead of the Toyota orange brand.

Any idea what could cause this problem?

Thanks In Advance !!!

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Just a couple of guesses........

I've heard the MAF needs to reset (disconnect battery) if you change filter type so it may take a tank or two...

Also, if the fans are trying to keep engine cooler, that will cost you MPG. Did the mechanic fill the antifreeze up through the thottle body first, then top off in reservoir? Also, the car needs to be brought up to normal temp with the heater on 85 and reservoir cap off to release trapped air....then top off. Maybe its got some air trapped in it?

Yes, use the pink toyota long life coolant!

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I do know the battery was disconnected because all of my radio and seat presets were wrong.

Not sure how the anti-freeze was added. What can I do to release trapped air? Start car with temp at 85 and remove reservoir cap?


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i agree, some says new filters give you better mileage, and i heard some say that a new filter lets more air in, so more fuel comes in to match the ratio of air to fuel. and K&N filters does give you a drop in MPG.

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Hmmmm, I wouldn't say the K&N filter drops your MPG. It actually increase it. I've used K&N filters in most of my cars. I put them in my past Nissan 300ZX's and they do make a marked improvement. More HP and better MPG. I haven't put one in my LS400 yet though. You must remember that the air to fuel mixture is controlled by the computer (ECU). If there is more air present then the ECU will actually lean out the fuel mixture, especially when not needed (i.e. freeway). I would say drive the car for another week or 2 then see if your MPG increases. The computer has to re-train itself. This is normal.

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.....I am taking the car back to the mechanic because the A/C fans are on all the time and he used the green anti-freeze instead of the Toyota orange brand.....

for AC fans 'constantly on' issue, have your mechnic check whether AC fan temperature sensor is actually connected to the socket at bottom of radiator or not. it could be accidentally left off when TB job was performed. that's was exactly the cause of my situation.

the location of the sensor socket:

as for green coolant, review this thread:

if you decided to go back to red coolant, make absolutely sure the green coolant is 100% flushed out (including the 50% trapped in engine block and heater core). if the red coolant is contaminated with green coolant, the coolant life is reduced to 2-year 30K miles instead of 5-year 150K miles the red one is rated for.

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quote from:

Straight ethylene glycol freezes at about 8° F, boils at 330° F, and carries heat about 15% less efficiently than water. But when mixed in equal parts with water, it creates a coolant well-suited to year-round driving for most applications.

The recommended 50/50 mixture of EG and water provides freezing protection down to -34° F and boilover protection to 265° F in a radiator with a 15 psi cap. If the proportion of antifreeze to water is increased to 70% EG and 30% water, the freezing point drops to -84° F and the boiling temperature goes up to 276° F. Mixtures greater than 70/30 are not recommended because the coolant's ability to carry heat declines as the proportion of antifreeze increases.

Straight EG antifreeze should never be used in an engine because it may allow the engine to overheat. Likewise, straight water should never be used because it provides no freezing, boiling or corrosion protection.

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