Why gas mileage dropped almost in half?


After the water pump and timing belt was replace on my '94 gold edition V6 Camary, the gas mileage went from 27 to 30 miles to a gallon to 17 or less. None or the mechanics or dignostic machines can find a problem, it runs great and that there is nothing wrong with it. To me it is very wrong, especially in these days.


There is always the chance that it has to be taken apart and done right this time. The valve timing is probably retarded now or advanced. They missed by quite a bit if their work is the cause.


I fear pleasedodgevan is correct. You might get lucky and someone may find a loose vacuum hose or a disconnected sensor somewhere, but it does sound like a timing problem to me.


I agree that the likely cause is an improperly installed timing belt. If it is “off” by a few cogs, this can screw up your valve timing enough to make a difference like you have noticed. (And, in the long term, it is probably not very good for the valves themselves)

Take your CAMRY back to the mechanic who installed the belt and tell him that you believe that it was not installed properly.


I did take it back to the mechanic and the timing was set correct. And since then I replaced some oxygen sensors. Thanks for your replies. I have been thinking about attempting to trade it for something that can be converted to run on cooking oil if the solution stays completely evasive.


If the mileage has legitimately dropped that much (based on accurately measuring this of course) then the problem is likely that the timing belt is off a tooth or two OR the ignition timing as set by the distributor is not correct.
When setting the ignition timing the test plug must be used or the timing will be way off.

I would add that probably a fair number of mechanics will simply mark the distributor and reinstall it on the same mark without even checking the timing. This should never be done and is no guarantee at all the timing will be as it was originally.

Connecting a vacuum gauge to the intake could show both a problem with the timing belt installation or the ignition timing. Again, many mechanics do not use a vacuum gauge.
All of this is very easy to do and if your mechanics do not understand any of this process then you should find one who does and ignore the guys who did this.


I did take it back to the mechanic and the timing was set correct.

How do you know for sure it is correct. It certainly does not sound right to me. How does that mechanic explain the loss of mileage?