Fuel economy and RPM of 99 Solary SE

[smatoska]

I've noticed a dramatic drop in fuel economy in my 99 Solara. It's just your basic V-6, 3.0 ltr. but I also noticed I am running about 2900 RPM at 75 MPH. I was driving a buick the other day and noticed that at 75MPH the RPM was only 1900. Do I have a problem with my transmission, that it is running so high an rpm or is this normal for the toyota's. I don't want to take it to the shop as the shifting is still smooth and I have no problems, but I went from 30 mpg to 23. Everything is stock, although I put bosch platinum plugs in and replaced the spark plug wires, but fuel economy dropped, and I thought it would get better. I have great performance with car, just would like to get my fuel economy back. Any suggestions?

[Turbosolara]

when i am driving 75 mpg, my rpm is at 3500. i have a 02 lexus IS300 5 speed manual. but i can assure it it is like this since day one although i brought used.

my point is every car has different rpm at different speed. the different is caused by different gearing.

how many mileage is it on your car?

[unbalancedwood]

probably those Bosch spark plugs...ngk or denso all the way...

did this happen immediately after the change in plugs/sparks?

The rpm thing is really weird though, at 80mph i know im at 2900/3000rpms

[Turbosolara]

my guess is that you have improper gap on your spark plugs and you are running rich.

[DatSRBoi]

1900rpm at 75mph? If thats true not many cars can do that.

[Jakecallun20]

Was that Buick a V8? They don't run as high as the V6's.

[Down2TheC]

RPM to Speed is a fixed relationship and has nothing to do with mileage beyond the intial design of the trans. Only time you need worry is if you find you can do the same speed with different RPMs.

i.e. My 4runner has a 3rd gear that never locks up. I can be cruising and ease off the gas a bit and the RPM drops 500-1000 rpm without a change in speed. That leads to terrible mpg. But no Solara has such issues. Only the old trucks had that crappy trans.

So if your mpg changed drastically, look at your air filter and check the ECU for failing sensors and plug misfires. They can cause waste. Probably not mechanical though.

Isn't 23 about right for the V6? Maybe you're just not on the highway as much?

[Jakecallun20]

^^ I agree, I think 23 is about right for the 1mz V6 motor. I average about 22-24