1983 Riviera mileage

[Guest mstanleyfl]

I have a '83 convertible. Don't really drive it hard but I only get about 10 - 11 MPG. Is this normal? Any suggestions..

[RivNut]

Not at all.

I've had 5 different 6th generation Rivieras, all with the 5 liter Oldsmobile engine and the worst I ever got was 15 and that was in the mountains of WV on the way home from the ROA event in PA. On the road, I could usually get close to 20 mpg out of any of them on the highway driving the speed limits. I did NOT drive them like a muscle car or even think they were any kind of performance vehicle.

Ed

[Guest merrillcrosbie]

I also have an 83 convertible, but mine is the 4.1 V6. When new with the 205/75-15 tires I was getting an average of 20 mpg. When I replaced the tires I upgraded to 225/70-15 and my mileage dropped to about 17. Seems like a 15% drop in mileage for a slightly wider tire is a bit extreme, but that is what I am getting now. On road trips that are primarily freeway speeds I can get 21 mpg as long as it is under 75 mph. Over 75 and my mileage drops significantly. (Probably because the tranny keeps it in 3rd gear rather than OD to maintain the higher speeds...these things are not at all aerodynamic.)

[sosuzguy]

Do you ever have black smoke come out or does the tail pipe throw soot out after a cold start? Exhaust smell rich? I guess your "Check Engine" light isn't on indicating a Rich exhaust condition?

You can still pull the codes to see if any have been stored in the past.

[63 Rivi]

I was getting about the same mileage when I bought my used 85 last year. When I tore into it, I found the following:

-vacuum leak at the back of the carb

-vacuum hoses that were dried out, cracked and leaking vacuum

-carburetor in a bad need of a rebuild (m/c solenoid was not working)

Assuming that the engine is sound with good compression and it has had a tune up, I would do as Jayson said and check the computer for codes first. Make sure you are getting "12" to ensure the computer is working properly. Any other codes, write them down and check the FSM. If ok, then check the vacuum lines next. Pull them off one at a time and look at each one of them, since many times they are cracked underneath. Next, I would check the carb. Start the car and take the air cleaner lid off. Make sure you hear the tick-tick-tick sound while it is running. If not, the mixture control solenoid is bad. Also, check the sensors and the connections for corrosion, replace the oxygen sensor if it is original. You want to make sure the computer is getting the proper information. Another issue is the catalytic converter. They get plugged over time and can cause a restriction. Do a back pressure test to confirm operation.

I fixed my 85 and drove it to Lexington (round trip about 1700 miles), and averaged 21-23 mpg. Not bad for a motor with 160k on it. Any other questions, just let me know. Good luck.

Edited July 22, 2013 by 63 Rivi (see edit history)