Got a 98 1500 with the 5.2 auto. gets about 10mpg. Im thinking it should atleast get 13 or 14 in town??Truckdoesnt use any oil. But when i did change it last i could smell a strong scent of gas in the oil. Plugs and wires were changed last sept. I have the 14" round air cleaner on it. What is the cause of the gas smell in the oil and why is the mpg so crappy. I thought maybe the plenum gasket but like i said doesnt use oil. I did check by looking down the tb and saw no pools. Thanks Eric

 

I have a 99 5.2 with no preformance mods, sept a chip. 5.5 fabtech lift with 35"s, i just did my calculations and got 7-almost 8Mpg town. Mabey could if you drive like a grandma?
Did i mention i try to race everytime i see another car? yeah its not for racing...

 

Thats funny cause i did try to drive like a grandma for a whole very long week and got almost 1 mpg better. Thats when i figured it wasnt worth it. lol. Not too concerned about mpg just thought it might help diagnose the issue with gas in the oil. I mean I did buy a truck and not a hybrid!!!

 

Just because it doesn't appear to be using any oil doesn't mean you don't have a blown plenum gasket.

Take off the air cleaner for a few minutes and look down past the butterflies. If you see oil pooled in there anywhere, the gasket is blown. (However, a thin sheen of oil is fine.)

I get 11-12 MPG in town, and I drive like a maniac and have the 5.9L. Granted, I only have 265s for tires and stock ride height, but still, that 318 should be getting much better mileage than it is. Have you done a tune-up recently? New distributor cap, rotor, and maybe spark plugs and spark plug wires? I improved my MPG by about 0.5-1 by doing a tune-up.

 

You mention that you don't see oil pooling in the plenum so I would say you don't have a blown plenum gasket. However, dirty sensors and corroded electrical connections could cause incorrect signals to be sent ot your ECM.

So in addition to a good tune-up (cap, rotors, plugs, air cleaner, & wires - if the wires are old) buy yourself a can of carb cleaner, a tube of di-electrical grease, and a new throttle body gasket. All 3 should total less than $15. . Pull your throttle body, remove the 3 sensors (IAC, MAP, and TPS) on it, and clean the throttle body and the sensors with the carb cleaner. Do a search here on the forum for additional comments about cleaning them.

Then inspect each electrical connsection you can find. If there is corrosion use a small pocket knife and scrape the corrosion out as you can and apply di-electric grease before re-attaching them. Don't forget the Crankshaft and Camshaft Position sensors.

I'm not sure how much this wil lhelp, but it will allow the sensors to provide information to the PCM as accurately as possible and hopefully improve your fuel mileage.

 

Thanks for the ideas. Hopefully next friday I can get the tuneup done.

 

seafoam.