I have a 5.0 in my truck. It ussaully gets 14.5 - 15 around town and 17 highway. But now it seems to 12 - 13 mpg no matter what.

It has 101,890 on the clock and changed the oil to Castrol "high mileage" at 100,300.

The oil I used before was just regular oil... I also use a fram filter too. But even with that I still got 17 mpg highway.

Also I have not changed the spark plugs or wires or distribor. Should I replace them to help?

Or could this be a timing problem and take it to mechanic?

Any help would be very much appreciated,
Thank you,
Rob

 

How long since the last tune-up? You dont have to take it to a mechanic to set the timing either, you can do just by ear, not as precise but it will do the trick. Does the truck run rough? mine was runing rough and i changed the plugs,wires cap and rotor with no luck, so i set the timing and still no luck. did a compression test and saw the problem, low compression on #8. pulled the heads off and seen a chip out of a valve. just waiting to get the heads back from the machine shop and it will be a new truck running on all 8 cylenders, yahooo. Oh and i run castrol oil in all my vehichles with the lucas oil stabilizer. works great. good luck with your truck.

 

Thanks cchimuk.

My truck does not run rough or anything abnormal, its just getting lower fuel mileage.

I have not done a tune up with the truck. I plan to replace the plugs, wires and distributor this weekend though.

Since I live in Cali, I am wondering if it could be the new oxygenated gas hurting my mileage?

 

- Thicker oil will cause a drop in gas mileage, but not that much. What weight are you running?

- Get rid of that POS fram filter right now and switch to a motorcraft. I wouldn't run a fram on a lawnmower.

- Do not set the timing by ear unless you KNOW what you are doing, and even then, use a timing light. There is a big difference between 8 and 12 BTDC and your ear probably can't pick that up.

Give it a tuneup (cap, rotor, plugs, wires, air filter, breather filter, fuel filter, PCV valve) and also change the O2 sensor if it hasn't been done in a while. Then report back with your mileage.

 

Hopefully you're not estimating milage with the fuel gauge.. it's nowhere near accurate and they tend to go wacky over time. Use the odomoter and fuel volume pumped on refills to calculate a real number.

 

I use a combo of fuel gauge, odometer and gas pump read out to estimate the miliage im getting its fairly accurate.

But to answer the question yes thicker oil will cause a drop in miliage. I am running 10w30 valvoline in my daily factory rated on the 78 2V 351 is 10 city and 17 highway. Currently I am getting 14 - 16 city with 15.8 city being the avg. Havent really drove her on the highway enough to get a highway figure but I figure round 20. These figures are with the tires aired up to the door tag recomended 28PSI but if I inflate them like I usually do to 32 PSI the max tire rating I can actually gain another 1/2 to 1 1/1 mpg. Reasion for that is the tires are not rated for a car as heavy as mine but they said they didnt have any stronger tires in the size.

On the timing I had the car set with timing light but I set her with a vacuum gauge to get the most vacuum since it was still saying late ignition timing when set to specs. I now got 24in hg vacuum and the engine runs smooth.

So you might want to check your vacuum with a vacuum gauge on manifold vacuum. Should be over 15in I belive if its less than that then you got late ignition timing you should really shoot for as much vacuum as possible. more vacuum generally way I see it means better economy.

 

In a 1995 5.0, the timing should be set at 10 BTDC.

 

Thanks everyone.

Conanski - I use the odometer/volume to calculate mileage and not estimating through the gauge.

I cannot time an engine by myself, so that will have to be done by a mechanic.

I use a Fram filter because it is always at Wal Mart, but next oil change I will go to Motorcraft. I will also tune up the engine, it needs it anyways.

Thanks again guys

 

Thing is though in a 95 truck with OBD I you cant time it the computer sets the timing though. you have to disconnect the computer from the dist and time it to TDC but the computer will set the timing to 10* BTDC or what ever it will be. I replaced dist in 89 E150 van 302 V8 and i just dropped it in in the same position the old came out never timed it the computer did it on its own.

If you leave the computer hooked up you move the dist the timing will change but then go back where the computer wants it at. Best bet is to hook a vacuum gauge to manifold vacuum make sure you have atlest 15 - 18 in hg vacuum if you do your timing is good. Only things I would check is the cap and rotor, spark plug wires, spark plugs, air filter.

 

I suggest you follow absolutely none of the advice in this post. Except for the last sentence, everything in it is wrong.

 

I wouldn't even run the Fram to the next oil change. Get a MC filter and change the filter. Not using a timing light to set timing is like shooting in the dark.