hello everyone let me start by saying i am new to this forum and have been extremely pleased with all the great threads on here, especially the technical ones.

That being said i have a question regarding the mpg on the 2004 5.4 trucks.

I currently have the cam phaser tick and had the rough idle until i changed my oil to a 10w40.

I know that you are supposed to run the 5w20 but i am running the 10w40 for a lil while til i get my parts in for the timing overhaul that i know i need because it helps the oil get past the leaking tensioner seals.

So know that you know the history my question is what mpg are you supposed to get with this model truck because when i first got it i was getting 11city and 15 highway...now that i changed oil to 10w40 i get 13 city and 20 highway.

My reason for the question is because after i do the timing and cam phaser job i want to run the proper oil but if im gonna go back to the lesser mpg doing so id rather stick with the 10w40.

Also ive been running it this way for a month now with no complications or check engine lights.
The cam phaser tick is still there but the rough idle has completely vanished which let me know i was on the right page with the leaking tensioner.

Thanks in advance, any and all responses are appreciated!

 

I see that ive got many views on my thread but no response... so to make it short can no one tell me what mpg im supposed to get with this truck?

 

As for MPG, it varies so wildly due to location, climate, terrain, and driving style that it's hard to say that one truck should get the same as another truck. I keep a very detailed track of my mileage ('06 SCrew FX4). You can see it by clicking on the banner image in my signature.

 

Thank you for your response that's all I was looking for...i wonder has anyone else experienced such a significant increase in gas mileage as I have by switching oil?

 

Now this is interesting. I have not heard of this before.

 

I know its extremely strange to me as well...that's y I had to ask u guys about the factory mpg y'all are getting....when I complete timing over haul on my truck I will switch back to factory recommended oil and see what the mpg are then and update u guys

 

I would have thought thicker oil would rob power netting less mpg not more?

 

I would generally say that the thicker oil would lower you MPGs, but if you had low oil pressure before you were probably not getting enough oil to the whole engine. Now that your engine is getting enough oil were it should, it is running properly.

I would caution you that running the thicker oil is probably just masking the bigger issue, and sooner or later you will need some major work.

 

I 100% agree its masking a bigger issue as I noted what the problem is and have already ordered the parts...the purpose of this discussion was simply to find out what fuel economy every one else was getting running the proper oil and having a stock setup

 

Basically, your MPG gain is a fluke, due to something else or there were errors in the MPG calculation process at one end or the other. A heavier oil would trend the mpg down but probably not enough to notice. It's certainly not directly responsible for any gains. If it induced any changes due to effects on the VVT, it would probably be to make the VVT work as it should. I've never heard of heavier oil fixing anything but noise but I suppose that doesn't mean it hasn't happened.

I run 10W30 in my '05... not because I think it's betterfor the engine, but because it's my "fleet" oil used on my farm (it goes in everything, from tractors to tillers and even a Honda Accord). I was worried what effect it would have on VVT, so I datalogged VVT operation for a period of time and discovered it made no difference at all. Hot oil pressure (I have a "real" gauge) is higher. Cold oil pressure is substantially higher due to the decreased cold viscometrics of 10W30 vs 5W20

Your current MPG numbers seem about right, depending on your driving situation, but I would ask how you came by them? MPG readout or calculated the old fashioned way (gal/miles=mpg)?. The electronic mpg readouts are notoriously optimistic because they are "should be" values calculated inside the PCM based on a couple of engine readouts. 13 MPG around town is really about right. The 20 highway is a little high but possible and, as was said before, there are too many variables to nail it down for everyone.

 

Thank you for the feed back on that...also I always do my own calculations on mpg but my calculations are precisely 5% lower than that of the hud in my truck and these are the numbers I shared with u guys...i fully agree that I've never heard of thicker oil increasing mpg that's y I wanted to know what I should be getting because I knew the 10w40 was helping with the leaking seals in the tensioners.

I'm no newb when it comes to engines and this was one of the strangest things I had come across but I've only owned this truck a couple of months and didn't know what mpg I was supposed to get... So again thank you ,I believe u answered by query completely.