Pennzoil 5w-40 kills my MPG!

[santov]

When I bought my Jeep SRT8 the dealer threw in a book of oil changes. I have 5 more coupons left. Last time I went in I got Pennzoil 5w-40.

I track my fillups with GasCubby and commute the same route often. I though maybe the first tank was just me driving faster then usual, but the average of the last 3 tanks has dropped from 15.6 to 13.9. That's more then 10%! I'm going to allow a couple more tanks and if it doesn't improve I'm draining the Pennzoil out and going back to M1.

Anybody else experience something like this? What would cause the MPG to drop? I hope not a different visc, or perhaps more drag.

 

[asiancivicmaniac]

What was in there before?

 

[StevieC]

Do your cheeks hurt when you try to suck a thick milkshake through a straw?

Similar to an engine designed for a thinner oil trying to get a thicker oil through the pickup tube and then push it up narrow oil passage ways.

Of course you are going to loose some MPG.

 

[garlicbreadman]

your dealer stocks 5w-40?

 

[Spyder7]

You average 15.6 mpg and your worried about mileage? Seriously?

 

[crazyoildude]

agree with Stevie

 

[Quattro Pete]

I find it hard to believe that oil viscosity alone could drop your MPG by 10%.

 

[Hemi426]

I would drop back to Pennzoil 5w-30 and monitor how much you use your air conditioning. That can be a mileage killer also.

 

[FZ1]

Sure. The synthetics have less friction so you may get better mpg. Synthetic oil pays for itself.

 

[MNgopher]

Not surprising. I lost over 7% using 5w40 Rotella T Synthetic in my '99 F150 versus the 5w20 and 30 I ran before and since. I tried it in a 1 year trial, and the UOA's showed virtually no difference.

 

[DC84]

Pretty sure the SRT models call for 0w-40 so 5w-40 shouldn't be a big deal. The Dodge dealer I worked for stocked 0w-40 Mobil 1 which is what Dodge said should be used. Check your oil cap/owners guide and see what it says. With more than 400hp in an SUV 14mpg isn't that bad.

 

[santov]

I guess I should have provided more background- Factory recommends Mobil1 0w-40. I had great life and results with that oil. After Dodge went bankrupt the dealer network switched to Pennzoil Ultra 5w-40. I know that the 5w being slightly thicker might be a little more drag, but 10% hit to fuel economy? How much more wear does that translate to? The drop in fuel economy is symptom to what cause?

Spyder7- I'm not worried about my MPG, I'm worried about the impact of switching to a untested (to me) brand is doing. If I said I was worried about MPG I'd be asking about a Prius.

 

[Johnny]

Half of BITOG is looking for Ultra 5W-40 and you have a dealer that stocks it. How long have they been doing that? Something else is causing the mileage hit, not the oil.

 

[santov]

Originally Posted By: Johnny
Half of BITOG is looking for Ultra 5W-40 and you have a dealer that stocks it. How long have they been doing that? Something else is causing the mileage hit, not the oil.


Dealer used Pennzoil Ultra 5w-40 Euro spec. The only thing that changed is the oil.

 

[asiancivicmaniac]

AC use before and after your oil change?

 

[santov]

Same (Auto usually has AC comp running).

 

[sprintman]

There are no engines 'designed for thinner oils'. Clearances are still basically the same as they always were, but tolerances have tightened up.

 

[Oldwolf]

Did your fuel source switch to Ethanol blends?

 

[Spyder7]

Originally Posted By: santov

Spyder7- I'm not worried about my MPG, I'm worried about the impact of switching to a untested (to me) brand is doing. If I said I was worried about MPG I'd be asking about a Prius.


Good point. FWIW my remark was a bad attempt at wit

More on topic, I think there are too many possible variables to attribute it to your oil switch though (and its impossible to control all of them in real world use.

I get 30 mpg on average, but its been as high as 35 and as low as 25. Some things I could easily account for on a given tank (more highway, less city). Other times I was at a total loss as to the fluctuation. And I not only stick to the same brand of gas, I also only use 2 different gas stations.

I no longer even bother to track it. I know 30 mpg is my average, and I know enough about techniques to extend it and habits that lower it. Tracking it for me just takes away from the enjoyment factor (too much hassle).

-Spyder

 

[HangerHarley]

Originally Posted By: Quattro Pete
I find it hard to believe that oil viscosity alone could drop your MPG by 10%.


Oh, but people think that, Pete. Some even use it as an argument AGAINST Thick Oil!

God forbid someone should put 20W-50 in a car. Maybe even one that runs smooth on it!

Ive found that Fuel Economy is the result of Tire inflation, and how good you are at being light on the gas - you can go light on the gas and fly. Trust me. Its all in the transmission and application of the gas, no brakes - and smooth. Also how much "Stuff" you have in yor car.

Engine oil protects your engine, so use what the manual says, or one grade thicker (10W-30 on 5W-30, 10W-40 on 10W-30 etc) if you have a higher-miles car.