The Frequently Quoted “Taxi Study” SAE 2005-01-3818

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I know of only this study using taxis as the main experiment. I am going to review it here. Las Vegas taxi service was considered one of the most demanding environments for an engine lubricant in North America by OEM’s.
Evaluation of SAE 0W20 GF-4 Prototype Formulation in Severe Taxi Fleet Service, Damen, Broom, Hartley and Riley.

My preface: Over the years many have referred to “The Taxi Study” as a reference that HTHS levels less than say 3.5 will result in accelerated wear. No oil should be used if the HTHS is less than 3.5... Engines will not last 100,000 miles as CAFE is mandating the use of thin oils with HTHS of less than 2.7... The study is proof that they only care about CAFE and no longer about engine longevity... Forget about the probability that replacing a car every 100,000 miles will have a greater impact on the environment than 0.5 better MPG in your car or truck. And the list goes on.

The study used 4 vehicles running 0W20 and 4 using 5W20 experimental oils from Infineum USA. The oils were group II/II+ mineral based formulations. Each car was driven for 100,000 miles. They each had 10,000 mile oil change intervals in what was considered the most severe service, taxis with extended idle times, mostly start/stop service, hot 108F heat, and 3 times the recommended oil change times. Yellow Checker Star Cab service ran the 8 Ford Windstar 3.8L vehicles. The time was 12-18 months of severe service - a lot of stressful miles in such a short time if you ask me.

The oils: 100C viscosity 8.7-8.9, HTHS 2.6, Noack 13.3-14.9, ZDDP 0.05. Tests were engine tear downs, oil analysis and bench tests.

Results:
Iron levels were thought to be acceptable if below 100ppm and actually averaged 70 during the 10k intervals. Lead was 7, aluminum was 6, and copper was 22. The acceptable limits were 40 for lead, 50 for aluminum and 50 for copper. Remember that the oil change interval was 3 times longer than recommended!

Viscosities despite having early thinning actually exhibited oxidative thickening up to a viscosity of 10 at 100C (a 30 grade oil) at 10,000 miles. The HTHS also thickened to as high as 3.5. Certainly engines experienced both ends of the scale.

The fuel economy was statistically significant comparing the 0W to 5W oils with a 0.2 MPG difference. (Some say you should use a 5W over a 0W oil and better yet a 10W for wear reduction but that was not evident here).

Overall engine tear down results: Testing bearings, sludge, varnish, valve trains revealed “excellent” results. Lab and bench tests suggested “excellent” wear performance.

My conclusions.
I see no evidence “proving” that wear would be “excessive” if the HTHS was below 3.5.
Wear with the 20 grade oils, in the most severe conditions, was certainly not excessive. At 100,000 miles engines were nowhere near end of life.
If we were to use current 20 grade oils made from better base stocks and better additive packages one might expect even less wear.

ali
 
Well that’s good to know! When I bought my 07 Jeep 5.7 seeing as how 5/20 was required for the MDS system I started off with Mobil 1 & have had good results with it. Excellent UOA results. No cam/lifter issues.
 
The problem with so called Tests is that it means very little in real world driving. How many members here live in Las Vegas and drive a Taxi?
 
The problem with so called Tests is that it means very little in real world driving. How many members here live in Las Vegas and drive a Taxi?
It is well known that taxi service leads to longer engine life. As the engine remains at operating temperatures all day long. It is not unusual to see delivery vehicles, limo's and Taxi's with north of 400K miles, even with engines that don't last in other applications.

Consider that few taxi's spend any time at redline, or under any significant load at all. That's quite different from vehicles I own, that's for sure. On today's drive, I had the F150 at it's higher (tuned) redline a good number of times.
 
I know of only this study using taxis as the main experiment.
There is a similar study done just two years later by Ford and Connoco; SAE 2007-01-4133. It used taxis in Las Vegas; Ford 4.6L Crown Vics as I recall. The goal was to see how longer OCIs affected wear. It showed that longer OCIs (out to 15k miles) actually have an effect of lowering wear rates; they longer the oil was in service, the lower the wear rate went.


Las Vegas taxi service was considered one of the most demanding environments for an engine lubricant in North America by OEM’s.
I think that assumption has faded over time; the OEMs don't see taxis as the end-all-be-all worst case in today's world. And probably because these "taxi" studies have shown results proving that type service is not as destructive as the theory lead one to believe.


My conclusions.
I see no evidence “proving” that wear would be “excessive” if the HTHS was below 3.5.
Wear with the 20 grade oils, in the most severe conditions, was certainly not excessive. At 100,000 miles engines were nowhere near end of life.
If we were to use current 20 grade oils made from better base stocks and better additive packages one might expect even less wear.

ali
I would concur generally. Thinner oils don't make for high wear, despite the implied hysteria. In most cases, a lube with HTHS below 3.5 is not a kiss of death by any stretch.


I must confess, I don't really understand why you posted this thread, and the one below
You're discussing thinner lubes and SAE studies which, perhaps 15-18 years ago, people were concerned about.

There's nothing new here at all; this is really old news, is it not?
 
The study used 4 vehicles running 0W20 and 4 using 5W20 experimental oils from Infineum USA.
What kind of test compares two xW-20 oils if they are looking for wear differences based on KV100 viscosity? What was the HTHS of those oils when new? Not anything close to 3.5 cP I'd bet.

Viscosities despite having early thinning actually exhibited oxidative thickening up to a viscosity of 10 at 100C (a 30 grade oil) at 10,000 miles. The HTHS also thickened to as high as 3.5.
If the KV100 and HTHS thickened over the OCI, then that was helping keep the wear down.
 
My conclusions.
I see no evidence “proving” that wear would be “excessive” if the HTHS was below 3.5. Wear with the 20 grade oils, in the most severe conditions, was certainly not excessive. At 100,000 miles engines were nowhere near end of life.
Nobody can conclude that because the oils KV100 and HTHS increased over the OCI as you mentioned earlier. What if the HTHS was 2.6 cP to start with and thinned down to below 2.0 cP at the end of the OCI due to fuel dilution and shearing? What would the test results show in that case?
 
I’m not a fan of the taxi studies, only because normal driving is not consistent like Taxis are. They are used the same way everyday.

Most cars might be driving 1000 miles one day, and 1.5 the next…….
 
It is well known that taxi service leads to longer engine life. As the engine remains at operating temperatures all day long. It is not unusual to see delivery vehicles, limo's and Taxi's with north of 400K miles, even with engines that don't last in other applications.

Consider that few taxi's spend any time at redline, or under any significant load at all. That's quite different from vehicles I own, that's for sure. On today's drive, I had the F150 at it's higher (tuned) redline a good number of times.

I agree that most cabs are at or near op temp most hours of the day, but that shows that the old adage of wear at startup is the truth and that oil weight is irrelevant in the vast majority of newer real world applications.

So why wouldn't we strive for better fuel economy? Even construction vehicles are trending this way with increased use of 10W-30 HDEO over 15W-40, and even thinner sins being used at least in cold climates....

P.S.: I would add that construction equipment also undergo regular UOA's in a consistency that actually makes them useful at trending...
 
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If the KV100 and HTHS thickened over the OCI, then that was helping keep the wear down.

Perhaps, but there is no displacement of existing wear additives and it is possible that older zinc that has weather somewhat may protect better if drains are extended in warmer climates with few cold starts. But overall, I wouldn't say one study is the be-all and end-all of anything...
 
Chevron Havoline either participated in or did their own study with Las Vegas taxis.

I would tend to believe the conditions are severe. It’s not just the temperatures but the long idling times to run the A/C. Lots of short trips too.


 
I've been in taxi's in other parts of the world, but never here in the US. We always use uber or lyft here in the US. I can definitely tell you they all drive like bats out of hell and are very abusive to their cars!
 
I've been in taxi's in other parts of the world, but never here in the US. We always use uber or lyft here in the US. I can definitely tell you they all drive like bats out of hell and are very abusive to their cars!
In the SF Bay Area, cabs were decrepit, usually a Crown Vic from the police auctions but later the Prius/Camry Hybrid/Altima Hybrid or Escape/Fusion hybrid, whatever the cab operator gets from the auctions cheap. They would lease those cabs out to their drivers and do the absolute minimum of maintenance.

Uber and Lyft drivers have more of an incentive to maintain their cars - I’ve seen a Jiffy Lube/Oil Changers or dealership service department sticker on many, Lyft does oil changes(and gives their drivers a small break if they have status with Lyft Rewards). It would be interesting to see an oil study on cars used for Lyft or Uber, IMO.

The cab tests are at least repeatable and “constant” since the car fleet doesn’t change and the use cycle also doesn’t change. Chevron often quotes taxi fleets for Havoline motor oils and ATFs.
 
In the SF Bay Area, cabs were decrepit, usually a Crown Vic from the police auctions but later the Prius/Camry Hybrid/Altima Hybrid or Escape/Fusion hybrid, whatever the cab operator gets from the auctions cheap. They would lease those cabs out to their drivers and do the absolute minimum of maintenance.

Uber and Lyft drivers have more of an incentive to maintain their cars - I’ve seen a Jiffy Lube/Oil Changers or dealership service department sticker on many, Lyft does oil changes(and gives their drivers a small break if they have status with Lyft Rewards). It would be interesting to see an oil study on cars used for Lyft or Uber, IMO.

The cab tests are at least repeatable and “constant” since the car fleet doesn’t change and the use cycle also doesn’t change. Chevron often quotes taxi fleets for Havoline motor oils and ATFs.
These drivers we've been with act like they're driving to a three alarm fire! Flooring it, stabbing the brakes, flying over potholes and speed bumps, ouch!
 
I've been in taxi's in other parts of the world, but never here in the US. We always use uber or lyft here in the US. I can definitely tell you they all drive like bats out of hell and are very abusive to their cars!


The Uber and Lyft type operations are prevalent in many cities around the world. Some countries have their own business
 
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