Excessive Fuel Dilution of Oil

[ekpolk]

Well, I just got back my second UOA for my Prius (owned since last summer). I've already entered the data over at BITOG, so rather than retype, here's a link: Click here.

To summarize, I logged 5800 miles on this fill of Pennzoil Platinum synthetic 5w-30, finishing the OCI with an 1800 mile vacation trip from Pensacola to Key West and back.

What's alarming to me is the fuel dilution. More so since I drew this sample about 20 min after completing the vacation trip, when the engine should have boiled off a maximum amount of fuel and other aromatic contaminants. Yet the fuel is still almost 2%. It could well be 2-3x that in normal usage. Hot viscosity is down into the 20 wt range as a result.

On the upside, while I've got dilution, clearly, I have no damage showing up yes, actually, quite the contrary.

Here's the scary part: my oil analysis guy says he has seen multiple examples of Prii with substantial fuel dilution of the oil. Now, I have no way of knowing for sure, but this certainly could be a good reason to explain why, while almost all other contemporary Toyotas are being spec for xw-20 oil, the Prius has remained a 5w-30 car. If I had run a fill of 20 wt oil in this instance, I'd probably be approaching a 10 wt and have a crankcase full of something close to kerosene.

I do realize that some here have run 20 wt oils without apparent damage. Has anyone else here seen excessive fuel in their oil on UOA?

[ScottY]

I've done two UOA's, once hot (engine on for more than 10 min), once... well... warm (engine was on maybe 5 min). The hot sample contained 1% fuel, while the warm sample contained 0.8%. What's the fuel amount in other normal gas engine UOA's? The vis @ 210F were 56.5 and 59.8, respectively. I use M1 5W-30 by the way.

On the topic of sodium, dealer oil is suspected to contain high amount of sodium. The first UOA after I switch from dealer oil had 50ppm of sodium. The UOA after that, sodium level dropped to 4ppm.

I don't use 20 weight oil, so I have no experience.

[Bill Merchant]

Here's a question for you oil afficionados: Could the Atkinson cycle put more fuel in the oil than the Otto cycle? Does the Prius ICE rebreathe the fuel vapors? Where did the fuel go in the warm sample?

[ScottY]

maineprius947 compiled a spread sheet with all the UOA's posted on PC, http://priuschat.com/index.php?showtopic=27461

From that, seems like couple of UOA's contain pretty high fuel amounts.

Bill, I have no idea how to answer your question. I think only the engine experts would know. I guess taken the sample at different condition will be enough to produce the 0.2% difference? Just to be clear, the two samples were taken 9 months apart.

[iaowings]

Ok wow. I have no idea of exactly what was just said. I sort of get the point. You guys sound like medical personnel running and discussing labs on people. I am not knocking you guys in anyway at all to tell the truth I am farley impressed and feel I learned something from this post. Thanx.

[ScottY]

IAO, no worries if you don't understand. I started fresh when I have my Prius. This is my first new car out of college, and the first car that I actually take care of. If you want to learn more about used oil analysis (UOA), visit Blackstone Lab's page, http://www.blackstone-labs.com/gasoline_di...eport_expl.html. You'll get some basic idea what all these numbers mean.

[dmckinstry]

<div class='quotetop'>QUOTE(ekpolk @ Apr 4 2007, 09:08 PM) [snapback]418002[/snapback]</div>

Well, I just got back my second UOA for my Prius (owned since last summer). I've already entered the data over at BITOG, so rather than retype, here's a link: Click here.

To summarize, I logged 5800 miles on this fill of Pennzoil Platinum synthetic 5w-30, finishing the OCI with an 1800 mile vacation trip from Pensacola to Key West and back.

What's alarming to me is the fuel dilution. More so since I drew this sample about 20 min after completing the vacation trip, when the engine should have boiled off a maximum amount of fuel and other aromatic contaminants. Yet the fuel is still almost 2%. It could well be 2-3x that in normal usage. Hot viscosity is down into the 20 wt range as a result.

On the upside, while I've got dilution, clearly, I have no damage showing up yes, actually, quite the contrary.

Here's the scary part: my oil analysis guy says he has seen multiple examples of Prii with substantial fuel dilution of the oil. Now, I have no way of knowing for sure, but this certainly could be a good reason to explain why, while almost all other contemporary Toyotas are being spec for xw-20 oil, the Prius has remained a 5w-30 car. If I had run a fill of 20 wt oil in this instance, I'd probably be approaching a 10 wt and have a crankcase full of something close to kerosene.

I do realize that some here have run 20 wt oils without apparent damage. Has anyone else here seen excessive fuel in their oil on UOA?
[/b]

My first sample test indicated fuel dilution. Someone suggested that it might not have been run hot enough to evaporate it away. This was after 1000 miles of use of Penzoil 5W-30. I just sent in a sample of the same oil at 5000 miles. I'll see what the report on that is.

Dave M.

[ekpolk]

<div class='quotetop'>QUOTE(dmckinstry @ Apr 5 2007, 12:40 AM) [snapback]418058[/snapback]</div>

My first sample test indicated fuel dilution. Someone suggested that it might not have been run hot enough to evaporate it away. This was after 1000 miles of use of Penzoil 5W-30. I just sent in a sample of the same oil at 5000 miles. I'll see what the report on that is.

Dave M.
[/b]

Dave:

Two thoughts on this. First, I pulled this sample at the exact moment when fuel dilution should have been at its absolute lowest -- literally 20 minutes after my wife and I had finished driving from Key West to Pensacola (over 700 miles). Hours of doing ~80 on I-10 should have burned off all the fuel and any other volatile contaminants. This leads me to believe that my dilution is probably substantially higher in normal day-to-day driving. Second, my oil analysis guy (Terry Dyson, great guy, knows his stuff, highly recommended) says he's seen a pattern of this in other Prii. On the other hand, the wear metals pretty clearly indicate that I had not reached the point at which dilution compromised the oil sufficiently that it caused damage. My car is cert used, so I'm staying with 5k OCIs for now, but I think this result is a "wake up call" that those who are running longer should watch things carefully and be perhaps cautious about experimenting with xw-20 oils.

Scott:

My other cars, and many others I've seen reports from in the BITOG UOA forum, usually show zero or mere trace indications of fuel. It's usually considered an indicator of a problem of some sort (PCV problem, failed thermostat not allowing engine to reach op temp, etc).

Bill:

That's a tantalizing question. I've just installed CAN view v3 (couple nights ago). It has readouts for fuel flow and injector performance. I'll be watching those parameters to see if they lend any clues. Atkinson cycle operation might have something to do with it, but that will be hard to determine for sure.

IAO:

I invite you to join us at Bobistheoilguy.com. See the link I posted above. We are a somewhat obsessed bunch... Anyway, we have a used oil analysis subforum in which hundreds of results are posted (maybe thousands by now). You can casually peruse them and get an idea of what is good, bad, ugly, normal or abnormal, etc for given engine types. It's fun, and it's nice to KNOW how your engine is doing vs just changing oil and hoping you don't have any lingering problems you can see until it's too late.

[dmckinstry]

<div class='quotetop'>QUOTE(ekpolk @ Apr 5 2007, 03:32 AM) [snapback]418116[/snapback]</div>

Dave:

Two thoughts on this. First, I pulled this sample at the exact moment when fuel dilution should have been at its absolute lowest -- literally 20 minutes after my wife and I had finished driving from Key West to Pensacola (over 700 miles). Hours of doing ~80 on I-10 should have burned off all the fuel and any other volatile contaminants. This leads me to believe that my dilution is probably substantially higher in normal day-to-day driving. Second, my oil analysis guy (Terry Dyson, great guy, knows his stuff, highly recommended) says he's seen a pattern of this in other Prii. On the other hand, the wear metals pretty clearly indicate that I had not reached the point at which dilution compromised the oil sufficiently that it caused damage. My car is cert used, so I'm staying with 5k OCIs for now, but I think this result is a "wake up call" that those who are running longer should watch things carefully and be perhaps cautious about experimenting with xw-20 oils.

Scott:

My other cars, and many others I've seen reports from in the BITOG UOA forum, usually show zero or mere trace indications of fuel. It's usually considered an indicator of a problem of some sort (PCV problem, failed thermostat not allowing engine to reach op temp, etc).

Bill:

That's a tantalizing question. I've just installed CAN view v3 (couple nights ago). It has readouts for fuel flow and injector performance. I'll be watching those parameters to see if they lend any clues. Atkinson cycle operation might have something to do with it, but that will be hard to determine for sure.

IAO:

I invite you to join us at Bobistheoilguy.com. See the link I posted above. We are a somewhat obsessed bunch... Anyway, we have a used oil analysis subforum in which hundreds of results are posted (maybe thousands by now). You can casually peruse them and get an idea of what is good, bad, ugly, normal or abnormal, etc for given engine types. It's fun, and it's nice to KNOW how your engine is doing vs just changing oil and hoping you don't have any lingering problems you can see until it's too late.
[/b]

Thanks for that additional information.

Dave M.

[dcoyne78]

Hi,

I also visit bitog from time to time (dcoyne78), what is the mileage on your Prius, would a stuck PCV cause fuel dilution? So far I haven't had a problem, but I am not paying for Terry Dyson's Analysis, maybe the Blackstone numbers that I have been getting are not correct. I don't add anything to my oil, I'll be posting a 10K result in about a week, so we'll see if I am still ok. I also plan to replace the PCV valve soon, though this may have nothing to do with fuel dilution. Terry has also recommended a Fram air filter for Honda's with fuel dilution problems, so if a Fram air filter is available for the Prius, it may be worth a try. I know Terry's advice is proprietary so you can't share Terry's tips for solving this problem with us without his permission. One indicator of fuel dilution is low flash point, so I will test this theory on my next oil change by using a Fram air filter, if available.

Dennis