Fuel Dilution

[uraniumrich]

I'm wondering if anyone else has noticed a significant amount of fuel dilution in their oil analysis? This is my third oil change (with analysis with each change). While the change interval was a little longer than I'd like (5,543 miles), I was surprised to see what seems like a significant amount of fuel in the oil. As a result, the flashpoint of my oil was down significantly. Beyond stating the obvious - fuel is the enemy of our oil - can anyone shed some light on potential causes?

Just a little background on this oil change. The change was completed after a 6 hour road trip in very cold weather. We finished the road trip on a Monday night, the engine sat overnight, and then I changed the oil the next day (in other words, the engine was cold.) The temperature in my garage was kept in the 40-50 degree range. I had to choose between changing the oil a little early (about 4,500 miles) or a little late (5,500 miles). Given that I'm using high quality oil (Amsoil Signature Series), I wasn't overly concerned about the extended change interval.

Any thoughts on this?

 

[ultane]

I am NOT an expert on this subject matter.

Both oil analysis’ that I have done (SPEEDiagnostix) had small amounts of gasoline in it. The second oil change had slightly more.

This does concern me for potentially shortening the life of Miss Daisy.

 

[Doggman1525]

Is it possible that air was so cold that the engine oil never got hot enough for the fuel to fully evaporate and go out the crankcase? To my idiot level of understanding some amount of blow-by is pretty much inevitable which is why running a warm engine for a certain amount of time is needed for that sneaky fuel to vaporize and be removed through the crankcase ventilation system. Same reason taking lots of short trips leads to a gassy smelling dipstick (insert wisecrack here).

 

[TakaraLC]

Is it possible that air was so cold that the engine oil never got hot enough for the fuel to fully evaporate and go out the crankcase? To my idiot level of understanding some amount of blow-by is pretty much inevitable which is why running a warm engine for a certain amount of time is needed for that sneaky fuel to vaporize and be removed through the crankcase ventilation system. Same reason taking lots of short trips leads to a gassy smelling dipstick (insert wisecrack here).

Yes if the oil heats up to operating temperature for an extended period of time gas will evaporate and gets vented.

 

[uraniumrich]

Yes if the oil heats up to operating temperature for an extended period of time gas will evaporate and gets vented.

The oil was taken after a 6 hour drive/400 miles. So, it was up to operating temperature for some time. I don't think this is the source of the dilution.

 

[uraniumrich]

I am NOT an expert on this subject matter.

Both oil analysis’ that I have done (SPEEDiagnostix) had small amounts of gasoline in it. The second oil change had slightly more.

This does concern me for potentially shortening the life of Miss Daisy.

Can you share the details of your analysis?

 

[Bad1975]

Excessive idling (warming up the vehicle while parked) will cause excess fuel in the oil if done allot. Any excessive idling will cause this, I mention warmup because the LC should shut down the ICE when warmed up while driving in stop and go traffic, unless of course your using tow/haul to defeat the ICE shutting down.

Idling when already warmed up is not as bad as the system is no longer running in open loop. When cold its in open loop and as such will run on the rich side to be safe causing unburnt fuel to be present.

 

[ultane]

Can you share the details of your analysis?

When I find them again, if I can find this thread again.

 

[LCOceans]

Excessive idling (warming up the vehicle while parked) will cause excess fuel in the oil if done allot. Any excessive idling will cause this, I mention warmup because the LC should shut down the ICE when warmed up while driving in stop and go traffic, unless of course your using tow/haul to defeat the ICE shutting down.

Idling when already warmed up is not as bad as the system is no longer running in open loop. When cold its in open loop and as such will run on the rich side to be safe causing unburnt fuel to be present.

Very informative and interesting. So I should not idle so long on these cold winter starts as I have been doing before I pull out of driveway.

 

[EOD Guy]

My entire life I thought gas in the oil was caused by unburnt miniscule particles of getting trapped by the top ring and blowing by the 2nd ring and the oil ring on the next compression stroke. Blow by in most cases is due to ring gap and/or cylinder wall condition.

 

[jbe2289]

I’m not an expert by any means, and I could be totally wrong on this. But with the hybrid system, it is my understanding that wash down is a problem: gas being injected into the combustion chamber, but not being burned off because it switches to electric. This washes the oil away from the pistons causing wear and it also lets gas run directly into the oil then. For instance, when you pull in your driveway, the engine shuts off and might have gas injected in that is never burned off. I’ve done two oil changes so far, the first at 1,000 miles smelled strongly of gas and had a sheen on top, in addition to looking like coffee and a glitter bomb. The second oil change at 5,000 miles had no gas smell and was relatively clean, but darker brown in color. Didn’t get an analysis done. This is why it is important to use a high quality synthetic oil and regular changes on a hybrid.

 

[ultane]

Can you share the details of your analysis?

The fuel dilution went from 1.56 at 1200 mile oil change, to 2.56 at the 4500 mile oil change. I changed the oil and filter at 4500 miles since we were going out of town and wouldn’t be back until the odometer was at ~6,000 miles.

I do not know what the ‘units’ are for ‘fuel dilution’.

 

[EOD Guy]

The fuel dilution went from 1.56 at 1200 mile oil change, to 2.56 at the 4500 mile oil change. I changed the oil and filter at 4500 miles since we were going out of town and wouldn’t be back until the odometer was at ~6,000 miles.

I do not know what the ‘units’ are for ‘fuel dilution’.

Not an expert by any stretch of the word........... I believe the measurements are "parts per million" so in your case they increased. Probably still within acceptable parameters, IDK.

 

[Bad1975]

I'll post my UOA here when it comes in. First change at ~2600 miles with no warm ups. Also changed both diffs and xfer case oil, all had metallic paste like muck on the drain plugs, similar in look to Molybdenum grease.

 

[ultane]

Not an expert by any stretch of the word........... I believe the measurements are "parts per million" so in your case they increased. Probably still within acceptable parameters, IDK.

Yes, I think it is within normal range. It just bothers me. I will definitely keep an eye on it.

 

[jbe2289]

I'll post my UOA here when it comes in. First change at ~2600 miles with no warm ups. Also changed both diffs and xfer case oil, all had metallic paste like muck on the drain plugs, similar in look to Molybdenum grease.

Sounds pretty normal, and why they use magnetic drain plugs in there. Lots of wear in. I changed the differential, transfer, and manual transmission fluid in both of my Tacomas at around 10,000 miles. All except the 2020 Tacoma rear differential didn’t need changed and the fluid looked new, but yes lots of metal particle paste on the plugs. But the 2020 rear differential was contaminated with water, the fluid was milky white and stunk terrible. Not sure if I’m going to change the Land Cruiser early or not. The transmission interests me most, but seems like a real pain, never changed an automatic before.

 

[EOD Guy]

Sounds pretty normal, and why they use magnetic drain plugs in there. Lots of wear in. I changed the differential, transfer, and manual transmission fluid in both of my Tacomas at around 10,000 miles. All except the 2020 Tacoma rear differential didn’t need changed and the fluid looked new, but yes lots of metal particle paste on the plugs. But the 2020 rear differential was contaminated with water, the fluid was milky white and stunk terrible. Not sure if I’m going to change the Land Cruiser early or not. The transmission interests me most, but seems like a real pain, never changed an automatic before.

I'm going to have the dealer change my Xmsn fluid at 10K, probably wouldn't need to but in my way of thinking, any initial wear items will have worn and I want to get it flushed out and clean stuff in.

 

[Bad1975]

I'm going to have the dealer change my Xmsn fluid at 10K, probably wouldn't need to but in my way of thinking, any initial wear items will have worn and I want to get it flushed out and clean stuff in.

I don't screw with automatics and follow the manufacturer recommendations unless they specify lifetime, I'll probably wait until 60k or maybe even 100k. Not sure what Toyota recommends for it as I haven't looked yet?

It's hard to get a complete fluid change on an auto unless you do a flush or buy 3-4 times the amount of fluid and run it through on multiple changes back to back.

Toyotas procedure has 4 Qts. for drain and fill and the transmission system as a whole contains 8 Qts. Getting the filter changed along with the drain and fill would be ideal. I didn't see the filter change in TIS anywhere though when I was in there last, the procedure is the same on the Tundra minus the temperature method is different due to older electronics and there is no thermal degradation counter like the LC250 has. I need to make a few changes in GTS+ to mine shortly so I will look for a trans filter procedure again while I have an active subscription.

I bought on of these to make transmission, xfer and differential fluid changes easy and clean and also use it at work occasionally, support Toyota and allot of European brands with direct thread adapters and has universal for anything else:
https://www.amazon.com/Private-PBT71197-QuickFlow-Transmission-Service/dp/B08HSJFZT5


I just did my Tundra with 130k on the clock with about 20k of that towing and about 5k of that offroad and the fluid still was fine (red/slightly darker tint) and not allot of clutch disc material present but enough to lightly coat the pan and tint the fluid and no burnt smell to it.

On our Volvo you can flush by running a fill line and the return through one of the heat exchangers, can't change the filter without engine removal so the flush was allot more important on it and fluid looked the same as Tundra at 120k.

 

[uraniumrich]

Excessive idling (warming up the vehicle while parked) will cause excess fuel in the oil if done allot. Any excessive idling will cause this, I mention warmup because the LC should shut down the ICE when warmed up while driving in stop and go traffic, unless of course your using tow/haul to defeat the ICE shutting down.

Idling when already warmed up is not as bad as the system is no longer running in open loop. When cold its in open loop and as such will run on the rich side to be safe causing unburnt fuel to be present.

I don't have excessive idling on my LC at all. Even when it sits outside and it's cold, I start it up, let the oil pressure build, and then get it moving. The best way to warm up the engine is to get the vehicle in motion, not let it sit and warm up. At least in my case, this isn't the reason for the fuel dilution.

 

[uraniumrich]

I don't screw with automatics and follow the manufacturer recommendations unless they specify lifetime, I'll probably wait until 60k or maybe even 100k. Not sure what Toyota recommends for it as I haven't looked yet?

It's hard to get a complete fluid change on an auto unless you do a flush or buy 3-4 times the amount of fluid and run it through on multiple changes back to back.

Toyotas procedure has 4 Qts. for drain and fill and the transmission system as a whole contains 8 Qts. Getting the filter changed along with the drain and fill would be ideal. I didn't see the filter change in TIS anywhere though when I was in there last, the procedure is the same on the Tundra minus the temperature method is different due to older electronics and there is no thermal degradation counter like the LC250 has. I need to make a few changes in GTS+ to mine shortly so I will look for a trans filter procedure again while I have an active subscription.

I bought on of these to make transmission, xfer and differential fluid changes easy and clean and also use it at work occasionally, support Toyota and allot of European brands with direct thread adapters and has universal for anything else:
https://www.amazon.com/Private-PBT71197-QuickFlow-Transmission-Service/dp/B08HSJFZT5


I just did my Tundra with 130k on the clock with about 20k of that towing and about 5k of that offroad and the fluid still was fine (red/slightly darker tint) and not allot of clutch disc material present but enough to lightly coat the pan and tint the fluid and no burnt smell to it.

On our Volvo you can flush by running a fill line and the return through one of the heat exchangers, can't change the filter without engine removal so the flush was allot more important on it and fluid looked the same as Tundra at 120k.

Lifetime fluid is a myth. Well, unless they mean that you can shorten the lifetime of your transmission by never changing the fluid. I am curious to know if the drain and fill is an effective way to prolong the life of your transmission. Most of the stuff I've read/watched about transmission fluid suggests that as the clutch wears, it's not a great idea to completely change the fluid (because the clutch may begin to slip with fluid that has zero clutch particles in it.) On my RDX, I do a drain and fill on the transmission fluid and transfer case every 30K miles and the rear differential every 15K miles. If I recall correctly, the transmission fluid has a small filter that is on the cooler and is easily replaceable.