Oil/Fuel Dilution Concerns...

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[32spoke]

There's lots to unpack here. I'll chime in on what I can help with.

It's expected that your oil will be thin, have fuel contamination, and metallic content during the first say 1600km (1000m). I'm not surprised at all. This is when most of the wear your engine will ever see occurs. During the break-in period.

Fuel dilution will increase as the temperature decreases. This is due to a number of factors, which I may go into more detail on in a future thread. They are: slower vaporization rate of gasoline as it enters the cylinder, thermal deformation of pistons relative to cylinders, and the time it takes to engine oil to reach operating temperature (80-100C). Some people may have no issues at all with fuel dilution if they live in a warm climate.

Viscosity shearing is not what's negatively affecting your oil. Shearing is where the viscosity modifiers (very specialized chemistry that is designed to increase the viscosity of the oil as it gets hotter) are physically SHEARED and no longer can perform their function. These molecules actual unwind and take up more space as they get hot. They prevent to oil from thinning out too much as it warms up. Timing chains are a big source of shear wear. If you're concerned about shear wear look at the HTHS (high temp/high shear) testing values for given oils.

One must be careful using a grade of oil other than what is specified for the engine. if you want to try it (and I will be in the future), I suggest focusing on the winter grade value (the "W" part of the viscosity range. Fuel dilution is really only an issue when the engine is below operating temperature. This has very little to do with coolant temperature an everything to do with oil temperature. Just because your coolant is at 80C, doesn't mean your oil is. In fact, in my test, oil temp takes quite a long time to reach 80C and above, and requires a fair bit of time (say 30 minutes) or considerable load on the engine. I may get into why 80C is the magic number in a future thread if anyone is keen. But the W number is important. Toyota likely runs 0W oil fortwo reasons: 1) to ensure the engine starts easily in VERY cold weather (think -45C) and 2) to improve corporate average fuel efficiency numbers. Going down the grade scale by one grade can increase fuel efficiency by between 0.2% and 0.4% which seems like a small amount, but in an ICE engine that is likely only 40% efficient, it's a huge deal.

Back to why focus on the W aspect of the multiviscosity oil...

Firstly, fuel dilution is MUCH worse at low temps so that's the end of the scale we want to modify. Secondly, if you go up a grade you're exposing the oil to a viscosity range that it already sees within the manufacturer recommended oil. Meaning, 0W-20 "contains a range of grades, between 0 and 20. So introducing say a 5 weight oil isn't an issue. It won't offer more protection to fuel dilution. That comes from chemicals in the oil called dispersants. Any oil with API-SP rating will have a butt load of dispersants. It may REDUCE fuel dilution because it will form a stronger film between cylinder bore and piston rings when the engine is cold as compared to 0W. When an engine is cold, the parts don't fit together properly. They all have clearance values determined by the engineers, and those clearances are wider when the engine is cold. All metals expand (albeit at different rates) when they warm and the engine is designed to run at operating temp (80C+). A 5W oil will provide strong er film strength at startup and may reduce fuel dilution as a consequence. 5W is rated for-40C (this spec published in SAE J300 if you want to look it up) and 0W is rated to -45C. So unless you live somewhere REALLY cold, 5W-20 should be fine. Even the owners manual says you can run it (but you should change it back to 0W-20 when you can).

If you go up to XW-30, you're introducing an oil viscosity range that the engine wasn't designed for. Remember those clearances I talked about? They could be too tight to allow adequate film formation with your 30 weight oil in some journals or bearing surfaces. I suggest you steer clear of increasing that end of the range.

Sorry for rambling on, but I hope this helps you work out your plan of action.

Toyota recommends 5w30 for the T24A-FTS in non North American applications.. which undermines your comment about xw-30 oil viscosity. 0w20 oil is used to bump up mileage for improved CAFE ratings, which is why Toyota recommends this oil- yet Toyota even recommends a 10w30 oil as well for this engine, though obviously not suggested for cold weather.
https://toyota-club.net/files/techdata/ttx/lc_250g.htm#:~:text=Toyota-Club.Net - Fluids,Brakes

https://bobistheoilguy.com/forums/threads/t24-a-fts-turbo-engine.400187/

 

[izzy]

Toyota recommends 5w30 for the T24A-FTS in non North American applications.. which undermines your comment about xw-30 oil viscosity. 0w20 oil is used to bump up mileage for improved CAFE ratings, which is why Toyota recommends this oil- yet Toyota even recommends a 10w30 oil as well for this engine, though obviously not suggested for cold weather.
https://toyota-club.net/files/techdata/ttx/lc_250g.htm#:~:text=Toyota-Club.Net - Fluids,Brakes

https://bobistheoilguy.com/forums/threads/t24-a-fts-turbo-engine.400187/

As soon as my warranty is up I'm gonna switch to 5w30.

No way I'm doing that while it's still in warranty.

If your engine fails, I guarantee they will go Sherlock Holmes mode on your ass and if your oil isn't to spec you're toast.

 

[32spoke]

As soon as my warranty is up I'm gonna switch to 5w30.

No way I'm doing that while it's still in warranty.

If your engine fails, I guarantee they will go Sherlock Holmes mode on your ass and if your oil isn't to spec you're toast.

Since Toyota recommends the other oil viscosities, one could remind them of this, and
During arbitration, it would be introduced. My risk, my concern, my informed opinion backed
By Toyota’s European recommendation.

 

[Franko Manini]

Toyota recommends 5w30 for the T24A-FTS in non North American applications.. which undermines your comment about xw-30 oil viscosity. 0w20 oil is used to bump up mileage for improved CAFE ratings, which is why Toyota recommends this oil- yet Toyota even recommends a 10w30 oil as well for this engine, though obviously not suggested for cold weather.
https://toyota-club.net/files/techdata/ttx/lc_250g.htm#:~:text=Toyota-Club.Net - Fluids,Brakes

https://bobistheoilguy.com/forums/threads/t24-a-fts-turbo-engine.400187/

32spoke, you're 100% correct. I had not come across the oil specifications for markets outside North America, and it makes complete sense. CAFE standards don't apply outside NA (I'm not even sure they really apply in Canada, but our market is so small compared to the US, we just get lumped in I think), and there are plenty of markets that don't see the kind of winter weather we can get in NA. Both point to the ability to run higher viscosity engine oil - in those environments. I would really avoid running 10W-30 in a cold climate in this engine. But it appears that it will absolutely tolerate a XXW-30 oil.

My plan is to first try 5W-20, and if that doesn't help my oil dilution issue, I may go to 5W-30, but honestly, I think it's the winter grade number that will influence the dilution issue the most.

Good catch, and thanks for the additional information.

 

[32spoke]

32spoke, you're 100% correct. I had not come across the oil specifications for markets outside North America, and it makes complete sense. CAFE standards don't apply outside NA (I'm not even sure they really apply in Canada, but our market is so small compared to the US, we just get lumped in I think), and there are plenty of markets that don't see the kind of winter weather we can get in NA. Both point to the ability to run higher viscosity engine oil - in those environments. I would really avoid running 10W-30 in a cold climate in this engine. But it appears that it will absolutely tolerate a XXW-30 oil.

My plan is to first try 5W-20, and if that doesn't help my oil dilution issue, I may go to 5W-30, but honestly, I think it's the winter grade number that will influence the dilution issue the most.

Good catch, and thanks for the additional information.

No worries, enjoy your truck and thank you for your kind reply. When the dealer advised me of their 10k mile oil changes, I walked out and went to the shop next to my store and asked them to change the oil. I have it changed every 5k miles as I know that oil filters aren’t known for filtering out liquid contaminants such as condensation from cold starts, and to your point- fuel contamination.

 

[izzy]

No worries, enjoy your truck and thank you for your kind reply. When the dealer advised me of their 10k mile oil changes, I walked out and went to the shop next to my store and asked them to change the oil. I have it changed every 5k miles as I know that oil filters aren’t known for filtering out liquid contaminants such as condensation from cold starts, and to your point- fuel contamination.

You can also just have the dealer do 5k intervals.. by just telling them to change the oil lol they won't refuse.

This will be an interesting experiment, since I'll be on 0w20 until 125,000 miles at 5k intervals.

Maybe I'll have my shop take a borescope of the cylinders at the last 0w20 change. I'll follow up in 5-7 years or however long it takes me to hit 125,000 miles.

 

[32spoke]

You can also just have the dealer do 5k intervals.. by just telling them to change the oil lol they won't refuse.

This will be an interesting experiment, since I'll be on 0w20 until 125,000 miles at 5k intervals.

Maybe I'll have my shop take a borescope of the cylinders at the last 0w20 change. I'll follow up in 5-7 years or however long it takes me to hit 125,000 miles.

Boroscope might show cylinder wall damage or a head gasket failure or crack in the cylinder head… but PPM of wear metals from an oil lab would be the best indicator of abnormal/accelerated wear.. GM just switch out a OW20 for their super care mobil1 dexos spec 0W40 to protect some of their 6.2 liter engines. Oil changes must be free if required by the dealership/magnusson moss act.. I have the repair shop next to my store do the oil changes.. I know the person changing the oil, peace of mind

 

[izzy]

Boroscope might show cylinder wall damage or a head gasket failure or crack in the cylinder head… but PPM of wear metals from an oil lab would be the best indicator of abnormal/accelerated wear.. GM just switch out a OW20 for their super care mobil1 dexos spec 0W40 to protect some of their 6.2 liter engines. Oil changes must be free if required by the dealership/magnusson moss act.. I have the repair shop next to my store do the oil changes.. I know the person changing the oil, peace of mind

Pretty sure GM did that switch (which they then reversed) because they can't machine a bottom end properly lol

I'm not thin oil defender, I run 5w40 in my WRX, I know oil.

I think what is far more important, is the OCI. 0w20, if it's quality oil, will not degrade to the point of damaging bearing surfaces, rings, or cylinder walls in 5,000 miles.

10,000 mile intervals will definitely wear 0w to the point the viscosity is so thin you may see increased wear. Both GM and Toyota are now on "once a year/10,000 mile OCI" which is way too long.

5,000 mile or less OCI is key, which everyone here agrees with.

 

[MustardTiger]

Question for Grok: For a 0w20 viscosity engine oil, at a 6 quart quantity…if 5% gasoline is added to that 6 quarts…how would the viscosity of that engine oil change or be effected?

Answer from Grok:

When you contaminate a 0W-20 fully synthetic engine oil with 5% gasoline (in your case, ~9.5 oz or ~280 ml of gasoline mixed into 6 quarts of oil), the viscosity changes significantly, and almost entirely in the wrong direction for engine protection.

Here’s what happens in detail:

1. Cold-temperature viscosity (the “0W” part)

• Pure 0W-20 typically has a kinematic viscosity at −35°C of around 5,500–6,500 mPa·s (cP).
• Gasoline is extremely thin at cold temperatures (~0.4–0.6 cP).
• Even 5% gasoline dilution drops the cold cranking viscosity dramatically — often by 20–40%.
• Result: The oil still easily meets 0W requirements (the limit is 6,200 cP at −35°C), so cold-start pumping and flow actually improves slightly. This part is not the problem.

2. Hot-temperature viscosity (the “20” part) — THIS IS THE BIG PROBLEM

• A good 0W-20 has a kinematic viscosity at 100°C of ~8.2–9.5 cSt (typically right around 8.5–9.0 cSt for most modern synthetics).
• Gasoline at 100°C has a kinematic viscosity of roughly 0.3–0.4 cSt.
• 5% gasoline dilution typically drops the 100°C viscosity by ~15–25%.

Real-world measurements from oil analysis labs and OEM studies show:

Gasoline Dilution	Approx. 100°C Viscosity of a typical 0W-20
0% (clean)	8.5–9.0 cSt
5%	6.8–7.6 cSt
7–8%	Can fall below 6.5 cSt (into 5W-16 / 5W-12 territory)

At 5% dilution:

• The oil is no longer an SAE 20-grade at operating temperature.
• It behaves more like an SAE 15 or low SAE 16 — dangerously thin for engines designed and calibrated for 0W-20.
• High-pressure oil films in bearings, piston rings, and especially variable valve timing (VVT) actuators and cam phasers become much thinner → increased wear and risk of metal-to-metal contact.

3. Other negative effects of 5% gasoline dilution

• Lower flash point → higher risk of oil burning or fire in crankcase
• Faster oxidation and acidity increase
• Washes oil film off cylinder walls → accelerated ring and bore wear
• Can cause hydraulic lifter/tappet and chain tensioner problems (they collapse or pump up incorrectly with thinner oil)
• Increased fuel consumption and oil consumption

OEM condemnation limits

Most manufacturers (Toyota, Honda, Ford, GM, etc.) consider >4–5% fuel dilution as condemnable in 0W-20 engines. Many set the alarm limit at 3–4% and require oil change at 5–6%.

Bottom line for your scenario

Adding 5% gasoline to 6 quarts of 0W-20 will:

• Drop hot viscosity roughly 1.0–2.0 cSt at 100°C (from ~8.7 cSt → ~7.0–7.5 cSt)
• Push the oil outside the SAE 20 grade at operating temperature
• Substantially increase engine wear, especially in rod/main bearings and camshaft areas
• Likely trigger check-engine lights in vehicles with sophisticated oil-life monitors or dilution sensors (many late-model Toyotas, Hondas, and Fords)

In short: 5% gasoline dilution is very bad for a modern 0W-20 engine. It turns a perfectly good oil into something closer to a 0W-16 or thinner, which the engine was never designed to run. Change the oil immediately if you ever see 5% or higher fuel dilution on a used oil analysis.

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