How hot does an engine need to get to eliminate fuel dilution?

[theorist]

Does anyone know at what engine or oil temperature gasoline (regular winter gasoline) will boil or quickly evaporate out of motor oil, quickly reducing fuel dilution?

My 2012 Mazda 3 with a direct injection Skyactiv engine runs a bit cold. In the winter its coolant temperature rarely exceeds 81°C or 178°F and takes about 10 minutes to reach 170°F. If I use the cabin heater as I'd like to or drive trips of less than 15 minutes as I often do, the coolant rarely exceeds 170°F according to my ScanGauge. (Unfortunately I cannot read the oil temperature.) These engines, like many direct injection engines, are known for fuel dilution. While the car was under warranty I asked a couple dealers to replace the thermostat, but they insisted that is as long as it's not throwing an OBD code it's not a problem. Some winters I've used a partial grille block which had really helped. I'm thinking of replacing the thermostat now, hoping that will bring the coolant up to the specified 85°C or 185°F in the winter, like it does in the summer.

How important is this for the health and longevity of the oil, especially with maybe 20 short 5-12 minute trips and maybe 2-4 longer 15 to 40 minute trips?

 

[Shannow]

You can't eliminate it.

There will always be a residual.

These might help with the concept

 

[theorist]

BTW, the car has a bit more that 100kmiles and runs great. The car doesn't burn more that a few ounces of oil between oil changes (unless it's perfectly offset by fuel dilution.)

I've used 0w-20 Castrol Edge, Mobil 1, Pennzoil Platinum, and Castrol Magnatec according to the deals I find with 5-7kmiles between oil and filter changes in case that makes a difference. Recently I look for Dexos1gen2 and SNplus approvals. If there are any other approvals I should look for in a 0w-20 oil let me know. I've considered moving to a 0w-30 or 5w-30 during the warmer half of the year (40° to 90°F). The winters run -10° to 50°F.

 

[theorist]

Originally Posted by Shannow
You can't eliminate it.

There will always be a residual.

These might help with the concept

Thank you. I knew that 'eliminating' it was a gross oversimplification. I'm delighted to find users on BITOG who think more analytically.

I appreciate the graphs but am having some difficulty quickly understanding them. Can you tell me what the Volume% refers to? The volume of what over what? Perhaps the volume of motor oil over the volume of a mix of oil and fuel? The volume going down to 0% confuses me unless it's looking at the equilibrium of a flow of fuel being added to a fixed stock of oil.

 

[Shannow]

They are the distillation curves of fuels.

So take the top curves if you assume that say an ounce of raw fuel made it into the sump, and you got the engine up to 140C oil temperature, 0.2 Oz roughly would still be remaining in the sump.

But the stuff that gets evaporated off is the light, thin stuff that really adversely affects viscosity and protection...the stuff that doesn't evaporate is probably close to what's supposed to be in the sump anyway.

Some of the UOAs on BITOG have me perplexed, as to whether they have only partially warmed the engine to drop the oil and get a sample, as a decent run (or ITalian tuneup) prior to dumping the oil should have eliminated most of the light end of the fuel

 

[DBMaster]

The 30,000 mile UOA I had done on the oil from my 2012 Mazda3 (Skyactiv - I used microGreen filters) indicated the viscosity had actually increased. When I posted that UOA one of the responders stated that was the effect of the fuel dilution/evaporation cycle. Based upon my results with really extended OCIs you shouldn't worry much about the Skyactiv engine ruining its oil prematurely.

The oil used at the time was M1 0W-20 AFE. I have used M1 0W-20 EP for subsequent OCs. EP wasn't available when I started the first 30K OCI.

This is the post.

https://www.bobistheoilguy.com/foru...crogreen-filters-30k-oci-uoa#Post3884300

 

[spk2000]

Those charts are phase diagrams used by engineers and scientists to know what temperatures have what concentrations in them. The charts are telling that that if you reach 140 you are driving off nearly as much as 180

 

[DzoG20]

Very interesting - my skyactiv Mazda 3 is also running colder in the winter and the dealer is skeptical about it, given that there is no OBD code. The car is 2015 and the dealer refuses to believe the thermostat could have an issue. When it is sub-freezing temp outside the coolant temperature never measures over 155-160F during my 20-25min trip (9miles). In the summer it stays at 185F.

My main concern is the valves deposit. The claim is that Mazda controls it with increased temperature on the valves, so the deposit can be baked off. Thus engine running colder worries me somewhat.

 

[Mustangmaster]

Has anybody used any of the new SN Plus formula oils? Wondering if they help with gas in oil dilution. I still have one more oil change to do with leftover Mag1 full synthetic that is the old formula that is not SN Plus. All of their new formulas are SN Plus.

 

[Rolla07]

Are you seeing condensation underneath the oil cap? Thats typically how I judge it. I dont have a DI Mazda but I experience similar issues with not getting temps hot enough as my temp gauge rarely gets up there. I assume you should be able to get it hot enough with a good 15 min highway run. Dont mean to try and oversimplify the issue, as i realize its more complex than this.

 

[BenzFella]

There have been many successful reports of fuel dilution being nearly eliminated in the Honda 1.5T world. Their solution is Castrol Edge 0w40 in the crankcase and 91/93 fuel grade in the gas tank. May be a good option for Mazda as well...

 

[CT8]

Also the oil between the parts is hotter than the oil in the sump.

 

[PimTac]

A good idea is to take that Mazda out for a long drive when you can. Short tripping is hard on any engine.

 

[DoubleWasp]

That's cool running for a modern engine. Most seem to like 195-205°F.

 

[Bryanccfshr]

Here is how I see it. Other than changing your driving behaviors. (Does the car serve you or do you live to serve the car?). If the winter oil gets fuel dilution due to the logistics of your life, just change the oil in the spring when operating temperatures are higher. The time and money you spend on drivesmjust to heat up the engine is equal or more than an additional oil change.
Not everyone's driving habits and use is suitable for year round OCI's. That is why there is a severe service schedule.
If you decide to go visit a relative a few hours away and get a long drive in, that's great, but I wouldn't plan my life around elevating oil temperature. There is the additional risk of accident on winter roads to consider as well,
As a post above stated running a 0w40 may help the oil resist exessive thinning due to fuel dilution. But it may be just as easy to dump in April or May when things warm up for you. Winter is the less than optimal season.

 

[BrianF]

And yes, using a winter front will greatly help retaining coolant heat in the engine and rad. After doing some reading about low coolant temps on my Trailblazer (thermostat was getting lazy) I found that even if the cooler coolant temp does not trigger a CEL, the computer may compensate by running a richer mix in hopes of warming the engine up to proper operating temp.

My Tb was running around that low to mid 80's C. With a new T stat it is high 80's to low 90's C now. I wish I monitored fuel trims to verify the above statement though.

 

[Whimsey]

Originally Posted by Shannow

Some of the UOAs on BITOG have me perplexed, as to whether they have only partially warmed the engine to drop the oil and get a sample, as a decent run (or ITalian tuneup) prior to dumping the oil should have eliminated most of the light end of the fuel


Does it make a difference if you RUN the engine hot on the highway for 30+ minutes and then run it onto ramps immediately and change it or do the same highway run and drive it onto the ramps immediately and change it the next morning without restarting it again? If I'm going to do an oil UOA and the transmission drain and fill I'll use the second method. Thanks.

Whimsey

 

[SonofJoe]

I've never attempted to do the chemical engineering maths on this (they would be horribly complicated!) but my gut feel is that while sump oil temperature IS important, the rate & temperature of the piston blow-by gas flow is equally important in determining the rate at which unburnt/partially burnt gasoline (& water don't forget!) evaporate out of the oil in your sump. Even this doesn't tell the whole story because really it's the ABSOLUTE level of blow-by (ie rate x time) which sets how much gas you ultimately strip out.

If this is correct then if you want to get rid of fuel dilution, first pick a relatively warm day & drive a considerable distance having first loaded up the entire car with bags of sand (or anything heavy!). You're aiming for high engine load to promote hot blow-by, not just revs or speed. Running a car on ramps probably isn't going to cut it load-wise (and will probably annoy your neighbours!).

Oh, and the vagaries of vapour-liquid equilibrium mean that you can never, ever strip all of the gasoline out of oil, once it's in there so don't expect things to be perfect.

 

[theorist]

Thank you! This was the right place to ask! The wealth of engineering knowledge, data, experience, perspectives, and opinions is amazing.

I do an oil change with each seasonal tire change, so one after each winter.

I wouldn't use much of a winter grille block without a ScanGauge displaying actual coolant temperatures. (The ScanGauge can also display the maximum coolant temperature reached that drive, that day, and the day before.) I block most of the larger lower grille with plastic (spare garden edging I had trimmed to fit the grille opening secured with black zip ties) and put a piece of foam pipe insulation in the smaller upper grille slot. The radiator still gets a little cold air flow at speed and can pull more warm air with to the cooling fan when in heavy traffic or driving quickly up a long hill. Still, I've seen coolant temps go just a bit over 100°C if I don't quickly pull out the pipe insulation blocking the top grille. I did this first with my wife's Priuses and now my Mazda3. None of these cars had a real temp gauge. The Mazda3 has a cold engine light that turns off when the coolant reaches 55°C or 131°F. I've never seen either either Prius or the Mazda 3 display an overheating idiot light even with coolant temps going up to 102°C (very rarely.)

 

[theorist]

I read that this skyactiv thermostat is supposed to open at 185 F. I think they try to keep it cooler to avoid preignition with the high compression ratio. I understand that Mazda tried and somewhat succeeded to engineer the engine to keep the intake valves particularly hot, probably partly through running it atkinson mode when the load is light to moderate. Of course atkinson mode would also seem to expose the backside of the intake valves to more deposits.

The only car that I've ever had with condensation on the oil cap was a 93 Saturn SL2 that I bought for 2 grand. My work and my daughter's baby sitter and preschool were only a 15 minute walk from home. My wife didn't want me walking with my daughter in the cold so I bought the Saturn as a second car but drove it two to four times a day just 2-3 minutes at a time. The exhaust rusted out from the inside within 2 years.