It's always discussed about oil temp being necessary to burn off any fuel dilution. It's also generally accepted that you will burn it off in far greater quantities at highway speeds vs idling in park.
Which brings up my question: at idle, my car will run up almost a full 1/4 hotter as far as coolant goes as long as the A/C isn't on. It gets sufficiently hot to actually overfill the reservoir tank when filled to the full cold mark before the auxiliary fans kick on to drop coolant temperature. (For those of you curious, usually within 60-70 seconds from fan on, the reservoir is drained back down to full hot.)
Wouldn't hotter coolant mean an increase in overall motor temp, and raise the temperature of the oil?
Or is there something here I don't understand about coolant and oil temperatures?
Idle vs highway in burning off fuel dilution.
- Thread starter RichardS
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Couple of factors that are additional to that.
Firstly how hot is your oil actually getting ?
Typically you need RPM (and load) to get the oil hot.
Secondly, in order to achieve that aim, you need a good flow of crankcase ventilation to get that happening.
at speed, the oil is getting sprayed around in droplet form, with blowby gasses making it past the rings...plenty of available heat and transport medium to get the vapours to the PCV.
An oil temperature gauge would help. With my old Audi, what you suggested as about temperatures is actually what happened. The coolant (and oil) would get hotter running around in the city (or a lot of idling, too) than on the highway. But, it would take a long time to get there, probably close to an hour of city driving, or 20 minutes of city driving after a good highway run. This vehicle had some peculiarities, too, though, such as an oil cooler that was larger than the coolant radiator.
Generally, idling and low speed running worsens fuel dilution.
From the above, and intuitively, seems like a mixed driving regime would be optimal. Idling to get it hot, then motorway blast to blow it off.
Which is probably what most people do, so everything is for the best in the best of all possible worlds. Maybe.
Another thing to consider is that with modern GDI cars that have anti-knock sensors, then running a higher octane fuel can advance the ignition and reduce the richness of the fuel mixture, which reduces fuel dilution.
heat from the underside of the piston is what really heats the oil. That is from driving down the road. Gasoline is a mix with all different boiling points. Hot oil gets rid of the lighter (lower boiling point)fractions, leaving the heavier fractions. They are only got rid of in an oil change.
My BMW was ridden in commuting service and touring. Every time the first day of a tour the bike used about 4-6 OZ of oil and then never a drop. Once I was due and changed the oil right before a trip, and that time it never used a drop. That 4 to 6 oz was probably fuel dilution burning off. 10KM 6 K mile oil changes.
Rod
Originally Posted By: SR5
Another thing to consider is that with modern GDI cars that have anti-knock sensors, then running a higher octane fuel can advance the ignition and reduce the richness of the fuel mixture, which reduces fuel dilution.
To clarify: I am not trying to address a fuel dilution issue. It was just something that came to mind after the What the FAQ video shared a few hours before my post.
It was just one of those "I wonder" sort of things.
Originally Posted By: SR5
Another thing to consider is that with modern GDI cars that have anti-knock sensors, then running a higher octane fuel can advance the ignition and reduce the richness of the fuel mixture, which reduces fuel dilution.
Just talking out loud here: Even though your coolant/ engine is up to temperature, this does not mean that your oil is up to it's max temp. That said, the longer the drive, the better off you'll be. Highway miles are obviously the more ideal choice here. When does the oil reach it's maximum temperature? Time to install an oil temp sensor if your vehicle doesn't have one.
Also, I've always been under the impression that even though fuel dilution is burned off, the chemistry of the oil is permanently altered. That said, I would try to avoid excess idling or anything else that can lead to unnecessary fuel dilution.
Talking out my rear end hear...but I suspect that the hottest oil in the engine is the oil that's in/coming off the crankshaft and associated bearings.
Even if the coolant temperature is the same or lower, it would seem to me that sustained operation under heavier loads(whether high RPM, or sustained lower RPM cruising) the oil at that point would get a lot hotter than during idle. If nothing else, the oil draining off the crank/bearings should be nice and hot along with having plenty of surface area to evaporate the more volatile components from fuel dilution.
I know that in my one carbureted vehicle, I can often lose a half quart or better in an hour of interstate driving(4 speed without overdrive, so 4th is 1:1. It turns ~4K at 70mph). Beyond that, the only oil loss I can attribute to it is from the increased blow-by from the tired rings and it's about 1 quart per thousand miles.
On the other hand, if I change the oil, get the car halfway to the full mark, and do nothing but short trips I can generally see the oil level rise. It's not huge, but I can certainly see it happening.
I have been running premium (92) Shell in my vehicle after using the fuel provided by the dealer. To date I have not noticed any changes in the oil level on the dipstick nor any smell of fuel. As I do a lot of short trips, 5-15 minutes, it is a big concern for me. At least once a week I get it on the highway for 30 minutes or so just to help burn off anything undesirable. So I am a believer so far in running the higher octane gasoline for this purpose. Even without any scientific backup I recommend it for any GDI or TGDI engine owners.
I wonder if plugging in the car's block heater and using an oil pan heater which speeds up engine warm-up time, would help this situation because it would spend more time in the optimal temperature and less time in between running richer fuel mapping and having the oil trap crank case vapour that can't be burn't off yet.
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Fuel consumption has to be taken into account as well. Steady highway cruising uses the least amount of fuel while maintaining sufficiently high temps. While stop and go or city driving uses a lot more fuel. More fuel burned equals more dilution.
As far as burning off concept, personally I think changing the oil more often is a much better solution than taking long trip with the sole purpose of burning the fuel off.
Originally Posted By: StevieC
I wonder if plugging in the car's block heater and using an oil pan heater which speeds up engine warm-up time, would help this situation because it would spend more time in the optimal temperature and less time in between running richer fuel mapping and having the oil trap crank case vapour that can't be burn't off yet.
Originally Posted By: dlundblad
A block heater certainly would. Anyone know what they warm the coolant to?
On my Scan Gauge it reads 75F with the block heater running for 5 hours before. It's a 400 watt heater according to the information I found online for the 4 Cylinder engine that is in my Journey and 600 watt for the V6 PentaStar engine. It warms to 75F regardless of the outdoor temperature so it has a thermal cut-off.
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