Fuel dilution - 1.9 mile commute. Let idle before leaving?

[So1911]

I have an NB2 Miata. My commute is 2 miles each way.. My oil reports (blackstone) are coming back with somewhat high (correction, low, 375f and 420f on two samples) flashpoints. I understand that there is debate about the reliability of blackstone's flashpoint for fuel dilution, but my question is more, what is best practice for starting the car in the morning? Typically with any car I let it idle 30-45 seconds, drive easy until oil is warm (about 5 minutes after coolant is up to temp).

But, with such a short commute, there is no way my oil is getting to temp. Should I let it idle longer in the mornings? Take a longer route to work?

 

[JavierH19]

I wouldn't bother idling unless it's extremely cold, I normally let my engines idle just for a few seconds so they fully build oil pressure and that's all. I wouldn't bother trying to do anything special either, just drive it normally. And trying to warm the oil more by idling more would likely just make it worse.

As for the fuel dilution I'd normally suggest something a bit thicker with less vii like 15w-40 since that engine calls for 5/10w-30. It has less polymers to break down from the fuel and a bit more viscosity to combat it. But because that oil doesn't really heat up I'd just use a cheap syn blend 10w-30 instead of 5w-30 and change more frequently. A half year interval is what I'd do if i had that driving style. I'm sure you have some kind of longish drive at least once a month that's a half hour in length. That's enough to flash some fuel off but it's not that necessary.

 

[dadto2]

I suspect letting is idle longer in the morning will only increase the fuel dilution. Get it out on the open road on the weekends for 30-40 mile trips at speed, that's the only way to get the oil hot enough for long enough to flash off the fuel. I think you should follow a shorter oil change interval to be honest.

 

[Kira]

We've seen posts of similar predicaments before.
All the data from studies of fleet vehicles-fuel dilution-short hopping are too much to digest here.
The bottom line in the "<3 mile category" is....never shut your vehicle off.

 

[kschachn]

I have an NB2 Miata. My commute is 2 miles each way.. My oil reports (blackstone) are coming back with somewhat high flashpoints. I understand that there is debate about the reliability, but my question is more, what is best practice for starting the car in the morning? Typically with any car I let it idle 30-45 seconds, drive easy until oil is warm (about 5 minutes after coolant is up to temp).

High flash points?

 

[demarpaint]

Idling it is going to do more harm than good. Take it for a ride for about 25-30 minutes twice a month instead.

 

[Brian123]

High flash points?

I am thinking he should have said Low! Unless the OP thinks anything above a certain number is High when it is really Low.

 

[So1911]

Yes sorry low flashpoints. One was 375f and the other UOA came back with 420f

 

[So1911]

I suspect letting is idle longer in the morning will only increase the fuel dilution. Get it out on the open road on the weekends for 30-40 mile trips at speed, that's the only way to get the oil hot enough for long enough to flash off the fuel. I think you should follow a shorter oil change interval to be honest.

Good to know. I get it up to temp and wind it out at least every couple days, if not every day, but my thought process it I know it runs very, very rich on cold map. So it sounds like the general suggestion is, don't worry about getting it to hit rich map on the commute. Just every now and then get it up to operating temp

 

[kschachn]

Yes sorry low flashpoints. One was 375f and the other UOA came back with 420f

Using flash point to estimate fuel dilution is an inferior method. I am not sure if I would believe any of that without confirming with a different method. Blackstone dilution numbers have been shown to be sometimes wildly inaccurate.

 

[Chris142]

Idling a cold engine will put more fuel into the oil.

 

[thunderous1335]

Walk, bike, or get an electric car.

 

[So1911]

Walk, bike, or get an electric car.

I have a Model S. Prefer the Miata

 

[PimTac]

I have a Model S. Prefer the Miata

Then you will have to live with fuel dilution. There is no answer other than to drive it more.

 

[IndyIan]

Get a block or coolant heater and plug it in. I don't know how hot those go but you'll cut down your warm up time quite a bit.

 

[LeoStrop]

Idling with a cold engine will only improve the fuel dilution. With only a short commute, your oil won't be hot enough to justify letting it idle when you reach your destination either.

There is no other way around it, other than driving for longer distances, or forget about it and follow shorter OCI.

 

[Shel_B]

Then you will have to live with fuel dilution. There is no answer other than to drive it more.

I make a lot of short tips every week. I generally drive in a lower gear (2nd or 3rd) and often take the long route home. I think that may help somewhat. Regardless, I do try to get out on the road several times a month for a long trip. I also keep the OCIs short.

 

[chris719]

I have a Model S. Prefer the Miata

Just drive the Miata. It's a reliable engine. If it dies then LS swap or MZR 2.5 swap. Just try to run errands with it that are a longer trip as much as possible.

 

[ATex7239]

I suspect letting is idle longer in the morning will only increase the fuel dilution. Get it out on the open road on the weekends for 30-40 mile trips at speed, that's the only way to get the oil hot enough for long enough to flash off the fuel. I think you should follow a shorter oil change interval to be honest.

Does the common suggestion to drive for longer to “get rid” of fuel in oil have any merit?

I don’t think we’d see so many diluted samples if it did. Operating temp of oil averages 200-250F and the flash point of fuel is basically double that. I think once it is in there it is pretty much gonna stay unless you change the oil.

 

[ATex7239]

Change the oil more frequently is what I would don in this situation. I’m not one to alter my day to suit a machine.