GDI vs. MPFI OCI's

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A number of threads have posts saying GDI engines need shorter OCI's than MPFI engines.

Why?

I asked within those post, without a reply I could find. Couldn't find topic in searched posts, either. I own GDI, MPFI, and carbureted gasoline engines, along with various 2 strokes. Getting quite confusing to me.
 
GDI engines produce more soot than MPFI engines also in many gdi engines the injectors end up spraying small amounts of liquid fuel onto the cylinder walls which ends up in the crankcase resulting in higher rates of fuel dilution than MPFI engines..
 
Gasoline Contamination of the Oil and Soot

Under certain conditions the extremely high injection pressures is forcing fuel past the rings. This may result in accelerated wear of parts like timing sets.

GDI forms soot similar to direct injection diesels. It's hard on certain internal parts such as timing sets.

Now are the recommended intervals to long? It's hard to say. We do know we have been seeing timing set failures. How much is a design issue vs fuel contamination or soot loading remains to be proven.

We do know that it's important enough that one of the driver's of the new GF-6 Standard was to reduce timing set wear.
 
I'm doing 3k on my mazda DI, especially in cooler weather.
Fuel dilution in cool weather.
 
Last edited:
Originally Posted by Propflux01
What would one consider a "shorter interval"? Most vehicles have either a set parameter such as 7500 miles, or a oil change monitoring system.

Hyundai which is known for having some of the sootiest fuel diluting GDI engines recommends a 3750mi interval on their GDI engines and 3000 on their TGDI engines when used in severe service which is pretty much most driving conditions unless all you ever do is drive on the highway.
 
Originally Posted by Propflux01
All Hyundai engines have the 3750 SS intervals (sans turbo, of course). I change mine at 5000 OCI, in between SS and NS mileage.

That's what I've done on any HyunKia. The recommendations aren't a two position switch, they're a dial with both extremes at the stop point. Divide by five is easy to remember.
 
Originally Posted by spasm3
I'm doing 3k on my mazda DI, especially in cooler weather.
Fuel dilution in cool weather.


Good decision. I do 6 months or 5K whichever comes first on my Golf.
My manual says 10,000 miles or 1 year under normal conditions.

When they say normal condition it actually means ideal condition where oil reaches operating temperature of at least 212°F at which point moisture and other contaminants start to boil off or evaporate. How many of us are in that crowd? Not many.

Quite some time ago I remember reading a research paper presented by Association of Oil Filter Manufacturers and they concluded that majority of us (over 80%) drive under severe driving conditions and suggested to cut OCI in half or more.
 
Regarding DI engines, I like all the 3K to 3.75K OCI answers out there. Good job.
 
Originally Posted by Propflux01
I've done two Blackstone samples on the GT, and both have come out great.Both sampled at approx 5K intervals

Like the looks on that GT. Had one as a rental and it seemed pleasant.
 
Originally Posted by SteveG4
Regarding DI engines, I like all the 3K to 3.75K OCI answers out there. Good job.


5K should be ok if you don't drive hard and don't have tune like some do. But yes, 3 K is even better.
 
Originally Posted by Propflux01
I've done two Blackstone samples on the GT, and both have come out great.Both sampled at approx 5K intervals


Good to know and it's helpful to see how the additive package performed and what the depletion rate was.

But what's actually more important to know is how that oil performed in preventing wear which is done by wear protection test and results are stated in PSI values and standard UOA won't tell you that.
 
I bought a new Mazdaspeed 3 in July 2007 and drove it 158K miles before flipping it for my 2er(another GDI turbo). UOAs established that a 7.5K mile OCI using M1 5W-30 was-if anything-conservative. I stuck to that interval as it lined up with other maintenance items.
 
Wow - thanks for all the info.

I suspected fuel dilution was the answer, but wasn't sure since gasoline is much more volatile than diesel fuel. This seems akin to biodiesel reduced OCI (I own gas & diesel engines, and we are forced to buy only biodiesel - which is ok except for the short storage life and higher gel temp).

I assume gasoline has an injection pressure limit due to safety reasons, therefore can't get better atomization to prevent fuel dilution and unburned HC's in the oil? Why would engine makers go with GDI instead of MPFI, if MPFI provides more complete combustion?
 
Originally Posted by LubricatusObsess
Wow - thanks for all the info.

I suspected fuel dilution was the answer, but wasn't sure since gasoline is much more volatile than diesel fuel. This seems akin to biodiesel reduced OCI (I own gas & diesel engines, and we are forced to buy only biodiesel - which is ok except for the short storage life and higher gel temp).

I assume gasoline has an injection pressure limit due to safety reasons, therefore can't get better atomization to prevent fuel dilution and unburned HC's in the oil? Why would engine makers go with GDI instead of MPFI, if MPFI provides more complete combustion?


This is why: This is the Elantra GT GDI's piston top after I did a scope last week. The engine has 85K on it.

Piston.JPG
 
Can't get my scope in there far enough. But notwithstanding, the lack of carbon deposits is usually a good indicator of complete combustion. My MPI engine in my Elantra has deposits.
 
It's where deposits seem to happen. On the intake valves. .

At least the tops are sparkling clean
lol.gif
 
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