: fuel dilution issues with DI engine?

04-12-09, 09:16 AM
As the DI engine becomes more popular there seems to be correspondingly more and more discussion re fuel dilution issues with these same DI engines. From some of the Used Oil Analyses I have seen over on BITOG these GM (DI) VVT 3.6 L engines are very hard on oil. This is my first visit to cadillacforums. I am wondering if this has already been discussed in detail? Elsewhere there is some thought that the choice of oil can help in combating the effects of excessive fuel dilution. Based upon any UOAs that might have been posted here is there a consensus re a 'best' oil? Thanks for your advice.

04-19-09, 07:44 PM
This is an issue with all DI vehicles. DI vehicles are meant to run very very lean.

The problem is for protection they tend to run rich like a port fuel vehicle top end and you get cylinder wash.

Tune the vehicle with HPtuners, and use Royal Purple every 4000-5000 miles.

04-19-09, 09:17 PM
This is an issue with all DI vehicles. DI vehicles are meant to run very very lean.

use Royal Purple every 4000-5000 miles.

I thought I would see some Used Oil Analyses for this DI engine...but I dont see any. That is the only way to judge how protecting the oil really is.

Are there any UOAs on cadillacforums?

04-20-09, 06:34 AM
Can I assume, you mean 'oil dilution' due to fuel. I would think that if your valves and rings were seating properly this would be minimal in impact. After all, even with increased pressure of fuel delivery, combustion pressures are greatly higher than injection pressures. I could see that DI would be more prone to oil dilution if the vehicle involved was used in a lot of short trip scenarios and the fuel that gets into the oil (during startup and warmup) didn't get a chance to be burned when the oil gets up to operationg temperatures. Short trip cycles are hard on any engine regardless of injection type.