Best Cleaning: DD Or Over Long Trip (FI Cleaner)?

[gathermewool]

I make frequent highway trips that require a fillup when I get home. I usually drive around the speed limit in my turbo Subie to stay off the radar, reduce noise and relax after a long week of work. This may include a few WOT, high-RPM romps, but mostly it's at a steady 65-70 MPH.

Compare this to my daily drive to work, which consists of 25 MPH zones and one very short stint across a bridge where I take the very first exit to work. I drive to work at around 6am, so there's usually minimal traffic. That being said, at least every other day I enter the bridge in third gear and run it WOT all the way up to 5500 RPM before shifting and coasting down the bridge.

I usually, for no real reason, do my every-20kmi-to-30kmi Redline SL-1 add before a long road trip. Any thoughts as to why adding before either might be better? My order should be here by the end of the week, so I'm curious to see what you guys think.

 

[StevieC]

Fuel system cleaning with a highway drive of sorts in the mix is best IMO.

You are good to go with your setup here...

 

[gathermewool]

Good to hear. In my mind, having things up to temperature seemed like the best idea.

The only other thing that stopped me from adding before a week or two of DD'ing is the thought that doing so would cause a larger percentage to go to waste on (not-so) cold starts and idling at lights, especially since I'd more than likely have a larger amount diluting the fuel than on a long highway run. The only portion of my drive that I thought might realize some benefit is the WOT run every other day or so.

 

[StevieC]

I drive a lot for work and I just throw in my cleaner of choice, fill up the tank and then drive until the tank is near empty before refilling.

I do lots of highway but some city driving and never have had problems and only excellent results.

 

[JHZR2]

Time at temperature is good overall, but I like the possibiliy of the adds soaking into deposits time and time again. I like a tank where there are some good intermdiate length (I.e. Enough time to get the engine and oil fully up to temperature so heatsoak is fully complete) drives with a nice longish, hard drive about 3/4 of the way through. This maximizes clock time and time at temp.

 

[gathermewool]

That seems like pretty good advice. If I can, I'll try to use up half a tank before my next long trip and fill up when I get there.

 

[Craig in Canada]

I agree with the concept of a bit of soak, but I'm skeptical just how much of it happens in a modern engine which was brought fully up to temperature...

I'm not sure just how much unburned fuel is sitting around the cylinders or intake valve area after a typical shutdown of an FI engine. My guess would be little to none.

To achieve the desired result I suppose one could always make a habit of starting the car cold and running it for only 5-10 seconds and shutting it down again for a couple of hours. The rich cold startup program may leave fuel vapours around in the system to "soak" as intended.

Where do I get the idea? I know that my engine (BMW M52) does not like to be briefly started, restarted and then left when cold. We call this the "car wash syndrome". If you start your car cold to back it out of the garage, shut down, wash it, start it and pull it in, then let it sit hours/overnight it'll run REALLY poorly the next day for a minute. My inline six sounds like it's running on about three cylinders when this happens. It clears quickly, but is repeatable and predictable. If you just leave the engine run a little longer (like 20 seconds?) when moving it then it doesn't happen so this is what I do if I'm in that sitaution. It's assumed that moisture, condensation, fuel vapours mess up some sensors on the next day startup.

While I generally try to avoid it, if you're looking to have fuel vapours hanging around, this is one possible way of causing that situation.

 

[rslifkin]

It probably doesn't soak much, but the deposits may absorb the stuff a little better during the cold starts.

I typically run cleaners during a normal tank of DD duty, and make a point at the end of the tank to get it out on the highway for 5 - 10 miles, lock out overdrive to keep it around 3k rpm, and rip on it HARD (accelerate hard, sometimes WOT up to 75 - 80, engine brake to 55, back up to 75, etc as traffic allows).

 

[gathermewool]

I've noticed what you describe as the carwash syndrome on every car I've owned. That's interesting. I wonder if starting the car for 10 seconds a couple of hours after I get home for the night will provide an benefit. Maybe I'll try it for the last few days of DD'ing, before I finish off the second half of the tank on the highway. This way, if it's actually detrimental, what ever gunk the carwash syndrome may produce will only be there for a few days. What do you guys think?

FWIW, I always use either Mobil or Shell, so I'm confident everything is pretty clean. However, I've been seeing unusually high long term fuel trims on occasion while cruising on the highway, so this Redline treatment will be as much as a let's-see-what-happns kinda thing as for preventive maintenance. That's assuming my LTFT isn't due to a leak, which I'll be hunting down on the next dry day.