Towing with premium fuel

[Webwader]

Since I started towing with the RL, I have used regular gas (87 octane) and at 13-16 mpg pulling either a 3,500 folding trailer or a 3,250 lb. boat, felt that I was getting acceptable fuel mileage for the load (8,300+ lb GCVW) and although Honda recommends premium fuel when pulling “heavy loads”, I didn’t know if it would help as I was 1,500 lb under the towing limit. But after getting a Scangauge I noticed that when going uphill under load that the ignition timing sometimes dropped as low as 2 degrees BTDC. When not towing the timing never dropped below double digits. I interpreted this as the anti-knock sensors at work and that maybe using premium fuel may keep the timing more advanced and thus improve power and MPG. Since I was leaving on a fishing trip that my fishing partner and I do twice a year and that I had MPG records for, it would be a good time to make a comparison test. I always leave with a full tank and we always stop at the same station going both ways, so the variables are minimized. The one big variable would be the wind in the Columbia Gorge which can vary from nothing to very strong. The route has plenty of mountains and hills where if premium is going to help, this would be the place. . The elevation change one way goes from almost sea level to +4000 ft. and ends at about 2000 ft. with many ups and downs in between.
The average for the two times I have made the trip with the RL was 13.3 MPG with the best fill up being 14.26 MPG and the worst 12.46 MPG (coming home with a strong head wind in the Gorge). When I filled up before I left the RL only took about 14 gallons so I actually started with a blend of regular and premium fuel (91 octane). The average MPG for the trip turned out to be 16.3 with the best fill up being 16.58 MPG and the worst 15.89 MPG.
The wind in the Gorge was non-existent coming home when it would have been a head wind so the mileage spread is a little skewed in favor of premium fuel but the difference is great enough that I am convinced of the value of using premium when towing. Also, the ignition timing when towing almost never dropped out of double digits and then only briefly to 8 or 9 degrees BTDC.
Along the route there is a place called Cabbage Hill, which is a 6+ mile 6% grade on I84 in eastern Oregon. I set the cruise at 55 mph and the RL makes the climb at 34-3500 RPM in third gear. I found it very interesting that during the entire climb the Throttle Position Sensor never exceeded 50%. Who says the Ridge doesn’t have enough power if it can pull that kind of grade at half throttle? On the way up I reset the Current MPG setting on the Scangauge and got 8.3 MPG on the way up. On the way back I reset it a the top and got 70 MPG on the way down. You can coast all the way down at 60-65 MPH and I only had to use the brakes once on a curve.

[blconnection]

I have had a CRX for years along with a buddy. We have had a long debate on that motor about premium vs regular vs MPG due to ping detection and timing advance. First real numbers that I have seen, thanks!

How are you reading timing advance numbers?

[Webwader]

How are you reading timing advance numbers?

I have a Scangauge II. When using the guage function, which can show four parameters, I usually have it set for TPS (Throttle Posistion Sensor), IGN (Ignition Timing), LOD (Percentage of load for the current throttle position), and MPG (MPG in two second increments). It can read any parameter put out by the OBDII port.

[blconnection]

Understand, Thanks, Have been considering buying a OBD reader myself.

[gonzo's rt]

Makes sense. 87 octane will do good, but towing heavy loads, in order to keep the knock sensor from lowering your ignition timing, a higer octane fuel will definitely help. I guess that is why the recommend it.
Honda makes a great product, in the last 20-years and may Honda cars, I have always used 87-octane and never heard a knock coming from the engine. I wish I could say the same thing about other car makes I have owned...

[Pug]

I was thinking of switching temporarily to 89 octane gas during the winter months to attempt to offset the power/performance liabilities of the "winter gas blend" we have here in PA.

Do you think this is a viable "fix" even though I don't tow?

I, too, have the SGII, and use it regularly. I've noticed with the last fill-up, that I'm getting 2-3mpg less with the 87 octane I'm using.
I fill-up at the same pump each time and believe my SGII has been as accurate as it can be. (It has reported the amount of gas used to be within only a tenth of a gallon that the pump says, for the last 5 fill-ups).

Even though I might not get better mpg, do you think there will be a power/performance increase if I do go to 89 octane? And will this cause "changes" in the sensors that may be deleterious to the RL's overall "health"?

Thanks,
Pug

[Webwader]

Pug, the only way to know if it will make a difference is to try it. Unlike my situation where the anti-knock sensors were coming into play due to the load, your loss of fuel mileage is caused by a lower heat content in the gas. I don't know if 89 octane will help or not.
You may gain a little performance but maybe not enough to really notice. There will be no adverse affect in anything. The only sensor that notices the difference is the anti-knock sensor and that lets the electronic ignition timing know how far it can advance for any given situation. I am currently running on a tank of premium with very little towing miles on it. If I notice any increase in fuel mileage from regular I will let you know.

[Rigeline19]

Webwader when you were going down the long grade, did you use D3?

[Brent]

Thanks Webwader. Gott a get a Scanguage gut yhis helps for the inbetween time

[Webwader]

Webwader when you were going down the long grade, did you use D3?

No, I didn't need to. I just coasted. It's a consistent drop, so I never exceeded 65 mph. I only had to use the brakes once for a slower corner and then kicked Grade Logic off by accelerating a little. On a long decent with varying degrees of grade, I like to use cruise control. It then uses Grade Logic to select the right gear (down to 3rd) to keep the RL to the set speed. Of course this doesn't work if the grade is too steep and you do have to get on the brakes, which disengages cruise. Then its D3 and brakes, or a lower gear if necessary.