dougbrainerd Posted March 30, 2008 Report Share Posted March 30, 2008 Hello All. In my owners manual it is stated that the 2000 Deville, standard engine will run fine on regular 87 fuel BUT for optimum performance use high octane. I used to buy premium but when fuel prices went nuts 2 years ago I switched to 87 with no noticable difference. Last week when I drove it to Myrtle Beach (golf orgy) it was getting 24 MPG on 87 but did 28 on premium. Simple math shows that running premium on the highway is the best value. Another interesting phenom was that the car did better on fuel at 75 degrees than at 30 degrees. Maybe most people already knew these gas facts but I didnt. Golfnut out Link to comment Share on other sites More sharing options...
JohnnyG Posted March 31, 2008 Report Share Posted March 31, 2008 Another interesting phenom was that the car did better on fuel at 75 degrees than at 30 degrees. What are these temperatures? Are these ambient (outside) air temps or fuel temps? When you say "better" I assume there was a small mpg increase at higher ambient temps. This could be caused by shorter warmup, greases and lubes in the drive axles being warmer and less stiff, or just the type of motor oil you are using. Not too surprising when you think about it. I would agree that a 4 mpg increase with higher octane fuel is a little surprising, but once again, other factors might be at work here. Like the possible absence of ethanol in the premium fuel, only because you bought it at a different station. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
Ed Hall Posted March 31, 2008 Report Share Posted March 31, 2008 A 4 mpg increase with higher octane fuel is also a little surprising to me. My 93 calls for high octane fuel but I usually get 1 mpg better with the low octane stuff but loose a little power. Low octane fuel has more BTU's (more energy per gallon) as well. Link to comment Share on other sites More sharing options...
Texas Jim Posted March 31, 2008 Report Share Posted March 31, 2008 If there are more BTU's in low octane fuel, why does it have less power? I thought an internal combustion engine was just a heat pump... therefore more BTU's should equal more power. Not trying to be argumentive... just asking for my own education. Link to comment Share on other sites More sharing options...
dougbrainerd Posted March 31, 2008 Author Report Share Posted March 31, 2008 All fuel was bought at BP stations. There are alot of possible factors but mpg averages were noted over long (400 mile) highway driving at 70-80 mph. The temp differences I was noting was air temp. Another possible factor could be the higher altitude of the mountainous driving vs. the sea level driving. Not very scientific but this is what my trip computer was telling me Golfnut out Link to comment Share on other sites More sharing options...
Texas Jim Posted March 31, 2008 Report Share Posted March 31, 2008 I get about a 2 MPG DECREASE in mileage and a significant loss in power when running regular. When you punch it to pass... you can tell. I have checked it several times on highway driving when on long trips. It is consistent on MY car. Of course other cars may and WILL be different. Just reporting on mine. That means that at 20 mpg on regular and 22 on premium...which is what it gets on the highway, on each 20 gallons, I can go 40 miles farther down the road on premium. It would take me an extra 2 gallons of regular to go the same distance as premium. Two gallons of regular at $3.25 a gallon is $6.50. The difference in 20 gallons at $3.25 for regular and $3.50 for premium is $5.00. It is just as cheap for "ME" or maybe a tiny bit cheaper to use premium instead of regular. Plus the car runs SO MUCH better. Or at least I THINK it does. Link to comment Share on other sites More sharing options...
Ed Hall Posted March 31, 2008 Report Share Posted March 31, 2008 If there are more BTU's in low octane fuel, why does it have less power? I thought an internal combustion engine was just a heat pump... therefore more BTU's should equal more power. Not trying to be argumentive... just asking for my own education. Octane rating is a measure of burn time, not BTU yield. Faster burning gasoline will cause "knocking" in an engine that isn't designed to handle it. If your car calls for 87 octane, run high quality 87 octane. Running 91 or 93 octane is wasted money. A higher octane number means slower burn time. Not hotter, not richer, just slower. Also, higher octane gasoline usually has slightly less BTU's because there are additives with low BTU's that are used to bring up the octane. However, if your car was designed to burn on higher octane fuel, it may run more efficiently on this type of fuel mainly due to more spark advance. Link to comment Share on other sites More sharing options...
dougbrainerd Posted March 31, 2008 Author Report Share Posted March 31, 2008 The owners manual is confusing. It says 87 is fine BUT for optimum performance use premium. Link to comment Share on other sites More sharing options...
Ranger Posted April 1, 2008 Report Share Posted April 1, 2008 The owners manual is confusing. It says 87 is fine BUT for optimum performance use premium. That's because of the knock sensor. If it detects a spark knock on heavy throttle, it will retard the timing appropriately. Thus a slight degradation in performance (you might not even notice it). If you're gonna race it, use premium. If not, regular is just fine. Link to comment Share on other sites More sharing options...
BodybyFisher Posted April 1, 2008 Report Share Posted April 1, 2008 I have found that I can use 87 in the winter but in the summer 87 will knock too much and the PCM will retard the timing and you will feel a performance hit. I run 89 all year long now Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
dougbrainerd Posted April 2, 2008 Author Report Share Posted April 2, 2008 Golfers Joke - The guy I played with today played so bad that he had to regrip his ball retriever Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.