PAUL T Posted March 11, 2010 Report Share Posted March 11, 2010 While fixing my starter I had the intake out. When I went to loosen the bolts I noticed that on 6 of the 8 bolts I could turn out with my fingers. When I went to put the intake back on I decided to clean the surface on the heads. There was some carbon and a little greasy residue on them. I got them all shiny, then wiped the mating surface off on the intake and bolted it back in. I then snugged the bolts up and put everything back together. Last night while driving back from church I noticed the average MPG starting to get higher after being reset when the battery had been unhooked when I repaired the starter. The drive was about a 40 mile round trip on country roads and a few miles through town. Lately the average MPG's had been hovering around 19 to 21 MPG but, coming home it went to 24 MPG's. That is the highest MPG's I have ever had even when driving on the highway. Could cleaning the surfaces between the intake and heads have boosted the gas mileage by 2 to 3 MPG's? I will monitor it over the next week and report back. Has the gas companies gone back to summer formula yet? Link to comment Share on other sites More sharing options...
Texas Jim Posted March 11, 2010 Report Share Posted March 11, 2010 While fixing my starter I had the intake out. When I went to loosen the bolts I noticed that on 6 of the 8 bolts I could turn out with my fingers. When I went to put the intake back on I decided to clean the surface on the heads. There was some carbon and a little greasy residue on them. I got them all shiny, then wiped the mating surface off on the intake and bolted it back in. I then snugged the bolts up and put everything back together. Last night while driving back from church I noticed the average MPG starting to get higher after being reset when the battery had been unhooked when I repaired the starter. The drive was about a 40 mile round trip on country roads and a few miles through town. Lately the average MPG's had been hovering around 19 to 21 MPG but, coming home it went to 24 MPG's. That is the highest MPG's I have ever had even when driving on the highway. Could cleaning the surfaces between the intake and heads have boosted the gas mileage by 2 to 3 MPG's? I will monitor it over the next week and report back. Has the gas companies gone back to summer formula yet? You state that 6 of the 8 bolts...you could turn out with your fingers.... My guess is that the intake was loose enough to suck in enough air to throw the mixture off. Obviously not loose enough to set codes...but enough to mess up the mixture. Now that it is all tight... it is running like it is supposed to. Just mu old shadetree mechanic idea. Link to comment Share on other sites More sharing options...
BodybyFisher Posted March 11, 2010 Report Share Posted March 11, 2010 I read this earlier and thought the same as Jim, odd that if it was sucking air, it would not set a lean code, but it must have been under the threshold. I forget, is this on the 94? 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...
mike27513 Posted March 12, 2010 Report Share Posted March 12, 2010 Good Question on the Summer Bland- Refineries normally switch over in March to summer mix so I don't know if they are at the pumps yet. And of course due to this gas prices historically go up [ due to "driving season" ?]. Gas will probably range between $3-4 gallon this summer depending on the upward top of oil prices. And assuming Israel and Iran don't go at each other. Best tune it up to get the best mileage possible. Inflate those tires, etc. My 03 DHS gets 28-30 MPG on flat "down east" coastal plain highways here in NC at 55 mph. Less when in the NC mountains of course. Link to comment Share on other sites More sharing options...
PAUL T Posted March 12, 2010 Author Report Share Posted March 12, 2010 I forget, is this on the 94? This is on the 98 Deville. The 94 became a victim to pulled headblolts. I have taken it for a few short trips to town & back (about 20 miles round trip) and it is still hovering around 23 MPG which is still better than 19-21 before. I have a 100 mile round trip Saturday so I will see what happens. I also cleared all codes out yesterday, so I will see if anything comes back. My mother-in-law just bought a low mileage 2004 Deville and it is loaded with electronics and even has the air-conditioned seats. They have been wanting me to look at it and drive it but I am afraid I will get car fever. My 98 pays off in about 6 months and I am trying hard not to sink that payment into a newer one. Link to comment Share on other sites More sharing options...
KHE Posted March 13, 2010 Report Share Posted March 13, 2010 I forget, is this on the 94? My mother-in-law just bought a low mileage 2004 Deville and it is loaded with electronics and even has the air-conditioned seats. They have been wanting me to look at it and drive it but I am afraid I will get car fever. My 98 pays off in about 6 months and I am trying hard not to sink that payment into a newer one. You will like the '04 Deville - I bought my '05 last October and am very happy with the car. My Fleetwood Brougham is still my favorite car but the Deville is a very close second. Kevin '93 Fleetwood Brougham '05 Deville '04 Deville 2013 Silverado Z71 Link to comment Share on other sites More sharing options...
PAUL T Posted March 17, 2010 Author Report Share Posted March 17, 2010 Update: After about a week of combination town and city driving the avg MPG is still holding at 21. That is still 1-2MPG better than before. Link to comment Share on other sites More sharing options...
Texas Jim Posted March 17, 2010 Report Share Posted March 17, 2010 Update: After about a week of combination town and city driving the avg MPG is still holding at 21. That is still 1-2MPG better than before. Very good. Always glad to hear good news. :D Link to comment Share on other sites More sharing options...
PAUL T Posted March 19, 2010 Author Report Share Posted March 19, 2010 I gave her some more much needed TLC today. I took my good tires of of the 94 Concours and put them on the 97 one was flat so I am going to get that fixed tomorrow. Also recharged the air-conditioner and it is cold now. Added new wipers then checked the codes and there was none. Life is good again for awhile. Link to comment Share on other sites More sharing options...
Texas Jim Posted March 19, 2010 Report Share Posted March 19, 2010 Everything is always better with NO CODES. :D Link to comment Share on other sites More sharing options...
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