2000 Buick LeSebre Poor Gas Mileage

Since the weather has turned cold my Lesabre mileage has dropped from 30 to 23 MPG Highway and from 22 to 16 MPG in town. The dealer recently replaced
the Air mass senor, fuel regulator, air filter and cleaned the fuel induction system. They can't find anything else wrong. I was getting 30 highway and 22 in town. They said that it was normal for the mileage to go down in the cold weather that until the engine warmed up to 195 it would get poor mileage. The temperature never gets above 187 and normally is about 180 and that's after one or more hours of continuous driving .
Any suggestions. The temperature averages about 20 degrees lately.
Thanks Bill
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#1 Winter fuel mix, lose around 1-2 MPG #2 Longer winter warm up time, lose big mileage first 5-10 minutes of each drive, if your drives are only 30 minutes long, I would guess another 1-2 MPG loss. #3 Low tire pressur due to cold, even a loss of 3 psi, almost 10%, will cause a drop of up to a few MPG.
180 would be expected at the minimum end if the outside temperature is under 30 degrees F and you were cruising at highway speed. The simple air speed through the radiator when it is that cold is going to lower the engine temperature. Plus the cooling effect of the additional cooling in the heater core. Add the air conditioning compressor load when you have the defroster on as well for additional losses.
I would bet if you cover all the above usual winter losses, that what you are experiencing is probably pretty much normal. Most people experience around a 15% loss in MPG during continued winter temperatures below 30 degrees. Add low tire pressure and you are killing the MPG. Driving through snow around town also reduces MPG as well due to the extra drag load of driving through the slush.
David

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I didn't start taking fuel mileage until engine was warmed up after 30 minutes. I check the tire pressure everyday and is set at recommended level. Mileage was compared was with air-conditioning running in summer. The reason I started checking it was because of the dramatic decrease in MPG when the Air-Mass and fuel regulator went bad. Dealer had mentioned normal Temp when warm as 195. I had a dodge ram before this and it always warmed to normal operating temps throughout the winter. I know each auto is different was wondering if I should partially block the radiator so it would run in the normal temp range?

replaced
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I would then have the dealer test the thermostat to make sure: 1. It is not stuck partially open. 2. It is opening at the correct temperature.
I would also be very suspicious of the condition of the coolant if it has never been replaced through three winters. Not the protection provided, but the all too common start of sludge build up by air entering the system, intake manifold slow and small leaks, improper adding of the wrong coolant or non-distilled water to top off the system.
In any case if they replace the thermostat, make sure to ask that they flush and fill and then bleed the cooling system per GM's instructions.
David

30
30
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What specific bleeding instructions are there for Buick cooling systems? I was thinking of changing the thermostat myself and replacing with new coolant.
Thanks Bill

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Bill wrote:

Bill, I assume that is the 3.8L engine. First, yes, fuel economy will decrease a bit during cold weather, especially if you are driving it short distances. I have the Park Ave. with 3.8L, and once I have driven it ten or fifteen miles in any weather, the coolant temp will be over 195 F, generally either 197, 198, or 199. So, is there any possibility of a cooling system problem on yours, like a stuck thermostat? This is a small item, but check to see if your tires have proper pressure. They tend to get low when the weather suddenly gets cold.
On mine, I'll get about 35-38 mpg on the highway.
---Bob Gross---
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I hope this doesn't sound like a troll post, but I personally find it very difficult to believe that a Park Avenue (or any other mass produced vehicle with the 3.8) could achieve these astoundingly high fuel mileage ratings unless the vehicles was coasting downhill at 45 MPH with a tailwind the entire trip. I certainly do not have the most fuel efficient driving habits, but I've known precious few who have been able to meet or exceed EPA estimates. If my memory serves me correctly, the highest highway EPA ever issued on a Park Avenue was 30 MPG. Assuming your claim of 35-38 MPG on the highway is correct, are you obtaining these numbers from the vehicle's trip computer or driver information center? If so, I'm sure you're aware these often read on the high side and are good for little more than "blinky lights" or to assist with developing fuel efficient driving habits. Every vehicle I've owned with a trip computer or driver information center has consistently read anywhere from 1-5 MPG higher than the actual amount as derived from dividing fuel consumed into miles travelled.
I'm not denying your ability to obtain these figures, but I am curious as to what your secret is to obtaining them assuming they are correct.
Roger
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Roger wrote:

I understand your surprise. First of all, a little history. I had a 1991 Buick Park Avenue 3.8L, and it was an excellent road car. Between San Jose and Bakersfield or Las Vegas, round trip, I could consistently get 36 to 37 mpg. The trick there was that I was driving slow, about 57mph, and trying to get as much draft as possible from the 18-wheelers blowing past me on I-5. Then I got the 2002 Park 3.8L, and it is an excellent road car also. The electronic computer shows it getting 38-39 mpg to Bakersfield, but the actual calculation turns up more like 36-37 mpg. The change there is that the sweet spot is at about 60-61 mph for economy. The EPA rated highway economy is 29, but I cheat by going slower than everybody else. Oh, and I did not say that I stopped at all of the red lights or stop signs. It is not unusual for me to drive with the cruise control engaged continuously for 6-8 hours. If I drive "hard" to Las Vegas, the mileage will be about 30 mpg, even though I never stop the engine. Around town economy is about 20-22 mpg.
---Bob Gross---
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Bob also calculates his MPG using a solar powered Radio Shack calculator that has gradually gotten weaker over the years...........lol
I couldn't resist.
========Harryface ======== 1991 Pontiac Bonneville LE ~_~_~273,437 miles_~_~_
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My guess would be a stuck thermostat, so that the engine is always cooling itself. This will drop your mileage to the mid teens if you drive only around town a few miles.
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zroger73 wrote:

Actual mileage in my case. I get 28mpg on the highway at 70mph. If I drop down to 50mph and do the egg on the accelerator routine on perfectly flat ground, I can keep my speed with the engine in overdrive and ~1400rpm.
I squeezed 40mpg one time doing this. It's all technique. To get maximum efficiency, you need to accelerate about 2mph per second - and let the car shift into overdirive at about 35-40mph. Stomping the gas like we all like to do - not so much.
If the engine never goes above 2500prm, you'll get at least 25mpg.
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Joseph wrote:

Yes, I agree. Drive with one eye on the tachometer, not the speedometer. You can actually cruise down the highway at 1400-1500 rpm. And I agree about increasing speed. I leave my foot off the gas pedal, and increase the speed with clicks on the cruise control, and that is very slow. The 3.8L engine can be very economical, but then there are driving techniques that will help. I think the original poster has something sprung in his cooling system, so his engine is never getting up to normal temperature.
---Bob Gross---
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Hi Bill
I have a 2001 Lesabre with the same engine. Here is my experiance with it so far, after about 1.5 years.
Engine temp: always stabilizes at about 195 once the engine is warmed up, summer or winter. Takes a bit longer in winter time to reach this, about 30 min.
Mileage summer highway ~ 37 mpg CDN gallons = 31 mph US gallons summer city ~ 22 mpg CDN gallona = 18 mph US gallons winter highway ~ 35 mpg CDN gallons = 29 mph US gallons winter city ~ 17 mpg CDN gallons = 14 mpg US gallons.
Living on the Canadian preries I find that after an engine is warmed up, the winter highway mileage does not drop very much once you are crusimg at 60mph. The city mileage is a different story, it starts to drop dramatically as tempetures go down. Presently we are around high of 25F to about low of 0F (-5C to -18C)
Ted M
Bill wrote:

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With all of this talk about gas mileage, it reminds me of the cars of thirty years ago. They were said to get twenty miles per gallon. That is, twelve on the highway and eight in town.
---Bob Gross---
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Thanks All;
I have a new thermostat to install 192/195 rated. My engine temp is stabilized around 180 once warmed up. I did notice if I sit in traffic the engine will warm to 195, but as soon as I start moving again it drops to 180-182. I will install the new thermostat this coming weekend.
Thanks again
Bill

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Bill, I was just driving my car (3.8L) in 50 degree F weather. The coolant temp stabilized at 197 degrees F within three miles.
---Bob Gross---
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