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2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues
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jerrold
Anonymous Poster
jerrodmarten@gmail.com
Aug 6, 2009, 5:23 PM
Post #1 of 3
(7157 views)
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2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues
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As in the title of the post, I have a 2004 3.8L V6 Chevy Impala LS with approximately 110,000 miles on it.
Recently, while my girlfriend and I were taking the car for a drive, the car overheated (luckily as we were pulling into a parking spot at home); I checked the coolant level in the reservoir and there was none in the reservoir. I proceeded to put coolant into the car as instructed in the owner's manual (e.g. opening the bleed valve, adding 50/50 dexcool to the radiator until full, turning the car on to cycle, adding more, etc., filling the reservoir, etc., closing the bleed valve (maybe closing the bleed valve before filing the reservoir, I can't remember, but I know I followed the instructions in the manual.)) Since then, the car hasn't had any issues with overheating and the fluid level seems to be remaining pretty constant (or there hasn't been enough of a loss in the reservoir for me to notice).
However, since I refilled the coolant, I've noticed a severe drop in fuel efficiency. For example, tonight I filled up and compared gallons to miles on my trip meter and realized that since the last fill up I was only getting about 10.5mpg when normally, even in the worst stop and go conditions, I would expect around 18-21mpg.
I'm not sure that the empty coolant system and the fuel efficiency issues are related, however, it seems likely that they are since they sprung up around the same time. I guess it could be coincidence, but again, I think that's unlikely.
I've checked the oil which doesn't seem to show any indication of coolant/oil mixing (e.g. milky white color) and appears otherwise normal.
The climate controls in the car seem to be operating normally (e.g. both the heat and air conditioning operate and seem to normally heat up and cool down, respectively) without appreciably effecting the temperature of the engine.
I haven't check the fuel or air filters as of yet, but they haven't been changed in over a year.
The car seems to run just fine, that is, there don't seem to be any issues behind the wheel like rough starting, rough or loud engine noises while driving, or anything like that; or at least, the car seems to be running alright to me.
I haven't noticed any white smoke coming from the exhaust pipe and when I was running my car after I refilled the coolant, I didn't notice any bubbling over of the coolant reservoir or any bubbles forming in the coolant reservoir. (I think these are symptoms of head gasket issues).
I haven't really checked anything else and don't have any more information about the state that the car's in at this point.
So, my questions are:
What would cause a slow (almost unobservable) coolant leak and a drop in fuel efficiency? Does it seem plausible that these issues are related?
Could these be unrelated issues that popped up at the same time by coincidence? What could be causing either of the problems if they are unrelated?
What other symptoms should I check for to report back about? Or is there any other information that would be necessary to give at least a semi-educated diagnosis of the problem?
That's all I have for now. Thanks.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Aug 7, 2009, 12:43 AM
Post #2 of 3
(7135 views)
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Re: 2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues
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Nice observations jerrold.
Where did the coolant go? A couple things can cause elusive coolant loss, head gasket and water pump are high on the list. Sometimes water pump seal will leak at low pressure and not at high. They will leave an evidence trail of color or a clean spot in lower vent hole between inner and outer bearings of them and may have done this unseen and quit it for now which means you need to look - use a light and dental type mirror for evidence OR while cold if you can put your finger on that vent hole and come back with any coolant at all the pump would need replacement.
 That's not your pump but shows the necessary vent which should not have coolant on it or evidence of dried coolant dyes.
Head gasket: Possible to be intermittent and leave no evidence but it really wouldn't heal on its own. If so it will show itself again in all likelihood. Keep coolant on board at the ready.
Gas Mileage: Forget one tank check. It may have just been the time spent filling up the radiator if engine running and a gallon more that the tank allowed in when you filled would show a major change if you track it - I do. If truly over-fueling the engine it might smell out exhaust and you would have a "check engine" light soon. Check the MPG on a couple fill ups and you might see the next higher than expected - can't be sure too soon with that. Keep in mind - a cruise ship and a moped are both getting ZERO MPG when sitting still
T
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DanD
Veteran
/ Moderator
Aug 7, 2009, 12:53 AM
Post #3 of 3
(7130 views)
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Re: 2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues
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The 3.8 had a bit of an issue with the plastic intake manifold leaking coolant into the intake; after the EGR (exhaust gas recirculation) passageways became distorted due to heat.
If this is the case with your vehicle; it may be such a small leak that it is undetectable at this time (ie: white smoke at the exhaust).
Again if this is the case; yes it could also have a bearing on the fuel consumption. Anti freeze, even in small amounts can contaminate O2 sensors; causing them to send inaccurate information to the computer; which in turn will change fuel mixture.
Anti freeze does not get used up; like what motor oil can. If the system was down there has to be some form of leak.
The cooling system may need to be pressure tested (warm and cold) to find the source of the leak.
As for the O2 sensor; they can be monitored by a scan tool to check their operation. An O2 sensor that is sending out inaccurate information; but has not gone out of its parameters will not set a service code or turn on a check engine light.
Dan.
Canadian "EH"
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