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2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues

3 messages,  Last post on Nov 26, 2009 at 12:40 PM

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#1 of 3 2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues by cliponties Aug 06, 2009 (10:06 pm)
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. Replies to this message: jergold (Aug 23, 2009 7:16 pm) ark5 (Nov 26, 2009 12:40 pm)
#2 of 3 Re: 2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues [cliponties] by jergold Aug 23, 2009 (7:16 pm)
Replying to: cliponties (Aug 06, 2009 10:06 pm) Hello, I have a 2003 Chevy Impala with 112,000 miles on it that is exibiting similar issues. It overheated on me in the fast food drive through a couple of nights ago and the radiator was very low on coolant. These cars are notorious for having coolant leaks around the intake manifold and heater hose outlet from the engine. The Dex/Cool attacks the gasket material causing internal and external coolant leaks and degrades the plastic block fitting in the bypass hose to the heater core. The leaks can easily ruin an engine and while not that difficult to fix, involve a lot of labor and consequently can run into over a grand to repair at a dealer. There was a class action lawsuit against GM where you could recover a portion of the repair bill for the Dexcoolant issue, but it ended last year in October.   I am in the process of isolating where the leak is coming from. I checked the coolant with a block tester and there are no combustion gasses present. The oil looks normal, but I had it changed today because I was worried the high temperature reached when it overheated may have caused viscosity breakdown. I use Mobil 1 synthetic high milage. The engine runs fine as do heater and a/c. The oil change guy said it was leaking from the passenger side, which is where the water pump and heater hoses are.   GM must have known they were going to have problems, because most GM cars with the 3.8 liter engine have a computer program in the engine management system that disables half of the fuel injectors and turns them into reverse air pumps to cool the engine when total coolant loss occurs. Taken from a GM service bulletin: If an overheated engine condition exists and the messages COOLANT OVER TEMPERATURE and REDUCED ENGINE POWER are displayed, along with the Check Engine light, an overheat protection mode which alternates firing groups of cylinders helps prevent engine damage. In this mode, you will notice a loss in power and engine performance. This operating mode allows your vehicle to be driven to a safe place in an emergency; you may drive up to 50 miles (80 km). Notice: After driving in the overheated engine protection operating mode, to avoid engine damage, allow the engine to cool before attempting any repair. The engine oil will be severely degraded. Repair the cause of coolant loss, change the oil and reset the oil life system.   I am taking mine to a "GM Only" repair center this week to see if they can isolate the leak and get an estimate on the repair. I am very dissatisfied with our dealer's service department, as when the catalytic converter went out at 110,000 miles and cost us $2,200 in repairs, they were working right below the intake manifold and could have let us know that this was a potential trouble spot and recommended replacement of the intake gaskets at the same time. The convertor problem was a recall in earlier Impalas but is not covered anymore. No more GM cars for me! The poor milage condition could well be related, do you notice a fuel odor? A leaking intake gasket can play havock with the computerized fuel mixture controls. Replies to this message: ark5 (Nov 26, 2009 12:40 pm)
#3 of 3 Re: 2004 Chevrolet Impala LS 3.8L V6 - Coolant/Gas mileage Issues [jergold] by ark5 Nov 26, 2009 (12:40 pm)
Replying to: jergold (Aug 23, 2009 7:16 pm) jergold   Did you ever find where the leak was coming from? I had a similar problem and the intake gaskets were replaced in Aug. 09. Everything was fine until last Sat. when the car over heated causing me to limp home in low power mode. The dealer could not find anything wrong except for being a little low on coolant. I have a feeling that my issues are not over yet. In addition, the heat will not get hot until the car is driven and then the temp is unbearable. The heater issue and over heating may or may not be related.

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