Transmission Fluid Level, Gas Mileage

Smith1000 · #1 06-24-2006, 02:22 PM

I read somwhere that low transmission fluid can reduce your gas mileage. My MPG has been dropping off in my 97 Lesabre, so I am wondering if this could be the reason. I found the transmission fluid was low, so I added some and overfilled it. Will it hurt to run it overfilled for a while? It drips out some and will go down over time. Everything else checks out okay. I used to get about 26 MPH fairly consistently (combined town and highway). Lately, it has dropped to 20-21 MPH, same driving patterns. Thanks.

maxwedge · #2 06-24-2006, 04:05 PM

You have to have the fluid so low it would cause a slip to affect mileage., now an overfill can be the opposite if it is "really" overfilled, the rotating components can be slowed down by hitting the oil and /or cause the fluid to foam up. You must judge how overfilled your trans is. A full scan and fuel pressure check may reveal why your mileage has dropped, assuming the engine is in proper tune.

LeSabre97mint · #3 06-25-2006, 06:58 PM

Hello

I also have a 97 with 110,000+ on it and get 20-21 mpg since I got it with 99,000 on it. I have new O2 sensors and will be replacing them soon. I'll try to report back on any milage inprovement.

Dan

Smith1000 · #4 06-26-2006, 07:16 PM

I replaced my O2 sensor last fall and did some other tune up stuff, plug wires, plugs,etc., but it didn't seem to help. Since then, the MPG has declined, but more so recently. I filled up with gas today, so I should see if my transmission fluid being filled up does any good. I believe I only overfilled it about a quart which probably won't hurt anything. It runs great, no complaints there. It has about 154,000 on it now.

LeSabre97mint · #5 06-27-2006, 12:46 PM

Quote:

Originally Posted by Smith1000

I replaced my O2 sensor last fall and did some other tune up stuff, plug wires, plugs,etc., but it didn't seem to help. Since then, the MPG has declined, but more so recently. I filled up with gas today, so I should see if my transmission fluid being filled up does any good. I believe I only overfilled it about a quart which probably won't hurt anything. It runs great, no complaints there. It has about 154,000 on it now.

Hello

You said you replaced "a" O2 sensor. There are 4 total on this car. I would recomend replacing the two infront of the cats.

I don't think I'll have time for a while to replace my O2's. I will be out of town for a week starting tomorrow. I'll try to post back to this thread when I get them changed.

Regards

Dan

pcmos · #6 06-27-2006, 01:46 PM

Have you checked to make sure you aren't leaking coolant into your engine through the intake manifold? You should check your coolant level, re-fill if low, and if it drops again with no visible external leaks then you've probably got a blown intake. That would result in a fairly significant drop in gas milage and could avoid setting off an SES. As for the transmission over-fill, I made the same mistake after replacing my transmission filter on my 2000. Having it over-filled dropped my gas milage by about 2 or 3 mpg. I had to go purchase a hand pump at pep boys to suck the fluid back out through the filler tube, as I did not want to break the pan seal again. I could also feel a difference in how the transmission behaved with it over-filled, it felt like it was constantly straining, engine temperature was consistently higher also. It would probably be a good idea to simply track down your transmission fluid leak and fix it.

corning_d3 · #7 06-27-2006, 02:25 PM

Overfilling a transmission isn't a good idea..

Smith1000 · #8 06-27-2006, 06:45 PM

I probably should just go ahead and change the transmission fluid and put on a new gasket. The current one leaks. It is one I put on during a previous change. Never can seem to get them sealed right.

I didn't know the '97 Lesabre had 4 O2 sensors. I thought there was just one before the Cat converter (the one to change) and one after. The one I have changed is directly down from the firewall in the exhaust manifold. Where is the other one that is before the cat converter? That could be the problem.

I have done the blown intake fix on it about 3 years ago. I used the kit (Kenco. I think). It worked great and it was a fairly easy job. That is a good suggestion though. The antifreeze level is okay.

It seems like it is getting better mileage on this tank. Could be my imagination though because I keep looking at the gauge. When it was getting fairly good mileage, it would have gone about 210-215 miles when it hit a half tank. Last week it was at about 175-180 when the gauge read exactly a half tank.

pcmos · #9 06-27-2006, 08:51 PM

Are you using the proper torque and tightening order on the pan bolts? If I were you I would probably replace both the pan and gasket at this point, since the pan could be warped if you improperly torqued those bolts previously. It could also be warped if you or anyone else has ever attempted to lift the vehicle with the transmission pan. I followed the instructions from my shop manual on tightening the pan bolts, using a torque wrench of course, with a new gasket, it sealed perfectly the first time. While the pan was off I also carefully cleaned both sealing surfaces until they were spot free using a solvent, which I then carefully cleaned off using soap and water before installing the new gasket. If you need that info from the shop documentation I can give it to you. You may also want to confirm that the leak is in fact the pan gasket and not the fluid line connection dripping down onto the pan. On my 92 I had a leak at one of the hose fittings that trickled down the line and ended up on the pan, dealer replaced the pan twice before I finally crawled under the car myself and found the problem.

corning_d3 · #10 06-27-2006, 11:50 PM

Overtightening is the main reason pans leak, but if you get a good gasket from the dealer, it'll usually be rubber with torque-limiters built in it. At least use rubber if your getting a filter kit.I think 17 ft.-lbs. of torque are all those need. If the pan is warped, it can be fixed. Put it upside down on a flat table and beat around the edge with a rubber hammer until it's flat.

Smith1000 · #11 07-01-2006, 08:14 AM

I'll take a look for that second O2 sensor today and see if the transmission fluid leak is coming from the line or the pan. I think the reason the pans want to leak is because there is usually so much transmission fluid on the bolt threads. It is difficult to get them torqued right. Cleaning the edge with soap for a clean seal might be the way to go. Changing the transmission fluid is always such a mess. I wish they would put a drain bolt on the pan and figure out a better way to attach the pan.

troy1 · #12 07-04-2006, 09:53 AM

you can overfill a 4T60E its actually kind of good for them. when you trans is HOT it can be overfilled about a 1/2" over the top of the full mark. The trans should have a reusable pan gasket if it doesn't that’s why is leaking torque spec is 120 inch lbs

effenfish · #13 07-08-2006, 08:08 PM

I agree with Troy 1. I used the re-usable gasket instead of the one that came with the trans filter. The re-usable one was kind of thick, and had ribs. I used the specified torque on the bolts, alternating from one side of the pan to the other when tightening them, and have had no leaks.

buick24 · #14 08-07-2006, 11:13 AM

so is it better to use the rubber gasket on the transmission than the cork gasket that comes with most kits?

effenfish · #15 08-08-2006, 10:24 PM

buick24, this is from an insert contained with the transmission filter I bought:

"For vehicles using a rigid/molded, reusable pan gasket. If your vehicle contains a reusable pan gasket, DO NOT use the pan gasket found in this kit."

"NOTE: In the event that your reusable pan gasket is damaged, i.e. bent, crushed bolt holes, breaks or cracks, please contact a supplier in your area for a replacment."

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