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E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 08-19-2011, 08:11 PM
jsdugan jsdugan is offline
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95 325i 5 speed 4,000 rpm driving 60 mph in 5th?

I just bought a 1995 325i convertible, and it is quite nice, but I have not driven a BMW before, so I am not sure if this is normal. In 5th gear, I am running about 4,000 rpm going 60 mph. Is this normal? Am I going to get horrible gas mileage on the interstate? Thanks everyone!
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  #2  
Old 08-19-2011, 08:51 PM
DenKare DenKare is offline
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Mein Auto: 1995 325is
i have the same thing yes bad gas... cause i have a modified diff so its super fast accell haha
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  #3  
Old 08-19-2011, 09:09 PM
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You probably have a 3.73 or higher diff ratio. Swapping out to 2.93 or 3.23 will help your milage, but will give slower accel
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  #4  
Old 08-19-2011, 09:17 PM
jsdugan jsdugan is offline
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How would I find out what my differential is?
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  #5  
Old 08-19-2011, 09:34 PM
granlund granlund is online now
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If you're really turning 4000rpm at 60mph in 5th, you most likely have a 4.44 diff from a 318 auto. The original ratio is supposed to be 3.15.
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  #6  
Old 08-19-2011, 10:38 PM
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Theres a tag on the diff. You have to read the numbers on it. I dunno how to decipher off the top of my head, but thats what googles for
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1997 328iS... HR coilovers, Brembo F40 calipers, camber plates, it needs a CUMMINS!!

1990-somethin Chevy K3500... Cummins, cab swap, 5 speed, and lots of motor work. 20 MPG, 40 PSI, 507 ft/lbs torque
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  #7  
Old 08-19-2011, 10:41 PM
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ZeGerman ZeGerman is online now
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You don't have the original differential in your car. At 60mph, it should be between 2.5 to 3k.
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  #8  
Old 08-19-2011, 10:41 PM
jsdugan jsdugan is offline
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I briefly got under there tonight and found the tag, but I couldn't read it. It looked original and rusty in areas like it should be stock. I will check it out more tomorrow. Any advice on cleaning it so I can actually read it?
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  #9  
Old 08-19-2011, 10:45 PM
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Its probably an OEM diff, like out of an auto 318 as mentioned, so it may have seen rust before it was ever on your car. Wire brush should help clean up the rust. Otherwise carefully take it off and try and read it under better light
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1997 328iS... HR coilovers, Brembo F40 calipers, camber plates, it needs a CUMMINS!!

1990-somethin Chevy K3500... Cummins, cab swap, 5 speed, and lots of motor work. 20 MPG, 40 PSI, 507 ft/lbs torque
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  #10  
Old 08-20-2011, 03:18 PM
jsdugan jsdugan is offline
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3:15 . 8991 Ratio

I got under there today, and the differential tag said 315 8991. So, it is the correct differential. I checked out the rpm's again today, and checked my speed on the GPS to make sure it was accurate. At 60 it is turning about 4,000 rpm, and at 70 it is turning about 4,650 rpm. The clutch is not slipping. After inspecting a bunch of stuff today, could any of this be the problem:? The rubber flange or bushing from the transmission to the drive shaft has a rip starting in it (I am sure this isn't the issue), the intake hose, just after it goes into the car, and it looks like it goes down toward the alternator?, is busted and missing a good chunk of it, a cable that runs to some contraption at the front drivers side of the car with a sensor (says VDO 12V) has the plastic cover mostly gone and the metal is exposed, and I pulled the plugs to check them out and I found a little dab of oil where the plug goes, and when I pulled the plugs out they were covered in oil and mostly black, with a little bit of gray. I am also going to post all of this stuff and introduce myself in the proper area for new people. Thanks in advance for the ideas.
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  #11  
Old 08-20-2011, 03:30 PM
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How many RPMs in first gear going 20? None of that would cause high RPMs.
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Please, call me Chadley

1997 328iS... HR coilovers, Brembo F40 calipers, camber plates, it needs a CUMMINS!!

1990-somethin Chevy K3500... Cummins, cab swap, 5 speed, and lots of motor work. 20 MPG, 40 PSI, 507 ft/lbs torque
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  #12  
Old 08-20-2011, 04:21 PM
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I think your tach is screwed up or the tag on the diff is wrong. No way it's turning 4k at 60 with a 3.15. You should be doing 98 mph at 4000rpm in high gear, and about 112 at 4650.

Correction: I thought 5th was an overdrive like 0.93. It isn't. It's 1:1

1995 325i BMW 5 speeds have 4.2; 2.49; 1.66, 1.24 and 1.00 gearing. Guesstimating you have 205-60-15 or equivalent OD tires, your speed at 4000 rpm with a 3.15 differential would be 90 mph. At 4650 you should be going about 105. The diff is either tagged wrong or your tach is way off. You should be turning about 2650 at 60 mph.

Data for this was calculated here:

http://www.car-videos.net/tools/spee...B1=Recalculate

You have to manually plug in the transmission gear ratios and the differential ratio, plus your tire size.
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1995 318is "Bebe"; 1993 325is "Elvira" 1985 635CSi "Katja" 1984 633CSi "Sylvia"
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Last edited by hornhospital; 08-20-2011 at 04:41 PM.
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  #13  
Old 08-20-2011, 05:27 PM
jsdugan jsdugan is offline
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More Info

I went out for another drive, didn't run the air con or anything. When the car was warm, it was idling around 1,600 rpm, and sometimes would be close to 2,000. The car did the rev up and down a little at idle after I got home after I lugged it up the driveway, after it was warm. Tire size is 205/60-15.

1st gear @ 20 - 5,500 rpm
2nd gear @ 20 - 3,200 rpm
3rd gear @ 20 - 2,100 rpm
4th gear @ 20 - 1,400 rpm

4th gear @ 40 - 3,000 rpm
5th gear @ 40 - 2,400 rpm

5th gear @ 50 - 3,200 rpm

Oh, and the 5,500 rpm, pretty much felt like high rpm's. Thanks for sticking with me guys.... This out of all of the stuff I listed on the other thread is the most concerning, because it just doesn't make since!
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  #14  
Old 08-20-2011, 05:41 PM
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I say you have a incorrectly labeled diff. To see if the tach is right you'll need to hit the rev limiter, which is 6500. If you are on the rev limiter (and you'll know because it wont rev up any more) and the tach is at 6500 or so, you have a highly geared diff. You'd have to plug in the known diff ratios into Kens calculator to figure out what diff you really have
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Please, call me Chadley

1997 328iS... HR coilovers, Brembo F40 calipers, camber plates, it needs a CUMMINS!!

1990-somethin Chevy K3500... Cummins, cab swap, 5 speed, and lots of motor work. 20 MPG, 40 PSI, 507 ft/lbs torque
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  #15  
Old 08-20-2011, 05:55 PM
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I'm thinking the tach is incorrect. I doubt you could be idling at 2k rpm without a very serious ICV problem or vacuum leak.

Try the redline test like chad said.
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  #16  
Old 08-20-2011, 05:55 PM
jsdugan jsdugan is offline
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Well, if this is the case, than that kinda sucks. I really don't want to run at high rpm's on the highway all of the time. I guess I may need to look into a swap? Is a really low geared differential desirable to anyone? I guess I will go out and the to blow up my car , and hit the rev limiter soon. Keep the thoughts coming - thanks.
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  #17  
Old 08-20-2011, 05:58 PM
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Hitting the rev limiter isn't going to blow up your car. Just do it while the car is warm, and don't hold it there for more than a few seconds.
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  #18  
Old 08-20-2011, 06:07 PM
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I'm pretty sure the tach will READ way past red line when it finally hits the limiter (but it will still be only ~6500). Are you sure the IC hasn't been swapped, maybe one from a 1.8/1.9liter 4 cylinder? Don't know if that would make a difference or not, just throwin it out there.
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  #19  
Old 08-20-2011, 06:09 PM
jsdugan jsdugan is offline
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So if my tach shows that I idle at 1,600 rpm's, then would it make sense that it is the tach? How could the tach get messed up? Is there a way to check if the tach is functioning properly?
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  #20  
Old 08-20-2011, 06:11 PM
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Idling at 1.6k isn't a sure sign that your tach is bad. Testing the redline, as previously mentioned, would be a sure way to do it, though.
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  #21  
Old 08-20-2011, 06:17 PM
granlund granlund is online now
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If the tach is wrong, then would yo be able to test the lowest rpm then engine can still pull at.

My -92 non-vanos (which is a notoriously poor low-rpm performer) can accelerate gently in 2nd gear from ~500 rpm without starting to buck. If your tach is way off and you try to do the same, your indicated 500rpm would be something like 300 real. This low rpm would cause the engine to nearly stall.
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  #22  
Old 08-20-2011, 06:31 PM
jsdugan jsdugan is offline
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instrument cluster

The mention about the instrument cluster being replaced has me worried a bit. I am going to attach a picture of my IC, see if it looks normal. It was born 11/94. I have not driven other BMW's so I don't know. I did notice that I don't have the mpg gauge.
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  #23  
Old 08-20-2011, 06:47 PM
granlund granlund is online now
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I'm wondering if this is not an older type cluster with the 140mph limit.

You can access some info in the cluster described in this webpage: http://www.bimmerinfo.com/E36_OBC_tricks.htm
Try 'test sequence 02' to see if it reports a 4-cylinder or 6-cylinder engine.
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  #24  
Old 08-20-2011, 06:47 PM
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If you are truly idling at 1600 rpms you should be able to hear that clearly since that's double normal idle. We're not talking a subtle difference here.

If it turns out your tach is correct, one other thought is that your car has had an automatic to 5 speed swap. If that was done and you still have the diff that matches up with the auto tranny your highway rpms are about right.
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  #25  
Old 08-20-2011, 06:51 PM
granlund granlund is online now
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A 325 auto had a 3.91 diff and that's too low a ratio for the 4600rpm at 70mph. I'm thinking of such a diff swap for my 325 manual and it would give ~3900 rpm.
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