awful bloody awful MPG

[Surtr]

Are you running a 50/50 mix of anti-freeze and water? I think having too much water will make it run cooler. But then the thermostat shouldn't open...

[CorvallisBMW]

The resistance of the circuit doesn't change.

Are you sure? I'm thinking that it does, that's how the sensor knows the difference between cold and hot. I've had very similar conditions to what you're describing OP, turns out it was the temp sensor that feeds the ECU. Note, that is a different piece than the temp sender, which operates your cluster temp gauge.

I can't see the pictures here at work, so forgive me, but are we talking about a b25, b27, m10 or m42?

I'd say your fuel economy is directly related to your cold running engine. Fix that and you're MPG will improve, guaranteed.

[llll1l1ll]

Although my car does not have a questionable maintenance history, it does indeed have (estimated) ~260,000 miles on it. It needs lots of tinkering to keep running, and it runs kind of rich. Sometimes. This weekend it didn't. I usually have a 20 minute in-traffic commute to work, both ways, and with added drives to a friend's house here and there, a full tank will last me about 1.5 - 2 weeks - depending on how often I visit my bud's place. I'd say for a twenty-something year old 325is, that's pretty darned good.

Now, my car runs pretty shaky. Probably because there is a cracked-ass vacuum hose somewhere that I need to replace. Super glue isn't working. Duct tape will not, either.

What I'm getting at is a lot like what Mtech 3 said. Basically, don't start dumping tons and tons of money into a car that's already pretty old. There really isn't much payoff to it since nobody but a crazy enthusiast will buy it from you for anything remotely close to what you think it might be worth.

[M-technik-3]

I already seafoamed my car quite a number of times (300000+ miles on a 22year old car is quite the smoke show) so I'm assuming marvel mystery oil works the same as seafoam..correct me if i'm wrong.

The previous owner duct taped the intake hose pretty well :giggle: so I hope there isn't any leaking.

300K Is this an I or an E? regardless this is a high mileage engine with questionable maintenance history so fix the few known issues and try not to throw a lot cash at it because it's honestly getting to the point where it's worn out.

[lolcantturn]

The resistance of the circuit doesn't change.

Oh ok, so as long as its outputting some resistance, it's ok right?

[KenC]

The resistance of the circuit doesn't change.

[lolcantturn]

bump

[lolcantturn]

Yeah '96 is fine.

Yes, ohm out that sensor. Doesn't have to be cold or anything.

but if it's cold it reads out, to my understanding, a different resistance than when it's hot. that difference will show if the temp sensor is reading it too hot, or in my case, too cold. but im just wondering if i measure it when its ice cold.

[KenC]

Yeah '96 is fine.

Yes, ohm out that sensor. Doesn't have to be cold or anything.

[lolcantturn]

Yes. Get a late 90s mustang GT O2 sensor and splice it in. Bosch brand.

Thanks, like 96 will do?

If your car isn't getting to proper temps, you will not be getting proper mileage.

Test your coolant temp sensor. If that gauge isn't close to the halfway mark, fix your shit until it does.

will do. So I let the car sit overnight so it's completely cold, and test the resistance, and it *should* read the resistance stated in the Bentley manual right?

[VasFinest]

OK so if I am reading this right the temp should read in the middle? Mine is almost always just above the blue... Not trying to thread jack, but that concerned me.

[KenC]

If your car isn't getting to proper temps, you will not be getting proper mileage.

Test your coolant temp sensor. If that gauge isn't close to the halfway mark, fix your shit until it does.

Word. Low operating temperature and bad O2 sensor are the two things I would tackle first.

[StereoInstaller1]

If your car isn't getting to proper temps, you will not be getting proper mileage.

Test your coolant temp sensor. If that gauge isn't close to the halfway mark, fix your shit until it does.

[KenC]

Why thank you. I was kinda skeptical to spray a shitload of brake cleaner into my AFM, so I sprayed a little, then sprayed CRC electronics cleaner instead haha.

The O2 sensor is located in the exhaust manifold correct?

Yes. Get a late 90s mustang GT O2 sensor and splice it in. Bosch brand.

[lolcantturn]

Jesus Christ there are idiots on here.

Spraying any sort of solvent into the intake through the AFM will not clean it. You need to clean and inspect the board. And for the love of god don't use carb cleaner or brake cleaner; those are powerful solvents... something you don't want on your circuit board. There are aerosol cleaners specifically for electronics. Get one of those.

Replace that duct taped intake boot.

Check for vacuum leaks.

You're running super rich. Usual culprit for this is a bad O2 sensor... why that wasn't the recommendation in the first reply is beyond me.

If your temp gauge is accurate and you're running that cold, it could also be causing it to run rich.


Running rich for extended amounts of time will foul your catalytic converter so be prepared to replace that as well.

Why thank you. I was kinda skeptical to spray a shitload of brake cleaner into my AFM, so I sprayed a little, then sprayed CRC electronics cleaner instead haha.

The O2 sensor is located in the exhaust manifold correct?