1985 bmw 535i. Will run for an hour then it turn off

Question

it will start and I will drive it for about an hour then it turn off it will take an hour to start again what it could be? Thank you

Answer 1

I had this same issue on my BMW a couple years ago.  I had a 85' 735i that would run for a hour sometimes a little less then just die on me.  After a brief cool down period it would start right up normally.  My problem ended up being the Oxygen Sensor or O2 sensor.  This sensor measures the mix of air to fuel ratio and will run a car rich when going out and kill your car.  It should be replaced on every major tune up as well to help give you MUCH better gas mileage.  That is where I would start to begin with if you have never replaced it or know when it was replaced.  I would then move on with this list of trouble shooting tips.

http://www.autozone.com/servlet/UiBroker

The sensor is a bit pricy and can be bought at your local auto zone.  however but really where I would start.  Good luck!

Answer 2

Repairs based on guesswork without benefit of diagnosing the car itself

is usually costly, time consuming and very frustrating.

Sometimes, it turns out the guess is right, but more often than not, it is wrong for there are so many things that can cause the same symptoms.

Bring your car for diagnosis to a competent BMW mechanic.

Would you treat your son or daughter or mother's ailment based on somebody's "experience" and guesswork?

Answer 3

I saw your question earlier this afternoon and was thinking about it for awhile.  Called a few other real BMW techs.  One said sometimes the O2 sensor gets a metal flake on it and taking it out and cleaning it out with compressed air fixes them right up.  He had a story how he figured this out.  Its an od ball thing and is very rare to happen (I see another guy suggest the O2 sensor) But I have been driving REAL bmws like yours for years and have never ever ever had a REAL bmw let me down.  When the newer junk BMWs came out I bought a 1988 and 1989 535 and 735 and the bolth let me down a few times. I will not DOWNgrade to a NEWER BMW ever again...