Correct fuel for 1992 525i M50 Engine

[Blitzkrieg Bob]

I am having a debate with my son over the correct fuel to use for the car. Since the M50 engine has 10.0 to 1 compression ratio shouldn't premium gas be used as opposed to regular. Premium always runs better but he wants to pinch some pennies because of rising gas prices.

I use the mid grade in my M50tu and the S38, I think it's 89 octane.

[Al Gray]

I am having a debate with my son over the correct fuel to use for the car. Since the M50 engine has 10.0 to 1 compression ratio shouldn't premium gas be used as opposed to regular. Premium always runs better but he wants to pinch some pennies because of rising gas prices.

[duby55]

Premium unleaded[90 AKI or 95 Ron] for my 91 525i with the M50. I've ran both regular and premium fuels in my car and it does run better with premium fuel. I fear higher maintenance issues from running regular fuel, so I prefer to spend more for better fuel that could save me from having idle problems, shorter spark plug life ect..

[Blitzkrieg Bob]

Owners manual and the inside of the fuel door says premium for the m50 525i. I don't see why you would go against manufacturer's recommendations.


I remember mine as going by the octane.

87 = regular

89 = ?

92 = super

I'll have to check again

[Mendozart]

I use to run mid-grade (89) in my 92' m50 with no problems. But, with the EAT chip installed, I have to run premium.

[Torque]

Owners manual and the inside of the fuel door says premium for the m50 525i. I don't see why you would go against manufacturer's recommendations.

[Al Gray]

I use to run mid-grade (89) in my 92' m50 with no problems. But, with the EAT chip installed, I have to run premium.


How do you like that EAT chip? Have you noticed a big improvement in performance? If so is it in the lower RPM range. The 525i automatic can be a bit of a slug from the standstill. Also, have you noticed any improvement in fuel economy with the EAT Chip? We are thinking of putting one in as the next improvement to the car.

Al Gray

[Dave M]

Owners manual and the inside of the fuel door says premium for the m50 525i. I don't see why you would go against manufacturer's recommendations.

Always regular 87 octane ;)

Never a ping, don't even know what one sounds/feels like. Always 30+ mpg on long HW hauls. Why spend more. Oh, in Canada, if that makes any difference.

Dave M

[Russell]

I have had the EAT chip in my 95 for at least two years. Seems much better low speed performance. Cars seems more eager in lower rpms. However, I do notice a stronger acceleration at agout 3,500 rpm on up. No real change in gas mileage. Still get 22-24 mpg average commute on mixed and highway driving. Can get over 30 mpg at 65 mph.

With chip requires at least 91 octane (was 89 factory). I typically use Chevron 93 with Lucas UCL added at a ratio of 2 oz per 10 gallons.

[Dr. evil]

i use 90 oct. when i use anything less i notice that i have to push the pedal harder for accel.

[Morgenster]

I use 98 octane (European denomination) or 100+ octane when on LPG.
So what's that in US octane ratings?

[Sam-Son]

the minimum for the M50 is 89. 91 with any kind of chip

[philbyil]

as I installed a JC chip some years back ;)



I am having a debate with my son over the correct fuel to use for the car. Since the M50 engine has 10.0 to 1 compression ratio shouldn't premium gas be used as opposed to regular. Premium always runs better but he wants to pinch some pennies because of rising gas prices.

[94_e34_525i]

The m50 has knock sensors so it really doesnt matter what fuel you put in it....unless you have a chip (which changes the timing) so you need 91...but 87 89 91 93 all work in the m50 (stock chip) it all depends on what performance you want...