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Discussion Starter · #1 ·
Sorry if it's been discussed already.
All I find is hydraulic vs mechanical tensioner.

Well apparently mechanical belt tensioner can be mechanical or automatic. Maybe I'm confusing some terminology.

I guess I needed automatic, but bought mechanical. Didn't even know there were 2 kinds!

Well I didn't even realize they were different. Installed it and it made crazy noise and overheated all pulley within seconds! Removed the new tensioner, installed old one and all is well!

If there a way to adjust the mechanical tensioner or anyone ran into this problem before? Hard to tell the difference between the 2!







 

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‘89 325i, ‘98 528i, ‘99 528i, ‘03 325i
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Did you enter your last 7 VIN digits on realOEM? The terminology is “mechanical vs. hydraulic” and they change at different build dates.

In my case, the A/C tensioner is mechanical (spring) and the main serpentine is hydraulic.
 

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When properly installed, they're both automatic.

Get the proper one for your MY.
 

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The mechanical and 'hydraulic' tensioners are interchangeable. Both are automatic and dynamic. (The alternative is a spring that only sets the initial tension, with the pulley clamped into that fixed position. This is frequently used on timing belts where additional tension is not desired.)

Note that the AC tensioner and main accessory belt tensioner are similar but not compatible. That's not likely your problem, but it's a potential problem.

Also note that there are several variations

The original 'mechanical' tensioner was apparently a source of customer complaints. The plating on the internal torsion spring would corrode and wear, causing loud squeaks.

The 'hydraulic' tensioner is actually a coil spring operating in an oil-filled cylinder to slow the response and reduce the tendency for the system to oscillate. The reduced movement, oil-covered spring and greased needle bearings avoid most of the noise from the system. But now there are multiple points that can wear and fail, including the rubber boot on the spring.
 

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Discussion Starter · #5 ·
It was proper based on rock auto.
I know about the hydraulic one, but didn't know about different mechanical ones.
On rock auto listing one mechanical is called auto, and the other mechanical is called mechanical.

They're clearly different, even though it's apparently the same year for the vehicle. Maybe 2 different mechanical versions based on the month of the build. I think they might've changed the design in 03/1998 and my car is 05/1998.

That's why I don't shop on rock auto anymore, I buy from fcp euro.
 

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Remove the pulley from the old and replace it with the pulley from the new. Use the old bolt with medium thread lock if necessary, that way you can reuse the protection cap/lid/dust cover from the old. This way you didn't totally wasted your money with the purchase.
Usually the pulley goes bad and not the tensioner.
Both Ac Delco and Gates are very good brands.

Sent from my SM-G986B using Tapatalk
 

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Don't assume that Rock Auto has the correct parts listing.

I know from experience that Rock Auto will list incorrect parts, and refuse to accept responsibility or even fix the listing.
I'll occasionally buy parts from there, but only after cross-checking the part number and only if there is a big enough discount to make it worth the potential pain.

Older engines didn't come with dust covers over the bearings. Some aftermarket replacements aren't the correct shape for the dust covers to fit.

Certain older models didn't have the deflection pulley on the alternator upper bolt, and some specified a 5mm shorter belt to compensate. My 1999 Z3, with its light electrical load, doesn't have that deflection pulley. Some tensioners will not extend far enough to maintain pressure when using the 'standard' length belt.
 

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Discussion Starter · #8 ·
Yeah I think I'll use Taz advice and just replace the pulley.
I emailed rock auto, they don't seem to care too much. I told them it's ok if they don't refund me but I told them to correct the listing on their website to prevent others from making a mistake.
It's really frustrating installing the wrong part.
This is how I ended up breaking the overflow radiator nozzle, taking thing apart and putting them together too many times.
This tensioner was just too tight. After a few seconds of the car running, the alternator pulley got so hot I touched it for a second by accident and got a burn on my arm.
It's even more frustrating when you change a few things at the same time and it doesn't work right, so you're left wondering if some part is defective, if you screwed up installation...and what part exactly is causing the problem.
The sucky thing is that both tensioners really do look alike.
Well lesson learned. I think with rock auto it's a good idea to buy parts that have a "heart" next to them.

I dont know if they just sent me a wrong item.
According to the part numbers, some come up as hydraulic, some as mechanical, but they should all fit, while the one I got does not work properly

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