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Do we have hydraulic or mechanical serpentine polyribbed drive belt tensioners?

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140K views 93 replies 28 participants last post by  bluebee  
#1 · (Edited)
How do I know if I have a 2002 6-cylinder engine with hydraulic belt tensioners or a 6-cylinder engine with spring-loaded belt tensioners?

On page 020-17, the Bentley manual shows an incomprehensibly grainy picture of both polyribbed serpentine drive belt systems - which is bad enough; but it's worse because you can't easily "see" the various pulleys and tensioners inside the actual engine compartment.

Since the Bentley does not say WHICH cars have hydraulic vs spring-loaded belt tensioners - and since I don't know what to look for (or even if it's possibly to "see" them from above - I ask ...

How do we know whether we have hydraulic or mechanical drive belt tensioners on our BMW E39 engines?

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#3 ·
The hydraulic tensioner superseeds the mechanical ones. I don't think you can find a mechanical one for sale anymore.
The new hydraulic tensioner p/n you will have to order is 11287838797 (this is for a 2002 525). I am not sure if car ever had a mechanical tensioner, but if it had one, the new design will not ressemble with the old one (mechanical vs hydraulic)
 
E
#7 ·
I think you can (or could a few months ago) still get the mechanical ones from NAPA.

Pics here: http://www.bimmerfest.com/forums/showthread.php?t=443038&highlight=

I have around 3000 miles on my replacement so far with no complaints. I believe you can convert from mechanical to hydraulic, but IIRC the cost for the kit was much more.
 
#11 ·
Doru is correct.
The hydraulic tensioner supercedes the mechanical tensioner.
There were too many failures with the mechanical tensioners, so BMW went back to the hydraulic tensioners.
And, yes, if you have a mechanical tensioner, you can install the hydraulic tensioner.
I had my mechanical tensioner replaced with another mechanical one.
Two months later, I had to replace it again, but this time with a hydraulic tensioner.
 
#12 · (Edited)
Jason5driver said:
if you have a mechanical tensioner, you can install the hydraulic tensioner
Click to expand...
Well, if they're interchangeable, they must look similar, at least in outline where bolts attach. That would make visual identification problematic.

Looking at realoem, it's still very confusing because BOTH mechanical and hydraulic belt tensioners are shown for the same serial number!

How confusing is that! Here's a screenshot of realoem's $70 (nominal) hydraulic tensioners and the mechanical tensioner. If they're interchangeable, they certainly look different! I guess that's why folks say to just look.

At least now I know a bit more of what to look for, but, as stated, it's pretty packed in there; but with these diagrams, I have yet another nugget of information to look for.

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#14 ·
#15 ·
Realoem didn't provide any clear idea whether I have hydraulic or mechanical serpentine drive belt tensioners; but the consensus is much closer to hydraulic than mechanical.

Now that I have a much clearer picture of the different look of the hydraulic versus the mechanical, I might now be able to look inside the engine to see if I can tuck my camera down there amongst the belts to confirm which is what I have.

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R
#19 ·
Just replaced entire cooling system on my '03 530 and found I had the mechanical tensioners. Once the shroud, fan/clutch and radiator are removed it's possible to see what you have. I ordered both types from Pelican with the understanding I could return the unused new part, which I did without problem. The fact that Pelican could not tell me which type I had leads me to believe both types were used on M54 engines in '03 and maybe other years too.
 
#20 ·
The consensus seems to be that it's a crap shoot whether we have hydraulic or mechanical tensioners, which makes it harder to order parts ahead of time.

We just have to look and see. Here's what the two parts look like side by side.

Based on information in this thread, it might be that one system has one fewer idler pulley than the other system (needs to be confirmed) so a good test would be the number of "round things" (not all of which are pulleys).

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#21 ·
mechanical tensioner

Pretty sure all is the same except the tensioners themselves, both types will have an idler pulley, as mentioned you need a "kit" to change from mechanical to hydraulic, I have mechanical on my 02 530i, will be changing them with mechanical when I do the cooling, you can get them from oembimmerparts (site sponsor).
 
#22 ·
Blue, I had the same issue before doing my major overhaul as well. RealOem will show both because they used both, and their is no VIN# or year to go by in determining what they put in your car that day.

The only true way to be sure is to look as indicated by CN90, if you can get the car on a lift and remove the engine guard, it makes it much easier to see. Both the hydraulic and mechanical bolt on the same way

I had mechanical and ordered new mechanical tensioners. for those who are unsure, you can order the complete upgrade kit to Hydraulic as mentioned, although it will cost a bit more.
 
I
#24 · (Edited)
its really not that hard to determine. you don't even have to jack up/lift the front end, you just remove the engine guard and peer up at the a/c belt. you'll see a hydraulic tensioner or you won't.

pardon the cruddy pictures, I was doing it blind as I didn't want to open the garage door (its raining)
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#25 ·
The only way to know what you have for sure is to look on the e39s. I have 2 1998 528i cars in the family, built a month apart from each other. One has mechanical AC tensioner, the other hydraulic. Both have a mechanical tensioner for the main belt. One has over 170k miles and is smooth and quiet, the other was changed at 120k when it got squeaky.

I've had excellent luck with both types of tensioners. I actually am fond of the simplicity of the mechanical tensioner myself.
 
#26 ·
Mark@EACTuning said:
One has mechanical AC tensioner, the other hydraulic. Both have a mechanical tensioner for the main belt.
Click to expand...
OMG!

Not only do we have the prospect of mechanical or hydraulic ... but we can have both on the same E39!

Thanks for that information (I wish I didn't know it ... but now I realize I need to look at BOTH to figure out what I have).

:)
 
#27 ·
I am really not so sure what all this fuss is about.
They are both interchangeable. It really does not matter which one you have. If you want to switch from mechanical to hydraulic or vice-versa, you can do it with no ill effects.
One is more expensive than the other one. Also, a few people experienced better service with the hydraulic type. Other experienced better service with the mechanical one. BMW "recommends" the hydraulic one. Pick one and be done with it.
 
I
#28 ·
the 'fuss' is over ordering the parts. you have to figure which you have before you order, or do like Rjim and buy both and return the unused one, but thats $10 or so in return shipping...

what I find silly is the BMW dealer can't tell you what was put on via your VIN, thats like a hospital (that you visit often) not having your blood type on file, especially here and now in the computer age.
 
#29 ·
Right, but again, if you had an hydraulic tensioner and you ordered a mechanical, you can replace it no problems. And vice-versa. You might be baffled when you take off the tensioner and it does not look like the original one you had, but it fits and works.
Probably that;s why BMW did not payed such attention to this detail, and maybe that's why you have same model/year cars with different setups, and not recognizable by VIN.
It's not such a dramatic part that will fubar your system if switch them (like for instance you pick a 90A instead of a 120A or 140A alternator). It's almost like changing tires - Michelin vs Dunlop or similar.
 
#30 · (Edited)
As doru is saying, it does not matter which one you get as they both bolt on the same way. So if you had mechanical and buy hydraulic, or vice versa....it will still work. It is just a matter of what you want to believe. some like the simplicity of mechanical and go with them, and some, including BMW recommend the hydraulic. mechanical are also a bit cheaper than the hydraulic if price is a concern.

just choose one and go with it.....
 
J
#31 ·
You can just replace the hydraulic tensioner itself and not the entire assembly. (save some $$)

Here is my old one that was original to the car at about 175,xxx miles:

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The rubber boot holding the oil in was intact .. the bushing on the large end .. not so much. Spring compression force was similar to the new one that replaced it.
 
#32 ·
I dunno about the "just pick one" approach either. I had recently taken my moms hydraulic AC tensioner off and attempted to put a mechanical AC tensioner in it's place. I wanted to change it since her tensioner was broken and I had a spare mechanical tensioner. Was not happening. It would not bolt up. You can retrofit a hydraulic onto a mechanical car with the right parts, but not the other way around in my trials and errors. The bracket that holds the AC compressor and tensioner to the car is different.

I ended up having to order the base for the hydraulic AC tensioner to fix her AC, which retails over 100 bucks. Hopefully I can salvage the rest of her old hydraulic parts onto the new base when it arrives and get her AC working. It's getting warm during the days! The base I had to order looks identical to this: http://www.bimmerfest.com/forums/showpost.php?p=5235584&postcount=14
 
#33 ·
Thanks Mark, and you very well may be correct. I must admit, I did not do the work when done on my car, but according to the indie that did do it, I was told either one would bolt up. Now if that entails a little modification to get the mechanical to fit when you originally had the hydraulic...i cannot say for certain.
 
#35 ·
Wow. This is a little like a spy looking at grainy pictures of satellite photos; you have to know exactly what to look for.

With a mirror and flashlight, at high noon, looking down on the engine, I was able to see the two upper pulleys (or rollers or whatever they are), both of which had the ribbed serpentine belt on them backward (i.e., ribs outward) and one of which had an off-center bolt on its face.

Buried in between the belt going in and out of those two pulleys, I noticed in the mirror a dime-sized raised outside hex casting with a hole in the center.

Am I correct in these two assumptions:
ASSUMPTION: The pulley with the off-center bolt is the idler pulley?
ASSUMPTION: The raised dime-sized hollow hex casting indicates a mechanical tensioner?

NOTE: Picture references:
- hydraulic vs. mechanical tensioner
- Replace Pulley or Entire Tensioner?
- Changing mechanical tensioner to hydraulic
- OEM BMW E46 Belts/Tensioners Replacement Kit!
- Serpentine belt for 318 ti 1997
- Power steering belt tensioner 02' e46

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B
#36 ·
bluebee said:
Am I correct in these two assumptions:
ASSUMPTION: The pulley with the off-center bolt is the idler pulley?
ASSUMPTION: The raised dime-sized hollow hex casting indicates a mechanical tensioner?

Yes, you are correct.

It is really easy to change them out with the front end off the ground and fan clutch/fan shroud removed. There are plenty of DIY available.

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Click to expand...
 
#37 ·
Taking your advice to get a mechanic's mirror, looking down from the top at high noon with a flashlight, today I determined I have a mechanical upper tensioner (now that I know what to look for) on my serpentine belt.

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#38 ·
Removing the 9 strange philips head screws to lower the engine bottom plate, it was really easy to see that the A/C belt tensioner was also mechanical.

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