Engine cooling fan blade tips disintegrtating?

[bazar01]

The weather is getting a little warmer so I started removing my alternator for rebuilding. I think whenever I plan on working on something, another thing or two comes up needing attention.
I discovered that my engine cooling fan blade tips are separating at the tips. The blade tips are not solid anymore. It looks like the magnesium material is developing some cavities in the center causing the front and back surfaces to split away from each other along the edge of the blades. Is this common for this model years age?
If I buy a new one ($500) how do you prevent it from developing cracks again?
Thanks for the help.

[aigel]

I have not seen this happen before. Mine disintegrated because I dropped it. The new one is nicely painted and will definitely last a long time, as long as I stay away from it.

Hopefully someone has more experience with a larger set of fans and can post.

G

[bazar01]

I almost dropped mine as well while trying to remove it from the fan housing/alternator assembly that is still inside the engine compartment.
Then I found out the fan blade tips were splitting.

I will take some pics for reference tonight.

[TMc993]

Originally Posted by bazar01

Is this common for this model years age?
If I buy a new one ($500) how do you prevent it from developing cracks again?

While it isn't "common," it does happen every now and then and is well documented. It will probably become more common as these cars age and "wear and tear" gets to even the strongest moving parts.

You're lucky you found it. The results of a blade letting go at speed can be pretty grusome.

Other than making sure you mount and torque the new fan properly and keep the appropriate tension on the belts, there's little you can/should do to maximize longevity. It's a pretty sturdy part and should last for many miles.

[porterdog]

It is actually somewhat common; magnesium corrodes rather easily compared to many other materials. You can paint or powdercoat the new fan, or use a treatment like Gibbs to slow the rot.

I powdercoated mine after filing off the worst of the delamination, but haven't had it apart since to see whether the issue has progressed.

[bazar01]

Originally Posted by TMc993

While it isn't "common," it does happen every now and then and is well documented. It will probably become more common as these cars age and "wear and tear" gets to even the strongest moving parts.

You're lucky you found it. The results of a blade letting go at speed can be pretty grusome.

Other than making sure you mount and torque the new fan properly and keep the appropriate tension on the belts, there's little you can/should do to maximize longevity. It's a pretty sturdy part and should last for many miles.

Yes, quite lucky enough to discover the fan blade splitting before I started driving it again this time of the year.

[bazar01]

Originally Posted by porterdog

It is actually somewhat common; magnesium corrodes rather easily compared to many other materials. You can paint or powdercoat the new fan, or use a treatment like Gibbs to slow the rot.

I powdercoated mine after filing off the worst of the delamination, but haven't had it apart since to see whether the issue has progressed.

Do you know if the blade tips are painted as well as they came from the factory?
Mine looks like the tips were bare metal and not painted.

[porterdog]

I believe the OEM part is raw mag.

[bazar01]

Here is a pic.
This is the worst and there were about 5 blades that are delaminating.

[porterdog]

Yeah, mine was no where near that bad. Best replace it, lest it come apart at nine trillion rpm (which has been known to happen).

[aigel]

The 993 fan is painted from the factory. Here is my new one. Money well spent. It is a joy to pop the rear hood on my car.



I'd imagine the paint goes over time.

Also, what is the ratio crank to fan revolutions on the 993? 2:1? That'd put the fan at 6-10k rpm easily in regular driving ...

G

[bazar01]

Hopefully I will have a new impeller in a week. I will probably spray some clearcoat on the blade tips.

[Cobalt]

Best thing to do is keep an eye on it. The fans suck in debris which damages the paint and leaves the magnesium alloy exposed to the elements. Salts and humidity can do massive damage in short time.

If you see a chip touch it up immediately. They used Zermatt silver code L1 to paint the fans, magnesium valve covers on the 911's 928's 944's and other miscellaneous magnesium parts. Problem with Zermatt silver is it turned goldish brown after being exposed to heat for prolonged periods so matching is not always easy.

[Cemoto]

Originally Posted by bazar01

Here is a pic.
This is the worst and there were about 5 blades that are delaminating.

Bazar, just for a point of reference please, how many miles on the car?

You are very lucky to have caught that. Damage could have cost five times that fan blade.

Regards,

[Cobalt]

Originally Posted by Cemoto

Bazar, just for a point of reference please, how many miles on the car?

You are very lucky to have caught that. Damage could have cost five times that fan blade.

Regards,

Mileage or age will have nothing to do with it. More important questions are how long has the metal been exposed? Is the car garaged or sits outside and does it see winter use?

Magnesium alloy when properly protected will last as long as it has no exposed surfaces. A new fan with a scratch can see corrosion this bad in months if it is continuously exposed to moisture and the elements. I have seen much worse.

Basic magnesium alloys will corrode very quickly when exposed to the elements. There are higher purity mg alloys that will withstand corrosion better however I doubt Porsche uses them.

Here are two coupons one is basic AZ91CT6 on the right and Navy grade AZ91ET6 on the left. Both had gone through a chemical conversion prior to being placed in a salt fog bath for 5 days to simulate 1 years worth of exposure.
As you can see how quickly the one on the right deteriorated. Both started out with machined surfaces and no imperfections. If neither had a protective coating they would have corroded much worse. Imagine what your fan with exposed magnesium edges will do if you leave it wet with winter salts on it for a week or two in a damp garage or outside?

The second picture is under high magnification.

[efhughes3]

This is becoming a little common these days. I think the later fans are not lasting as well as early 911's.

[bazar01]

New fan impeller arrived today.

I still have to rebuild my alternator so it will be a while before I can put everything back together. New front and rear bearings, rear tolerance ring and regulator brushes.

[bazar01]

I have dismantled the alternator down to the bearings last night.
The slip rings just needed a little sanding to remove shallow grooves.
Now just waiting on parts.

Alternator info:
Bosch PN 01 120 468 101
Front bearing: 6303 2RS
Rear bearing: 6201 2RS
Tolerance ring: W110-21 (Wagner PN)
Regulator/brushes:
Total: $55 including shipping from Star Auto Electric, Cornelia, GA

Price was not too bad compared to buying a rebuilt one with core exchange.

[bazar01]

Got the rotor slip rings shaved a little to remove worn section where brushes make contact and also installed the new bearings.

The front bearing housing was a little loose so I will install the 6303-2RS bearing with a coating of Loctite 603 bearing retainer adhesive.

[LouZ]

Ironic! On the way to the office this morning.....BAM! I sheared the Alt shaft right off. I don't know if the fan blade broke, got stuck and stressed the shaft, or if the shaft snapped and then the whole fan bounced around inside of the shroud. There is definite discoloration on 2 fan blades (likelty cracks) and some stress discoloration on the shaft. Root cause will be difficult to determine.

Bazar01, where did you buy the fan? Our sponsor Pelican?