This is a much under-appreciated fact of life with hydraulic fluid. It is the reason why hydraulic fluid reservoirs are transluscent. You can see the fluid level without opening the reservoir and exposing the fluid to humidity.

 

I change mine every oil change, and it is a medium brown tint by then.

I flush it until it is clean, usually about 3 or 4 times. I use the Prestone fluid, and buy a new container for every oil change.

I also put in a bottle of fuel injector cleaner in the gas every oil change too.

 

As this horse lies bleeding on the ground, I thought I'd add just one more tidbit to further your point.

07-07-31-001A: Clutch Hydraulic System - New Service/Owner Maintenance Information - (Sep 11, 2008)

Subject: Clutch Hydraulic System -- New Service/Owner Maintenance Information

Models: 2005-2009 Chevrolet Corvette (Including Z06 and ZR1) with Tremec 6-Speed Manual Transmission (RPOs MM6, MZ6, MH3)

This bulletin is being revised to update the models to 2009. Please discard Corporate Bulletin Number 07-07-31-001 (Section 07 -- Transmission).

This bulletin is being issued to provide dealers with additional information on servicing the clutch hydraulic system.

Please also advise customers of this new maintenance information.

Some cases have been found where the vehicle's clutch hydraulic system was contaminated with water.
Higher than expected levels of water in the clutch fluid greater than 2% may cause the clutch fluid to boil.
The presence of water in the fluid lowers the boiling point significantly; when this occurs, the driver may lose customary clutch pedal feel and performance.

To eliminate the opportunity for moisture to enter the clutch hydraulic system:

• The clutch fluid level inspection should be a VISUAL inspection only.
Look through the transparent reservoir and observe the fluid level.

Avoid removing the cap !
DO NOT remove the cap just to top-off clutch fluid. Leave the system closed and sealed.

During PDI inspection or routine service, the cap should not be opened for just an inspection.

• Open containers of DOT 4 clutch fluid have a two week shelf life.

DO NOT use fluid if the container opening date is unknown or older than two weeks. DO NOT mix or re-use old fluid. Current service information already covers the issue of reuse.

• To provide the best clutch operation, it is recommended that the owner change the clutch fluid every two years.

Please flush and replace with P/N 88958860 (P/N 88901244 in Canada) or equivalent DOT 4.

 

I do the ranger on mine about 5 times suring the forst 5k and then about once every 5k after...Never gets black now. I also do the brake reservoir as well once a year with Dott3.

 

I came across this information and thought I would share.

How fast does brake fluid absorb moisture?

It depends on the fluid and environment. A typical high performance DOT 4 fluid like, Motul, AP, Castrol SRF, Wilwood and ATE SuperBlue, in a high humdity evironment will absorb as much as 4.5-5% moisture in as short a period as 2 weeks. In real world testing (several daily driver cars, Prospeed GS610™ absorbed <1% moisture in 3 years. This was measured from the brake fluid in the resevoir where the vehicle's brake system is most likly to contain the greatest contaimination of moisture.

How does brake fluid become contaminated?

Water/moisture can be found in nearly all brake systems. Moisture enters the brake system in several ways. One of the more common ways is from using old or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from the surrounding air. Tightly sealing brake fluid bottles and not storing them for long periods of time will help keep moisture out. When changing or bleeding brake fluid always replace master cylinder caps as soon as possible to prevent moisture from entering into the master cylinder. Condensation, (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind an increase in moisture/water. Over time the moisture becomes trapped in the internal sections of calipers, lines, master cylinders, etc. When this water reaches 212º F the water turns to steam. Many times air in the brake system is a result of water that has turned to steam. The build up of steam will create air pressure in the system, sometimes to the point that enough pressure is created to push caliper pistons into the brake pad. This will create brake drag as the rotor and pads make contact and can also create more heat in the system. Diffusion is another way in that water/moisture may enter the system.

Diffusion occurs when over time moisture enters through rubber brake hoses. The use of hoses made from EPDM materials (Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR use stainless steel braided brake hose with a non-rubber sleeve (usually Teflon) to greatly reduce the diffusion process.

 

When you purge the system and you pump the clutch 20-30 times don't forget to put that damn cap back on the reservoir! Ask my dumb azz how I know its a birch to clean you engine bay of that fluid!

 

3 of us....

 

Makes me feel better....lol

 

First of all, water (moisture) does NOT separate from the brake fluid unless it becomes saturated. Second of all, if you open the reservoir to remove all fluid there, and replenish it with new one, you have nothing to worry about. And finally, not everybody lives in humid climates. Today we had 5% humidity here in west TX. I could leave the reservoir open all day, and wouldn't have to worry about moisture in my brake fluid . But your point that brake fluid is hygroscopic (readily absorbs moisture) is a valid one .

My final point is contamination can be as bad as moisture, and the only way to get rid of both is with a FULL BLEED job, not just the reservoir. DO NOT procrastinate longer than 2 years on that folks. But sooner, especially the first time, is highly advisable.

 

4 now

 

Well I must admit that this is one brain fart that I have avoided, how I will never know.

It sets up for me to mess up making more of a mess.

Brake fluid being as corrosive as it is has me very focused when using it.

 

Maybe the new C7 will have a bigger capacity reservoir and make the Ranger method much easier.

 

I don't worry about it much, and change the reservoir from time to time, but know this can become a problem. Guy in our road track group with a C6, wasn't aware of this, and his clutch pedal stuck to the floor. Gave him a syphon tool and GM fluid, but his fluid was a black, thick mess. Seems there's a restrictor in the hydraulic clutch return line, to slow pedal action down. When this plugs, well guess we know. Had to get going for long drive, and last I recall, guy was working at removing the tranny tunnel cover.

 

I changed mine immediately when I first read Ranger's post. It took a few times but now it seems to stay clear for at least a year. I changed it last week (after one year) and it was still clear. I use the Prestone DOT 4. My car has nearly 37,000 miles; 2008.

 

I heading out to the garage to change mine right now. I did watch rangers video.

 

It's been a couple years for me, so I guess I'll put it on the schedule in the next week or so.

 

What is the ranger method?

 

 

Just finished changing clutch fluid with Rangers method. Everything went real smooth. My fluid was very dirty.
Once again, thanks to the forum for educating me on clutch maintenance.

 

I bought an automatic . Booyah !