Hello folks,

I would like to introduce myself to the forum by writing something useful about hydraulic fluid.

A disclaimer to start with: I do not own a Crossfire, but I sure like them! I work for (and own) a company that rebuilds hydraulic cylinders, lines, and pumps for almost all modern convertibles. Since we are not yet sponsoring this forum, it wouldn't feel right to refer to our services in my posts until the moderators are comfortable with my contributions, and my posts are not regarded as SPAM. We are sponsoring several other forums already, and it can turn into quite a drain for a small company if one was to sponsor every forum that appeals to us. Thus, I'd like to hang out here for a while before taking the next step. Once we feel that the forum is generating enough business for us, we will be happy to become a sponsor...

The parts that are exposed to hydraulic fluid are the hydraulic cylinders, the hydraulic lines, and the hydraulic pump with the control valves attached. The hydraulic cylinders used in the Crossfire RST (Roadster Soft Top) are obviously quite similar to those used in some Mercedes convertibles. The hydraulic lines and the pump are modified versions of commonly manufactured parts, as well, made to fit your cars.

If you find that your hydraulic fluid level is not within the range shown on the reservoir (attached to the pump), then you have a leak somewhere (the fluid doesn't evaporate), and you have three things to do:
1) Find the leak.
2) Fix the leak.
3) Fill the fluid to the required level.

Correct me if I'm wrong, but it appears that Chrysler is specifying the following fluid for the top:
Pentosin CHF-11S. This is a good hydraulic fluid that is used also in some power steering and self-leveling systems. It can be purchased online in many places, or in some good auto parts stores.

Another fluid that is approved by Mercedes-Benz for systems with all the same materials in it as your Crossfires, is FeBi 02615, along with Mercedes' own fluid p/n A 0009899103. It, too, is also used in power steering and self leveling systems. I would recommend this fluid for Crossfires without reservations. In fact, I recommend it to all of our customers. FeBi02615 is generally a bit cheaper than CHF11S, and the characteristics are practically identical. In Europe, the same fluid is also sold as Aral Vitamol. I suspect that Aral is actually the manufacturer of the three fluids above. It is also sold under the brand name Weyle down under, with p/n 0009899103. These are all called "ZH-M" fluids.

What are the characteristics of a good hydraulic fluid for convertibles?
1) Low viscosity over a wide temperature range (meaning a thin fluid that is easily pumped through the tiny hydraulic lines and fittings even in cold weather). This requires a fairly refined product.
2) No Emulsifiers in the fluid. Emulsifiers would allow water to reach the seals in the cylinders and accelerate their chemical decay. Polyurethane gets "hydrolized" by water. Without emulsifiers in the fluid, any water from condensation will simply collect on the bottom of the reservoir without doing much harm, as long as it doesn't get sucked into the system.
3) Lubrication.
4) No additives that might attack the seals in the system. What might be a good additive for old-fashioned transmissions, is likely a nightmare for your hydraulic seals.

DO NOT used "Stop-Leak" type fluids or additives, as these will make those seals that haven't failed yet disintegrate all the faster. Stop-Leak makes the polyurethane seals in your OEM cylinders swell up at first, possibly seal the system for a short time, and then lead to catastrophic failure of all seals. If you buy new OEM cylinders from the dealer, their life span will be significantly shortened by the presence of such additives in the system.

DO NOT use brake fluid. Old-fashioned brake fluid attracts water. DOT5 brake fluid, which is silicone based, is theoretically okay, but it shouldn't be used in a system that already had oil in it.

I hope this helps,

Klaus

 

I use dot 5 hydraulic fluid in all my systems. This includes my motorcycles, cars and floor jack. 40 years with no failure. including ABS. I got mine free from the lab testing it. The US military uses it exclusively. I do remove all dot3/4 fluids before conversion. no glycol allowed. Residual oil not a factor.Dot 5 is inert. If system fouled...flush it or strip it.

 

Thanks for your input on the hydraulics on these cars.I own a roadster and the system has opperated fine so far.Not sure if any preventative maintenance has to be done on these tops or not.

 

arado,

thanks for the comment. You are obviously a sophisticated mechanic. Indeed, the DOT5 fluid has my weakest "shouldn't" of all the fluids that I listed as "shouldn't use". As I said, it is theoretically okay, and I am aware that the military uses it extensively. It lubricates well, viscosity and heat resistance are good, and there are no additives that should harm the system. If you exchange the oils with DOT5 while they are still clean, then everything should be good. My only concern is with contamination. There are reports that contamination in the residual oil, when mixed with DOT5, will form sludge. That again could clog the filter or provide poor passage through the sub-mm openings in the hydraulic system. I would agree with you that DOT5 is generally okay, unless the system is already contaminated. Maybe you have more insight into the "sludge reports", and I would appreciate such input. I would be happy if I have been too cautious and there is another excellent option!

Keep in mind that FeBi 02615 can be bought online for under $10 per quart plus shipping (I am not affiliated with any fluid vendors), albeit that is no match for you getting your DOT5 for free...

Klaus

 

hsell,

when it's convenient, you should flush the hydraulic fluid. Watch out for deposits on the bottom of the reservoir and get them out. I don't think there is any urgency with your location being in Ohio.

A system that gets used frequently will create some sludge. Friction is actually fairly low in the Crossfire hydraulic cylinders, so there isn't too much metal rubbing off. If the original fluid was clear or only had a light colored dye in it, then you know it's time to flush the fluid once it turns dark.

The reason I am bringing up your location is twofold:
1) Decaying seals contaminate the system. The decay of the seals is a chemical reaction that is basically unavoidable on all Crossfire cylinders. Like most chemical reactions, it gets accelerated with heat. Thus, if you live in a hot climate, the cylinders will fail sooner. The ones that are closest to the outside of the car, where they get the warmest, will normally fail first.
2) The other factor in hot climates is that hot air holds more moisture. That is a problem for the system, unless you live in the desert. While the system is in use, the fluid level in the reservoir will change. Thus, air gets sucked in and pushed out. Hot air being sucked in can lead to condensation. Move your top hundreds of times once a day on a hot, humid afternoon, and you will clearly be collecting water in the reservoir. As I mentioned in my first post, water destroys the OEM seals. Let's put it this way: if you were in Jamaica, then I wouldn't be surprised to have you on the phone tomorrow, telling me that the OEM replacement cylinders are already failing again.

Please do not let my comments shy you away from using the top - it is generally better to use it frequently or from time to time than never. Enjoy your beautiful car!

Klaus

 

Thanks for the info.Car has never been out in winter and top will be down 90% of time once the weather clears.Do you feel it to be fine to leave it down or to put it up every 2-3 wks.too keep things lubed.Been in storage since November. Car is basically driven on weekends .Thanks again

 

hsell,

thanks for following up. I don't think your system is in jeopardy at all, the way you are using it. To put it into perspective, I have the hardtops on my (MBZ) convertibles for six months, during the rainy season, and I am not worried about the lack of lube.

It is more the extreme climates down South that I'm worried about. In Texas or on some Caribbean Island, I think you can squeeze a few percent of extra life out of the original cylinders by cycling the top at least a few times a year. Then again, folks in hot and humid climates can simply nip the problem in the bud by having all cylinders upgraded before they fail and drip hydraulic fluid into the car... It's the smart thing to do if you are planning on keeping the car for a long time. Hopefully, we can come up with some DIY instructions for removal and re-installation of the hydraulic system components at some point, so that the undertaking of swapping cylinders becomes an affair that an average DIYer does not have to fear. (Any forum member with experience in writing DIYs interested in taking this on, without money exchanged in either direction?)

Moderators, please contact me if I'm going too far here. On some Mercedes roadster forums, the hydraulic issues used to be most feared, and a good set of DIY instructions together with me answering hundreds of questions really helped the sites and mostly the readers who all inevitably were going to face the issue of leaking cylinders sooner or later. For example, shops used to be able to charge over $2000 in labor for swapping twelve cylinders in the fairly complicated system of the 1990s SL-Class roadsters, where most owners now do the job themselves with a detailed set of instructions in hand...

Folks, please don't worry about the hydraulic system being terribly complicated - it is well designed, requires fairly little maintenance, and those parts that fail eventually are failing in all other modern convertibles, as well. Frequent use will not harm the hydraulic system. If you cycle the top several times daily in a hot climate, simply count on taking care of the hydraulic fluid every few years.

Enjoy the great feature of having an automatic top - it's there to be used!

Klaus

 

Ours aren't automatic.

But Rudy fixed that!