Captain_Slow

My ps pump had been moaning at start up since weather started getting cooler. Last weekend I replaced the reservoir and supply hose from reservoir to pump. The pump still makes noise until the fluid warms up. Today I took the 928 for a long drive and all was well. But when I returned home and popped the hood I noticed the new reservoir was wet along the lip running around it where the band clamp holds it in the bracket. Fluid level is correct (before and after drive). I'm sure the fluid is foaming (I've observed the bubbles in the reservoir after driving). I'm guessing the foaming is creating an overfilled condition, under pressure, and causing the fluid to be forced out past the cap seal. Anyone have a better explanation?

I will replace the ps pump with a rebuilt spare that came with the car. Before I do I want to be sure there are no other possible restrictions that could cause the brand new reservoir to overflow while driving.

Jon

Mrmerlin

do you have the lines correctly connected to the bottom of the reservoir?
thats the only thing i could think of , otherwise a foaming fluid could be a bad pump
What kind of fluid are you using?

Once the system has been bled then the fluid should not foam,
maybe its time to replace the pump.

The fluid level should be close to just above the seam in the tank

Captain_Slow

I'm pretty sure it's the pump, but just wanted to be sure I've checked everything. I'm using DOT 3 ATF. I think there is a small leak in the pump body, not at the banjos. Hoses are all on tight. The pump noise goes away after the fluid is warm so it does look like it's a worn pump. My next project. Thanks

heinrich

Maybe water --> steam

Captain_Slow

I guess I should have been more clear -- it was wet with the red ATF fluid.

I'm pretty sure air is getting sucked into the pump at cold start up, with less and less air sucked in as the fluid and the pump warm up (pump body and damaged seal expand). After shut down the pump cools off and fluid weeps out the same small hole.

I'm also wondering if something like the following is going on, to greater or lesser extent depending on how much air is drawn between cold start and normal operating temperature... (or, I'm way over thinking this)

At cold start up the pump complains as it compresses this mix of air and ATF, dissolving the air gasses in the fluid so there are few bubbles (like a soda bottle before you twist the cap off). I'm assuming this because foamed up fluid would not provide normal power assist. Under pressure the mixed in air may remain mostly dissolved in the fluid due to very high pressure in the high pressure lines and within the rack, not foaming until the fluid exits the rack and is again under only atmospheric pressure. This is analogous to a bottle of carbonated soda pop. The CO2 in the bottle remains dissolved until one twists the cap and breaks the cap seal - then viola, lots of bubbles. Given the VERY high pressures after the pump foaming is likely minimal to none until existing the rack. The low pressure return line will likely be filled with a rapidly expanding foam (kind of like shaving creme expanding when it exits the nozzle). This foam gets dumped back into the reservoir where it likely expands still further, thus it leaks out around the reservoir cap seal I guess. So, maybe after the rack the return line and the reservoir get a bad case of the BENDS. Not sure I'm on to something with this, but does seem plausible. I just don't see how foaming fluid could provide steering assist within the rack, so I think the foaming mostly happens in the low pressure return line.

Mrmerlin

yes my head is hurting from all of this thinking,
just put the new pump in and report back