Power Steering Resevoir Blowing Oil out of Cap

[Nobby]

So yesterday start truck and let it idle for 10 mins. Hop in press brake and have solid pedal couple more presses and correct feel comes back. Pop hood and find fluid level low and evidence that fluid was pushed out of the cap and there was some fresh oil leaked out of one of the capped ports of the hydroboost. I suspected a blown hydroboost accumulator but I still have the same amount of residual pressure engine off and the can on the hydroboost is not loose. Hydroboost Unit was replaced 3 years ago so I have a good handle on how much residual pressure there was with it from the get go. After topping up fluid etc all seems OK for now.

Any thoughts as to why the fluid loss. The EVO female connector on the valve is loose which bothers me but I fail to see how a faulty EVO would cause a fluid loss though. I am of the understanding that the system will still function OK with the valve at full flow any road speed.

Cheers
Nobby

[More Power]

Was there an unusual use of the power steering or brakes that happened just before the leakage (for example: turning the steering wheel against a curb)?

Jim

[rustyk]

That's a symptom of low fluid - the pump entrains air and pressurizes it. When the pump stops, the pressurized aerated fluid has no way to release the air, and foams over.

[Liftgate]

My '84 sub has been doing the same thing. I checked the p/s fluid and it was just a little low. Will add more to top it off and see if that helps. :)

[rustyk]

I finally diagnosed this issue on my motorhome, which has a shaft brake disengaged by an actuator pressurized from the P/S system. The actuator was leaking by, and really creating a mess when the engine was shut off.

The issue is worsened because air gets into the Hydroboost, which is the high point in the system.

Replacing the return with a clear hose allows you to bleed the system, but it's tedious.

When the second actuator crapped on my coach, I bled out as much as I could, then drilled a hole in an ATF jug with a sight gage on the side. I then secured the overflow tube into the jug. When the level in the reservoir dropped, the ATF in the jug was sucked into the reservoir. After a couple of foam-overs, the air was all gone.

One advantage I have is that the P/S reservoir on the coach is almost as high as the Hydroboost, so air will migrate there more easily.

[Nobby]

Thanks for the all the responses. After posting I got to thinking about it and as RustyK pointed out she'll burp air if the fluid gets low. So for now I am going to monitor and see if the reservoir level slowly goes down as well as look for leaks

Cheers
Nobby