Power steering reservoir pressure

2006, 285,000 miles. 3.8 engine. Did the brakes on my daughter’s van a little while ago and when I got done I was doing a fluid check. When I opened the power steering reservoir a very good amount of air pressure burst out and spewed fluid out. I refilled and went on test drive. When I returned I had the same results. This vehicle is not equipped with a power steering cooler like some are. There is no foaming and power steering works as it should. I don’t intend to put much time and effort in this vehicle. It is safe and running great , but high milage. Looking for suggestions on what could cause this. My thoughts would be overheating fluid, but I believe the pressure builds rapidly even on initial start up. Another thought is some kind of air leak on the low pressure side allowing air in and no or minimal fluid out. Time and availability to troubleshoot this isn’t readily available, so I thought to ask for some suggestions on causes for this. I will eventually do a fluid change. The caps are non vented by design. I had in possession an old cap that I had drilled a hole in for vacuum and pressurization, so I put that on for the interim.

All hydraulic systems create heat, oil expands, air inside expands, and builds pressure. It is their very nature and can’t be prevented. Generally caps are vented so the seals in the system don’t become the vents and leak. You can design seals so they hold that pressure and maybe yours are. If it was designed NOT to be vented, those seals would have to be designed to take pressure. The only reason I can think of designing a pressurized system would be to eliminated foaming on the low pressure side.

If there IS a leak, oil would be going out, air would not be coming in as even the low pressure side (the reservoir) is under pressure. My best guess is the pump is worn out and generating a lot more heat (so more expansion pressure) than in the past. I think keeping the vented cap in place is the smart move at this point to avoid the system finding the weak point and blowing PS fluid everywhere.

I think there has been a problem with a screen in the p/s reservoir in this generation.

The pressure relief valve is stuck open, allowing pressure to build the reservoir.



1 Like

If the pressure valve was stuck, wouldn’t the fluid level in the remote reservoir cause the over pressurization? The fluid level doesn’t seem to change.

You are right. I’ve had to replace the one in my 2005. But in this case there is plenty of flow to and through the reservoir.

So far, I’m in agreement with this theory. Not that it matters. I’m just curious because I’ve never seen this before. Also, my 2005 has a P.S. fluid cooler, so there must have been cooling issues. Whether it’s the valve or overheating issue it seems the fix would be pump replacement. That’s not going to happen til pump fails. I will change fluid just because. Thanks for the input.