Lately, my power steering fluid has been heating up to the point where it will expand in volume enough to escape out the vent in the cap. What could be the cause of this? My thought is the power steering pump is dying and creating enough internal friction to kill the fluid. The fluid is not foamy or opaque, just much less viscous than it should be.

 

I'm not a mechanic to answer this, but I found a thread that is VERY similar to your concern on a Chevelle forum. Read it through and see if this has anything that you can work with
http://www.chevelles.com/forums/showthread.php?t=255808

 

Thanks for the link, it sounds very similar to my issues. I may try the filter/cooler route before tearing the pump apart and see if that fixes it.
On that note, are there any common OEM applications of PS fluid coolers, or is it all aftermarket?

 

You can get any cheap fluid cooler and just adapt the fittings to work. Put it on the low pressure return side!!!
Look for a small transmission cooler. Power steering coolers are a little more exotic, so can be a bit more expensive for basically the same thing.
If you like the you-pull-it junk yards, just go shopping!

Note that it is pretty odd to have that kind of heat up, so something is probably wrong and may go ka-blooey sometime soon. Unless you're autocrossing.

 

I was just wondering when or what happened just before you noticed the overheating? Although PS fluid should be lifetime, it can get filled with contamination too. Does it look black instead of clear or pinky? If it does, why not try a simple fix of flushing the PS and putting in new fluid (Use dexron 3 tranny fluid - it's actually recommended by GM in place of PS fluid - check your owners manual on that)

If the fluid replace works to solve your problem you don't need to do any extra purchases. Dexron 3 is cheap.

 

Fluid replacement would be an easy first step, make sure all the air is out of the system. You may have worn bearings (try sticking a wand magnet into the reservoir to see if you pickup any metal) which could be causing heat buildup, could also be a faulty flow control valve not bypassing at high rpm. Did you make any changes or service the car lately? Any unusual noises from the pump?

 

Well, after installing a new P.S. pump, along with an in-line filter and flushing the system, the fluid in the pump still overheats.
I think i'll be hitting the pick-n-pull and looking for a cooler, and go with that until I can solve this.
Could it be the steering gearbox causing this?

 

Sorry, but your car (and a few hundred thousand like it) did not need a PS fluid cooler when new. First, are you sure you aren't overfilling the reservoir? If not, then find the source of the problem instead of band-aiding it with a cooler.

 

Right now, it's actually below the fill line. I think it may be the pump again, meaning the second defective pump (rebuilt units from NAPA).
Even after I get it working right, I may put a cooler in. I like overkill.

 

Update: After the first NAPA pump failed almost immediately, I swapped it for another and...well, it took a little longer to die, but it was up to the old pump's antics in 100 miles.

I installed a PS filter on the return line, which so far has caught a little bit of crud from the box, but not much. I'm using NAPA PS fluid as well. I'm starting to doubt both the integrity of NAPA's rebuilding services and my competence with power steering systems.

Could it be the Steering box be the problem? As far as I can tell, it's the original unit.