There are two types of people out there: those who love a good mystery, and those who just don't have the patience to solve them. Odds are pretty good that, no matter how much you might have liked Poe, Doyle or Baldacci while reading in your living room, you will quickly find yourself short of patience while staring at the foaming power steering pump in your Taurus. So, how do we solve the Mystery of the Frothing Bull? By just cutting to the last page.
The Taurus' power steering system is just as subject to failure as any other, and can manifest in all the same ways. A loss of power steering assist, particularly at idle, fluctuating assist power, pronounced power steering whine and engine laboring while turning hard are all classic symptoms. A wobble in the steering wheel while you're holding it still at an angle; thumping or clunking, and leaks under the car are more likely the rack or the lines than the pump. A car that nearly dies when you turn the wheel may be a sign of a bad bypass valve in the pump. These are all standard symptoms.
All cars have their strange little quirks -- odd failures that seem to affect them for no discernible reason. Frothing power steering fluid that seems to "boil" out of the pump reservoir, combined with fluid that seems to "disappear" after the engine is shut down, are commonly reported problems with Tauruses of this generation. Often, it happens after a pump replacement, fluid flush, or just a refill after a minor leak.
In this case, as in many others, frothing fluid is the result of air trapped in the lines getting emulsified in the fluid; think of this emulsification as the same thing that happens when you shake a bottle of Italian dressing. The oil and vinegar emulsify, turning the dressing milky and opaque. What's happening here is that air trapped in the lines -- either because of an improper bleed after service or because the fluid level got too low -- got mixed into the fluid in the pump. The pump churned it up, making it frothy. When the engine shuts down, some of the froth settles, and the fluid level seems to drop. This isn't uncommon on most cars when pump fluid runs low, but it seems to be a persistent problem for the Taurus.
When this frothing occurs in most cars, it usually isn't difficult to get the air out. You need only wait about 10 minutes after the engine has been shut off for the bubbles to rise out of the fluid, turn the steering wheel lock-to-lock about 10 times with the engine off, and then spin the pump pulley over by hand for 30 seconds after removing the belt. This seems ineffective on the Taurus, though. Perhaps it has something to do with its fluid, the particular architecture of its pump, rack and lines, or the location and condition of the fluid filter in the low pressure line. It may be a combination of all of them. Either way, air has proven very difficult to get out of this system.
According to owners who have attempted it, the standard DIY approach to bleeding the power steering system is largely ineffective. Some have had success with replacing the filter on the low-pressure line; when clogged, it could keep the system pressurized, keeping bubbles in suspension. The go-to solution to this problem, though, is a vacuum bleeding. This procedure involves connecting a vacuum pump to the top of the reservoir, and bleeding the system as you would at home, turning the pump and sawing the wheel back and forth. The vacuum in the reservoir helps to pull the bubbles out of suspension, causing them to rise to the surface. If the vacuum pump doesn't work, or it won't hold a vacuum, you may have a leak in a low-pressure area of the system that allows air to constantly re-enter the fluid.
If, after you've vacuum bled the system, ensured that the power steering fluid is fine and that there's no air trapped anywhere, you still have power steering problems, then it may be time to examine the pump itself. As mentioned earlier, a bad power steering pump will typically whine, fail to deliver steering assist when needed, or deliver it inconsistently. It can be difficult to tell whether or not the problem is in the pump, or the rack; leaking rack seals will bleed off pressure, mimicking the effects of a bad pump. But if the rack seals are shot, the increased effort should be more or less consistent. If the engine seems to struggle when you turn, or is steering effort rises and falls with engine rpm, then the pump is most likely in need of replacement.
