I was about ~2 miles into a trail run yesterday trying out my new front suspension when I lost PS. Looked around and noticed that the truck had quickly puked out all of the PS Fluid. I strongarmed the truck to the closest dealer (that thankfully is really cool about modded trucks), and the verdict is a PS pump failure. I did a little digging and this type of thing has also happened to some lifted FJ owners. Some of them are now running PS coolers as a preventative measure. Thoughts? Similar experiences?

The lifting has nothing to do with it but the bigger and heavier tires and wheels do. Your PS system will run at a higher pressure and your demand will need the same flow so in essence your PS pump has to produce more power as PSIXGPM/constant = power. More power is more excess heat. On roads you should have no issue. Off road a cooler will help a little but you really need a heavier duty PS pump if one can be found. If a cooler is the best you can do then do it!

Better bring a spare to VOT

well that sucks.. maybe i'll add a cooler for mine after i do my trans cooler

Looks like between $170 and $215 to replace with a remanufactured part (rockauto.com). I've not found any details on the unit, so it's hard to find a upgraded unit. You might try emailing Summit, or email PowerBlock - Extreme 4x4 at [email protected]

Okki

Thanks guys. I think the dealer is going to do the repair, either under warranty (shockingly), or at a discount (for an unrelated inconvenience they've caused in the past).

Will update.

Out of curiosity did you happen to get a good look at exactly how it sprung a leak? Did the heat melt something on the P/S pump?

Glad to see the dealer is working with you to resolve this, hopefully its not going to cost you anything!

I haven't gotten a chance to check it out closely as it is still on the truck. The dealer did day that it was not an "abnormal failure". I've heard that the fluid gets dirtier with age and you can overheat/foul the fluid which isn't good for the pump. FWIW I'm at 70k miles, been running 285s for. 40k miles, and have flushed the PS once at about 45k miles.

Good news! The PS Pump replacement is going to be covered under warranty. I guess that Toyota platinum warranty is good for something...

Considering what you do to your truck, 70k on a PS pump is a good show.

If you still have space under the hood, you can use the smallest size transmission cooler for PS cooling. Just be sure to put it inline with the return line, and not the high pressure line. Most PS fluid coolers are actually just a metal line run in front near the bottom of the radiator - the last time I saw a real one was on a Chevrolet Caprice Interceptor.

For an upgrade, have a look if the Tundra PS pump mounts the same, but for all I know all the truck PS pumps are the same unit with different mounting configurations.

One would think all that dirt and mud in Ben's engine compartment would seal any and everything.

I pm'd Ben to ask if he wanted me to do a little write up on PS pump failure that hopefully would help some of you understand more details of this failure. He said sure! So here goes:

The 4Runner power steering system is a simple, closed loop hydraulic circuit. There is nothing fancy here. A fixed displacement pump is driven by the engine to provide power to steer the vehicle. So, if it's so simple, why would one fail after 70K miles?

As I have not torn down the failed unit to provide a precise answer I would like to talk in more general terms. Hydraulic pumps in general fail from:
1. Initial defect (very unlikely)
2. Fatigued components (again unlikely)
3. Loss of seal integrity (probable)

So the first two options are very unlikely due to only 70K miles and the general reliability of Toyota components. This leads us to loss of seal integrity, or a blown internal seal. Why would a seal blow on this truck?
It could again have been a defective seal but if that were the case then it would have blown long ago. The probable cause is this application is the severe duty cycle of this specific application.

A 4Runner's power steering system was designed to provide assisted steering within a set of values. This means:
1. Certain pressures in the system (pressure is force in hydraulics)
2. Certain flows in the system (flow is speed of actuation)

OK 1engineer, so what happened? Well, let me explain a few things first.
Pumps produce flow at a pressure. Put those two things together and divide by a constant and you get power. Any increase in either flow or pressure and you require more power. Ben is an avid off roader and has installed larger tires. Larger tires require more force to turn them so it is probable that the higher pressures, coupled with heat generated by the extra work from the power steering pump, caused a high pressure (relatively speaking) seal within the pump to fail.

What happens is this:
When pumps are pumping, that is producing flow under pressure, heat is generated. When heat is generated, the viscosity of the fluid changes. In this case the viscosity will cause the fluid to be "thinner" and what were once tight seals at a "thicker" viscosity are now loose and a leak path is formed. Once this path around a seal is formed (think of a pinhole gradually getting bigger by erosion) it becomes progressively easier each time for fluid to leak through, or "bypass" the seal. Now oil is like everything else and will follow the path of least resistance, and it's easier for the oil to "leak" past the seal than it is for it to be pumped under pressure to the cylinder. The cycle continues until the seal has a catastrophic failure and dumps all the fluid at once or gradually the pinhole in the seal widens until more fluid is leaked than pumped. This happens over time though so Ben had a quick failure.

Now, was it contamination or heat that caused this failure? I would bet on heat, unless he introduced contamination into the closed system when he flushed the system. I would also say that off roading as much as he does speeded the demise of the PS pump as the constant turning up against rocks, mud and dirt will require much higher pressure than turning on a paved surface. This, coupled with his larger tires, was the most likely failure cause. I cannot be 100% sure but it's a safe bet.

Off roading takes a toll on vehicles. The 4Runner is more robust than most for this type of duty but there will be reduced life expectancy of components when you off road a lot. His idea of putting a heat exchanger on his power steering circuit will help quite a bit. It will keep the fluid cooler and reduce the chances of internal leakage. The best option would be a higher performance pump but I do not know if such a component exists for our 4Runners. Anyway, thanks and hope this helps.

Glad to hear that you're being covered under warranty, sounds like an extremely reasonable dealership

@homeyclaus or @1engineer can either of you comment on if one could potentially "over cool" their p/s fluid? I've read about how you need to size your ATF coolers appropriately and I was not sure if this might be applicable to p/s fluid as well?

Based on what Greg is saying, it seems like during normal on road driving you'd probably not be heating up the fluid too much, so I am wondering if there would any potential negative effects when not pushing it off road?

The oil used is generally automatic transmission fluid or a formulation very close to that. There are enough additives and now synthetics that keep viscosity in a fairly narrow band for the lower 80% or so of operating temperatures. Below operating temperature, it will definitely begin to thicken, but remember this stuff is much, much thinner than motor oil, and have pour points below -40C.

In most normal driving you'll only drop the PS fluid temperature a few degrees, so unless you're in the arctic (or Minnesota), you're really not going to hurt anything. Some statistics claim that you increase component life by about 3% per every degree reduction of a hydraulic oil, although this is most certainly a non-linear graph.

@1engineer one other factor reducing the seal life is constant exposure to mud, grit, or other fine silica, especially when an engine is pressure washed and stuff. That will eventually work itself in there and cause a leak. In my old 4Runner's case that was the front main seal. In joneseyy's case it's this.

Yep you can't really over cool PS fluid unless ambient temp is really low to start with as @homeyclaus stated. Pressure washing is a no no in anything with a shaft seal. Shaft seals usually have an outer dust cover and the seal itself is a case pressure (low pressure) seal which means if the pressure of the water trying to get in is higher than the case pressure then the water, along with the fine particles will win! Good point Homey. Maybe we should post this over on your forum. Oh, that's right, they wouldn't understand because we use words larger than two syllables lol! JK. They have you to interpret now!