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Discussion Starter #1
The power steering pump on my MK4 is going out. There is no/little power steering assist at idle, but if I give the revs a bump to 1500+, the power assist comes back. I am looking for your thoughts on the cause of failure and what should be done different this time around.

Setup: Mk4, coyote with the ford racing PS bracket and a reman 2005 mustang PS pump. I run hydroboost brakes and an SN95 power steering rack. The fluid was just basic Valvoline PS fluid. The car has less than 7000 miles. I've done a few track days and the symptoms got a lot worse after the most recent track day.

I have a couple thoughts. Looks like ford recommends mercon for the 05-10 instead of plain PS fluid as I was used to on the previous generations. I'll be going back in with mobil 1 ATF (mercon). It should have the additives ford wanted and better temperature resistance (especially on track). Obviously a flush will be in order.

My rev limiter is set to 7400 rpm and I haven't been afraid to explorer those regions, especially on track. The car which the PS pump is from (05-10 mustang) had a rev limiter of 6250. Would that likely cause an issue? Seems to me like it would just bypass more fluid and survive fine, but that's just my gut reaction.

Any other thoughts on what I should do different to avoid another early failure?
 

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I learned on mine years ago that lots of time at high revs superheats the fluid. After a long track session or even some back to back autocross runs I was losing assist. I know the Challenge series guys had the same issue and many changed the pump pulley to slow it down. Problem with that for a street car is that you may run it too slow at low speed to develop boost. Mine always came back after cooling down so I have to wonder if you might have done in the pump---hope not. I added a cooler to mine and give it fresh fluid every couple of years and it has been trouble free since.

Jeff
 

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Anytime you're bypassing fluid, you're creating heat. If you're tracking the car, long straight stretches at high RPM's is going to generate a lot of heat in the fluid. I think you need a good cooler, and a new pump. Use the correct fluid.
 

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Discussion Starter #4
Sounds likely heat is the culprit here. I do have the stock mustang "power steering cooler", but it is essentially a 10' long out and back length of hard pipe, so not a lot of heat transfer going on. I'm not able to put a larger pulley on the PS pump. The current pulley is a 1/4" away from the 4" frame rail. There might be smaller crank pulleys available, but I'd rather not mess with the damper/crank pulley on the coyote as some engine failures have occurred with aftermarket balancers.
I suppose the other option is going to electric power steering with a unit such as the MR2 pump. It doesn't care how fast the engine is spinning. I am leaning this direction as a long term solution and can still add a cooler if required. It'd even free up a couple horsepower from the crank.
 

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I used Derale’s Compact Fluid Cooler, Model #13310. Interestingly enough, I chose this part on my own - and it’s the exact same one edwardb used!

Plumb it into the return line, & mount it in a convenient location (I shamelessly copied edwardb on this one, & chose the side of my radiator shroud).


John

IMG_2715 by jhsitton, on Flickr
 

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I just went with a 4 pass cooler that would fit into the oil cooler scoop. I don't have any specific photos but you can see it here:



I think I'd give that a try before ditching the hydraulic and going to electric assist (of which it's no secret that I am not a fan).

Good luck!

Jeff
 

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I would replace the pump and put the largest cooler you can fit. Based on my experience w/ a 99 Explorer pump on my 351, I would also consider using Honda PS fluid. That fluid alone fixed 90% of my loss of assist at the end of an autocross run. But I have no idea how it fits in w/ the fluids you are getting recommendations for.
 
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