I took my car out for a lapping session last July. It was a hot day and I ended up boiling the power steering fluid on the last session. I swapped in some crappy gas station brand auto trans fluid to get me home since a large portion of the fluid had boiled out.

The power steering only worked in spurts on the way home. I replaced the fluid with mobile1 synthetic ATF and now the power steering works fine until the car is warmed up. At this point it will go in and out as I take on turns.

Before I replace the pump, does anyone have any ideas as to what might be going on?


Thanks!

 

My first thought is that you have air in the system somewhere. As the car heats, the air expands and eventually interferes with the pump. Just an off hand guess though. It must have been one heck of a day for you to boil off power steering fluid. Makes me wonder about stop and go in the Texas summer...

 

I thought it might be an issue with air in the system. When it boiled out the resevoir got low enough to where it could have sucked in some air. I don't now much about power steering systems, but how would you bleed air out?

 

Here's a good how-to from AGR performance. It's a pdf so you can print it out. Seems like a detailed and long process.

 

Wow, that takes some serious work.

Here is the instruction from the service manual.

AIR BLEEDING HYDRAULIC SYSTEM
If air bleeding is not complete, the following symptoms can be observed.
• Bubbles are created in reservoir tank.
• Clicking noise can be heard from oil pump.
• Excessive buzzing in the oil pump.
NOTE:
Fluid noise may occur in the steering gear or oil pump. This does not affect performance or durability of the
system.
1. Turn steering wheel several times from full left stop to full right stop with engine off.
CAUTION:
Fill reservoir tank with a sufficient amount of fluid so that fluid level is not below the MIN line while
turning steering wheel.
2. Start engine and hold steering wheel at each lock position for 3 seconds at idle to check for fluid leakage.
HOT : Fluid temperature 50 – 80°C (122 – 176°F)
COLD : Fluid temperature 0 – 30°C (32 – 86°F)
Recommended fluid : Refer to MA-10, "Fluids
and Lubricants".
Fluid capacity : Refer to ST-47, "General
Specifications".
PGIA0007J
SGIA0506E
Revision: 2007 June G37 Coupe
POWER STEERING FLUID
ST-11
< ON-VEHICLE MAINTENANCE >
C
D
E
F
H
I
J
K
L
M
A
B
ST
N
O
P
3. Repeat step 2 above several times at approximately 3 seconds intervals.
CAUTION:
Never hold the steering wheel in a locked position for more than 10 seconds. (There is the possibility
that oil pump may be damaged.)
4. Check fluid for bubbles and while contamination.
5. Stop engine if bubbles and white contamination do not drain out. Perform step 2 and 3 above after waiting
until bubbles and white contamination drain out.
6. Stop the engine, and then check fluid level.

 

you just turn the wheel left and right to bleed it...

check if the reservoir is clogged (there is a filter at the bottom). you have to drain the fluid from the reservoir first.

IIRC the G35 took ATF for power steering fluid. check the manual (i think it also says on the power steering cap)

 

WITH THE ENGINE OFF.

Turning it with the pump running just recirculates the air.

What needs to be done is to use the piston in the rack and pinion to push the air bubbles out to the pump.

 

I tried turning the steering wheel back and forth (with engine on). I had my son turn the wheel while I checked out the fluid. It ran clear with no bubbles. The resevoir is clear also. I'm going to try turning the wheel with the engine off when I get home from work.

I can't replicate the power steering going out in my garage. It will only do it while driving which is making it hard to diagnose. I've also heard that the acc belt can become contaminated by power steering fluid. This may have happened when the fluid exploded into my engine bay. I've read that the belt slipping can be mistaken for air in the system. I can't really think of anyway to diagnose between the two.

 

I had a similar issue w/ my power steering after tracking my G. The steering seemed to be half there so i took it to the dealer and it turns out the power steering control unit was bad. It was only producing 2.2 V instead of 4.4V. Dealer replaced it under warranty.

 

Ugh... my car is pretty modified I'm trying to avoid having to change some things back to stock to take it to the dealer.

When you say the steering was half there, do you mean it only took half the pressure away from steering the car, or it worked half the time perfect and half the time it didn't work at all?

My issue is the later.

 

the second i guess, so at dead stop it would not help but when i started rolling you could feel it helping a lil bit. By any chance do u have an oil cooler mounted in front of the power steering cooler?

 

I do........ I think that was part of the issue with the power steering fluid over heating.

 

I played around with it more last night in my garage. The system would stop working when I made sudden movements from one side to the other. I aimed a video camera inside the fluid resevoir and turned the wheel to get the power steering to stop working. No bubbles showed up in the fluid. I aimed it at the pump next to see if the pulley was slipping on the belt. No issue there either.

I think that there is a good possibility that it is the power steering control module. The only other thing I can think of is one of the valves in the rack has gone bad causing fluid to not be routed to the correct side of the piston. I think I'm going to be spending the weekend converting the car back to near stock so I can take it in to the dealer.

 

yeah i had the same set up, an oil cooler in front of the power steering cooler, so i took the oil cooler off before taking it to the dealer and they fixed it all up. I originally thought that was the issue until they told me it was an electrical problem w/ the control module but now that it happened to you too i wonder. Do u know where the control module is physically located at?

 

I don't know where it is located, but I'm guessing that overheating is part of the issue. I don't know how the speed sensing power steering works on the G37. I'm guessing it has something to do with the valves in the rack controling how much pressure is released to the piston. The module might be attached to the rack. I'll prolly poke around tonight to see if I can get a better look at the rack.