Stop topping the reservoir up and let it find it's own level.
The capacity of the system doesn't change, only the volume of the fluid changes. Change in volume is due to two things:
1. Adding fluid
2. Increase in temperature.
In a stock set-up, the reservoir is designed to accommodate the change in fluid volume over the full temp range. If you fill it up to the top when cold that is too much fluid. As the fluid heats up and expands, the volume increases and will raise the level in the reservoir. That is why the cold level is lower on the dipstick than the hot level. If setting the level when cold, be sure to use the lower mark.
A cooler actually intensifies this effect. The connecting hoses and cooler tubes increase the system volume substantially. This excess volume was not factored in when the size of the reservoir was designed. The cooler does not have the heat exchange capacity to keep the fluid at ambient temperature (it just keeps it from overheating). So, any cooling effect that the cooler has on the fluid is overridden by the increased volume due to the hoses and cooler tubes.
But if you are already aware of all that, read on.
Assuming you have hydro-boost brakes? If so, have you done a complete bleeding procedure?
When you have hydro-boost brakes (and especially with a cooler incorporated into the PS system), it is critical that the bleeding process is done correctly (see below).
Also critical, is the location of the cooler in relation to the other system components and (this is key) how the inlet and outlet hoses are connected to it. Schematically speaking, the cooler should be located either:
1. Between the P/S pump outlet and the hydro-boost inlet or
2. Between the hydro-boost outlet and the steering gear inlet
Whichever line the cooler is inserted into, one thing is important - the flow through the cooler must be like this:
In from the bottom, up through the tubes and out from the top. This arrangement ensures that the cooler tubes are always flooded with fluid and eliminates the possibility of any air pockets forming.
If the hoses are connnected the opposite way, reverse them.
First bleed the Hydro-boost system as follows:
a. Fill power steering reservoir to proper level and allow vehicle to sit for approximately two minutes.
b. Start engine and allow to run for several minutes, then shut engine off. Correct fluid level as necessary. Do this several times until fluid level becomes constant.
c. Raise and support front of vehicle, then turn wheels lock to lock. Shut engine off and add fluid as necessary.
d. Lower vehicle, then start engine and depress brake pedal several times while turning steering wheel lock to lock.
e. Shut engine off, then depress brake pedal 4 to 5 times to allow accumulator to deplete.
f. Check reservoir and refill as required. If fluid is extremely foamy, allow vehicle to sit for several minutes, then repeat procedure above.
Then bleed the P/S system as below:
You must be registered for see images attach
