My son and I replaced all three power steering hoses on his '88 240 (200,000 miles). After replacing the hoses, we added fluid (Dexron III) and worked the wheels from side to side to get the air out of the system.

At first, there was a sort of pink froth in the fluid reservoir but this became less and less as we kept the wheels going back and forth many times while adding fluid to the "cold" mark on the dip stick. Eventually the fluid moving through the reservoir appeared free of the froth and was pretty clear.

Since we did the above procedure, my son reports that the steering makes a noise like a hum or vibration when the wheel is turned. The noise gets less loud as the car is driven a few miles and it gets warmed up. The power steering belt was replaced a week after the hoses were replaced and the noise did not change. The power steering was quiet before we did this work.

Does anyone on the forum have an idea of what might be the cause and the fix for this problem?

Thanks.