Excellent information! I plan to flush my system in the next few days and would like to remove the tank for cleaning.Any suggestions as to a solvent to remove stains inside of the tank?
On "solvent" for cleaning the AHC Tank etc, suggest use something similar as mentioned by
@PADDO for cleaning the internal screens/strainers inside the Pump -- or at least that is what I have done:
Previously,
@PADDO made observations at Posts #16 and #19 in the thread below:
forum.ih8mud.com
At this post #19 in the above link, it is noted that:
“The two screens are internal to the pump so the pump/reservoir assembly needs to be removed from the vehicle. It’s then a matter of taking off the circular external pump housing which gives access to the pump. It’s retained to the main body and held together, its a sandwich design, by four cap screws. Undo the screws, and disassemble the pump sandwich and the screens are revealed. They are pressed in and can be cleaned in situ with a blast of 100% hydrocarbon cleaner or you can back them out with a pick to clean. Reassemble, install the pump/reservoir fill with fluid and let it sit for a while to assist the fluid in working it’s way into the pump housing/intake and fire it up. If it times out because it’s airlocked and can’t prime then force run it manually**”.
* in other words, something that dissolves oils and evaporates readily without leaving a residue, so not a detergent.
** means operation of the pump by “Active Test” for about 10 seconds with AHC fluid at correct level or better in the tank, or operation by direct connection of the pump motor to the battery.
If a clean-up is being done, it is worth disassembly to investigate the screens/strainers which are are located inside the pump block, on the input and output sides of the tiny gears (smaller than a thumbnail) which provide the actual pumping action. Gear pumps usually are specified for high pressure / low volume applications where the fluid is free of particulates. The screens/strainers are intended to keep particulates out of the actual pump. Particulates might otherwise degrade or destroy the gear action.
When an AHC Pump is thought to have failed or a relevant DTC such as C1762 is recorded – meaning that pump has power at the motor but the pressure is weak and AHC response is slow – then this is more likely to be caused by clogged screens/strainers than problems in the actual pump, unless the screens are missing or have holes which allow particles to pass into the gears. The pump is small but fit for purpose -- it would take something like a stream of sand to destroy the pump.
Some more pictures of the Pump are found in Post #69 and Post #70 in this thread:
forum.ih8mud.com
The problematic internal strainers/screens (not to be confused with the strainer at the AHC Tank) are shown at Post #70 in the above thread.
As can be seen in the diagram below from the FSM, the main purpose of the pump cover with the big "+" is to contain the pressure which is used to force the pump gears tightly onto the pump body so as to minimise side clearances and minimise fluid bypassing the gears at their sides. There won't be much flow in the space inside this cover but outside the actual pump. It is a natural trap for fluid.
As for many types of oils warmed and cooled over a long period of time in the presence of oxygen and moisture, a gel or sludge eventually will form in traps where fluid is stationary or moves slowly. Some of this gel or sludge may find its way into the pump. If so, it will be caught at the internal screens/strainers inside the pump, with loss of pump output pressure and flow.
So a clean-out is a good idea when there are suspicions about low pump pressure and flow and/or DTC C1762. A source of replacement internal screens/strainers is not known -- they do not appear on commonly available Toyota/Lexus parts diagrams and lists. It is not known which of the Toyota/Lexus suppliers is the actual manufacturer of the AHC Pump.
The screens/strainers could he eased out with a pick -- but carefully, do not want any holes in the mesh. A simple backwash may be a safer approach.
Alternatively, and for peace of mind, replacing the pump sub-unit every 15 to 20 years may not be such a bad idea – especially where long term neglect (infrequent AHC fluid changes and AHC pressure checks) by previous owners is suspected. The pump sub-unit is Part Number 48901-60010 – current price example: Partsouq: USD165.31 plus delivery.
Suggest if disassembling the pump to clean the internal screens/strainers, either leave the tiny gears and their carriers in place, or, carefully mark and photograph their orientation to one another so that they can go back together with gears meshing in exactly the same way. Ideally, replace all o-rings encountered and also the oil seal between the pump and the motor.
Suggest if using a secondhand pump, disassemble and clean the screens/strainers before installing in the vehicle.
