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External automatic transmission fluid filtrationÖ


The automatic transmission produces metal wear particles as a result of normal operation and the associated friction between moving metal parts inside the transmission.  The conventional strainer-type filter normally found inside the transmission is generally not effective in protecting the transmission from the wear resulting from these metal particles and will only capture the large particles (which are less common in automatic transmissions) while allowing the more common, tiny particles (both metallic and non-metallic) to pass through uncaptured.

Itís vitally important that these tiny particles are captured using both magnetic and paper filtration because they exacerbate wear in the precision-engineered transmission when theyíre allowed to circulate in the fluid throughout the transmission.  Automatic transmissions are very expensive to repair or replace.  It makes a lot more sense to fortify the transmission with additional filtration that will capture the vast majority of wear particles than to allow the transmission to wear out prematurely and require expensive repairs or replacement.


The solution is external automatic transmission fluid filtration...

The solution is to install an external filter with magnetic as well as paper filtration between the automatic transmission and the radiator on the hose going from the radiator to the transmission in order to capture even the smallest metal wear particles that would normally pass through paper filtration alone.

This filter should be replaced every six months due to the extremely high workload of the automatic transmission to ensure that it never becomes clogged with contaminants.  This would result in the bypass valve inside the filter opening and allowing fluid to flow through without being filtered.


I use and recommend Magnefine external automatic transmission filters...

Magnefine is a company that makes an outstanding magnetic filter for automatic transmissions for 5/16Ē internal diameter hose as well as for 3/8Ē internal diameter hose.  The Magnefine filter contains:

  • A powerful magnet to trap even the tiniest metal wear particles within the automatic transmission fluid that would otherwise pass through paper filtration.
  • Paper filtration to trap non-metallic wear particles that are deposited into the fluid as a result of the friction operation of the clutches in the transmission and which would otherwise evade capture by the inadequate strainer-type filter inside the transmission.

Tips for installing an external automatic transmission fluid filter...

Itís a pretty fiddly and time-consuming job to install this external filter but the benefits far outweigh the hassle.  Once itís set up and installed, itís easy to replace the filter every six months and it doesnít take much time at all.  Below are some tips for the installation.  Ask your mechanic about installing this filter if youíre in any doubt:

Install the filter on the fluid hose that returns the fluid from the radiatorÖ

The automatic transmission fluid is routed through the radiator and back to the transmission via two hoses in order to regulate the temperature of the fluid and prevent the fluid and the transmission from overheating.  Itís best to install this filter on the hose from the radiator back to the transmission since the fluid will then have already passed through the radiator before entering the filter and will therefore be cooler.  Since the Magnefine filter is made out of very tough plastic, not metal, itís worth cooling the fluid down as a precaution before letting it enter the filter.

Method for determining the direction of the flow of fluid between the automatic transmission and the radiatorÖ

In order to figure out conclusively the direction in which the automatic transmission fluid flows between the automatic transmission and the radiator, itís necessary to disconnect both fluid hoses from the metal fluid pipes to the transmission.  One of these pipes carries fluid out of the transmission and one of them carries fluid into it.  Which is which is what you need to determine.  You can place a drain pan underneath the transmission beforehand to capture any fluid that spills out when you disconnect the hoses.  You can use foam earplugs to plug the ends of the fluid hoses to prevent any further fluid from leaking out.

With the drain pan still underneath the transmission to capture spilled fluid, have an assistant turn the engine on and watch the metal fluid pipes to the transmission to see which one has the fluid pumping out of it.  Even though the transmission is in ĎParkí, it will still pump fluid out when the engine is turned on.  (This is the fluid thatís normally pumped through the radiator to cool it.)  Once you know which pipe it is, have the assistant turn the engine off so that no more fluid is lost.  Record on paper which pipe youíve observed the fluid emerging from.  Itís a good idea to also make a permanent record of this somewhere so that you donít have to go through this procedure again down the track.  The other pipe from which no fluid emerged is therefore the pipe that returns fluid from the radiator to the transmission.

The filter must be fitted into the hose that connects to this return pipe so that the direction of flow which is marked on the filter matches the direction of flow of the transmission fluid towards this return pipe.

Lengthen and divert the hose to provide further cooling of the transmission fluid and to make the transmission filter accessible...

Itís advisable to lengthen and divert the hose that returns fluid from the radiator to the transmission so that the filter is mounted securely in the space in front of the radiator and behind the front grille to catch the flow of air through the front grille.  This results in further cooling of the transmission fluid before it returns to the transmission.  Importantly, it also ensures that the filter is easily accessible when it comes time to replace it.

Use a galvanised, right-angle bracket to mount the filter on to the vehicle...

The filter can be secured to a 2.5 cm wide (1 inch wide) galvanised, right-angle bracket very simply using two largish stainless steel hose clamps around the filter.  The bracket itself can be bolted onto any available vertical body panel between the radiator and the front grille in the middle of the vehicle, by drilling two holes through the bracket and two matching holes through the available vertical body panel.

Secure the fluid hoses to the body panels of the vehicle with cable ties...

Secure the fluid hoses (from the radiator to the filter and from the filter to the transmission) to the body panels of the vehicle with cable ties to stop them from moving around excessively but while also allowing enough free-play since the transmission does exhibit slight movement in the engine bay.  Place larger diameter hose around any sections of these hoses which come into contact with the body panels or any other parts of the vehicle so that they canít possibly wear through over the long term and leak fluid.  It takes very little extra effort to do this.

Re-check the transmission fluid level after fitting the filterÖ

Be sure to re-check the transmission fluid level according to the manufacturerís instructions in the ownerís manual for the vehicle after the filter has been fitted since some fluid would have been lost during the process of installing the filter.  It may be possible to use the volume of fluid captured in the drain pan as a guide for how much fresh fluid to add to the transmission.  However itís important to still check the fluid level at the dipstick according to the manufacturerís instructions in the ownerís manual.



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Copyright 2016 Andrew Mackinnon.  All rights reserved.