The first time we found this in the line, we spent several hours at the Honda parts service counter with the VIN# from the van. The parts guy could not find it. The replacement cooler line has no filter, and the one shown here was nowhere to be found. As far as Honda parts is concerned this filter doesn’t exist. It wasn’t till a few months later we learned that this complete cooler line and filter comes packaged with a Honda reman transmission. It appears they do not trust that the OE cooler will be adequately flushed, and install this filter to catch any lockup clutch particles. So any vehicle that has had an OE replacement may have one buried somewhere in the line.
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It so happens that this filter can be taken apart and cleaned, but we prefer to remove it altogether since it is a very low capacity filter and even when clean adds additional restriction to the cooler system.
If you prefer to have an external filter installed, that’s a good idea IF and ONLY IF it is a large capacity low resistance filter (about the size of an engine oil filter) that will not drive up cooler pressure when it is 30% plugged. It should have a safety blow-off well under 30 psi.
Many of the 5 speeds have a trans mounted heat exchanger on top of the trans [see figure 8]. When new, they flow a little better than the 4 speed cooler system, but we’ve cut them open to find they also clog up. Unfortunately this bad boy is very expensive to replace, so we recommend using a transmission cooler adapter. The water lines can be joined by a coupler made up of 2 barbed fittings and a straight fitting [figure 9]. These can be found in the plumbing department at Home Depot. The three brass fittings run about $12. The total cost for adapter, cooler, and coupler is still far cheaper than a replacement heat exchanger and the trans will run much cooler with the external system.
Several aftermarket versions are available. Your regular parts supplier probably stocks at least one of the available types. But we have also discovered that Honda also has adapters for many models. There are a few different ones, and the price varies, but overall they are cheaper than the aftermarket ones, so check the dealer first.
In addition, a 1/2” fitting with a hose barb can be installed in some of the cases after the heat exchanger is removed. The case can be threaded with 1/2” pipe tap and the barb screwed into case and then a cooler line directly attached. The return line can be cut and adapted to receive a hose also, so that the OE setup can be bypassed and an external cooler installed.
We have found that the OE cooler system is very restricted. By installing a new external cooler (even the smallest, like a Haydon 1401) and bypassing the OE radiator and inline filter, cooler flow is literally doubled and cooling capacity dramatically increased. This suggests that resistance was cut in half. So if you were to run the new external cooler in PARALLEL with the OE cooler [figure 10], then you would be dropping the resistance to 1/3!
That is, your flow potential would be tripled at the same pressure. But in reality, when at a stop in D at idle, the actual flow delivered to the cooler system is controlled by what is fed to the converter release (front) side, since you can’t get out more than you pump in. This is much lower than the cooler system’s flow capacity, which means therefore that you will effectively lower the resistance and pressure in the cooler system to ensure rear side pressure is always lower than cover side, and in doing so, you have preserved lockup clutch life.
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