I'm about to do a full drain and refill of my transmission fluid and eventually plan on towing a travel trailer, so now is a great time to install a cooler. Finding a Hayden 698, which has the thermal bypass feature, for $43 sold & shipped by Walmart was thus a very pleasant surprise.

Rockauto is a close second at $44.79. everywhere else is at least $10 more.

HAYDEN 698 Fluid Cooler | RockAuto

The Walmart includes shipping too.

I recently undertook a project to upgrade the transmission cooler on my truck and went with the HDA-526, HDA-355, and HDA-3655.

Transmission cooler with e-fan, PWM fan controller, and in-line temperature probe (vs the usual probe inserted into the fins of the cooler).

The Fan Controller allows me to set the temp that the eFan powers on, and being a PWM (Pulse Width Modulation) controller it enables a soft start.

There's also the capability to have the fan power on with the AC compressor to improve the airflow across the condenser if the vehicle is parked. I've not done that, but I'll eventually get a VoSwitch where I'll have a transmission fan cooler button so I can turn the fan on when towing in stop and go or abnormally hot temps.

Fit really well on the passenger side in front of the condenser and installed the controller on the inner fender between the battery, and the temp probe went in an inline brass tee I built in the Home Depot hardware aisle and seems to work well so far.

For anyone here seeking info on installing a Hayden model, I had a couple of questions so I called them and got the answers:

- If mounting horizontally, which is okay per the directions, it doesn't matter whether the incoming fluid flow is into the top or the bottom port.
- The 698's fluid capacity is 1 quart or less, which I wanted to know b/c I'm doing a full drain and fill at the same time I install the cooler.

I'm tempted to buy one since I have one of the hayden non-bypass coolers and it won't get up to temp quickly around town. Then swap out my current non-bypass for the bypass cooler

This is from Hayden’s FAQs in case it helps with your decision:

==
Can you over cool the transmission fluid?

Answer: Transmissions are not highly sensitive to cool operating temperatures. However, in sub-freezing (20-30°F) weather conditions, transmission fluid can actually gel up in an external cooler and cease to flow, causing damage. Use of the radiator cooler actually helps warm the fluid under these conditions. It is critical in extreme cold conditions to use the original equipment cooler in series with an auxiliary or by-pass cooler and allow the vehicle to warm up before driving.
==

I get the concept but how does that functionally work?

Transmission output > Factory Radiator Cooler > Aux Cooler > Transmission Input?

What happens if the Aux cooler bypasses until temps are sufficient then as fluid pressure is applied a gelled slug of coolant gets pushed out of the cooler into the line?

yep mine currently goes out of transmission, into the radiator, out of the radiator into the cooler, then out of the cooler and back to the transmission. I just like that the 698 will temporarily bypass the auxiliary cooler until its up to temp, so the coolant is warming up the fluid in the beginnning

So the Aux cooler with integrated bypass will allow fluid to flow around the aux cooler until up to a certain temperature, then with open flow through the cooler. Almost like a thermostat for trans fluid

I'm not sure but on rereading the FAQ answer, I wonder if they actually meant subzero, not subfreezing, i.e. 20°-30° below zero. I can't imagine transmission fluid gelling at 20°-30° F. I've contacted them and asked so I'll post their response.

I installed the Trucool LPD4544 9”x11”x 3/4” and it does a great job in the summer pulling 3500 boat and not getting above 160*F. But in the winter I need to put a cover in front to allow the tranny to get above 130*F. I cover about 2/3 of the cooler. It has the LPD low pressure drop feature as well. I also switched to AMSOIL trans fluid syn so gelling wont be a concern. It fits below the vertical radiator support.

Tru-Cool LPD Transmission Oil Coolers. Protect Your Investment. | Tru-Cool

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@Drcoffee , where do you live and what are the coldest temps you typically get (not the occasional Arctic blasts)?

Just outside Chicago IL. We get both extremes here living close to Lake Michigan. From -10 up to 100*.
I use a piece of plastic sign board to block it in the winter. You can leave it on permanently if you choose. The cooler is so large and the radiator fan runs 100% of the time. Just pop it off when wheeling or trailering.

“Its better to have and not need, than to need and not have”

I messaged Hayden and they answered yesterday that the FAQ should indeed say -20° to -30° F and they're going to fix it.

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