[gaswede]

I've done a lot of reading on strawberry milkshake on 3rd gens and the preventative maintenance needed to avoid this. My 4th gen needs new trans hard lines up front so i started reading about just bypassing the radiator cooling reservoir all together with an external heat exchanger.

I don't tow nor do mountainous terrain.
My rig was from Chicago but rust is minimal and undercarriage well maintained by the PO.
I exchanged all my fluids after purchase a year ago.

[eleven14]

Originally Posted by gaswede

I've done a lot of reading on strawberry milkshake on 3rd gens and the preventative maintenance needed to avoid this. My 4th gen needs new trans hard lines up front so i started reading about just bypassing the radiator cooling reservoir all together with an external heat exchanger.

I don't tow nor do mountainous terrain.
My rig was from Chicago but rust is minimal and undercarriage well maintained by the PO.
I exchanged all my fluids after purchase a year ago.

What year is your 4th gen? v6 or v8? The 03-05 v6s are notorious for head gasket failure, Toyota remedied this in 06-up. Other than that, I haven't seen much (any) issues with the 4th gens.

[RivMan]

I've never heard of a 4th gen having a heat exchanger failure like the 3rd gens frequently see. The front hardlines rotting out is extremely common though. I chose to replace mine with OEM (~$70) and add an external cooler as well.

Thanks
-Rob

[AuSeeker]

Originally Posted by gaswede

I've done a lot of reading on strawberry milkshake on 3rd gens and the preventative maintenance needed to avoid this. My 4th gen needs new trans hard lines up front so i started reading about just bypassing the radiator cooling reservoir all together with an external heat exchanger.

I don't tow nor do mountainous terrain.
My rig was from Chicago but rust is minimal and undercarriage well maintained by the PO.
I exchanged all my fluids after purchase a year ago.

While there are a few 4th Gens owners who have replaced their radiator because of a small leak after 100,000s of miles but I haven't read of any that had the radiator fail and allow coolant into the transmission.

As far as an external transmission cooler, it's a great idea but I wouldn't bypass the cooler in the radiator, IMHO you can't have enough cooling capacity for the transmission, heat is the number one killer of transmission fluid and thusly transmissions.

[Berty_K]

I've replaced my radiator and added a external transmission cooler. Bypassing your radiator if you have an external transmission cooler is not recommended. Better to run in series to maximize cooling.

[gaswede]

Thanks guys. I have an ‘07 V6 with 175k.
Sounds like I’m on the right path with the hard line replacement. I’ll start researching the external cooler to run in-line with the rad.
To kick off my research, should the external cooler be before or after the rad? I’m thinking after. Maybe that would get it down to about 170 degrees.
Thanks for the recommendations!

[Berty_K]

External cooler should come after the radiator.

Some resources for you that helped me.

Radiator replacement & Trans cooler: How To: 4th Gen V6 Radiator Replacement/Tranny Cooler Install | Toyota 4Runner Forum [4Runners.com]

Literature on why and how you should run the cooler in series with the radiator: Looking at 4th gen 4runner | Expedition Portal

Another very helpful DIY for installing the trans cooler: 2006 4.0L Transmission cooler installation, with some pics. - Toyota 120 Platforms Forum

More detailed (personal) opinions about the install: https://www.toyota-4runner.org/3469885-post24.html

[gaswede]

Whoa! Thanks for the links! That’ll save me a ton of time. Lots to read tonight!!!

[AceSpades]

How do we know which lines are after the radiator? Does anyone have a diagram on the direction of flow?

[Piggity]

You don't need to keep it running thru the radiator. I just ran a line between the two connections on the rad to block it off. My transmission lines were rusted and leaking so I had to do something.

I bought a Uhaul external auto trans cooler and ran new rubber trans lines from it to the front crossmember on the front of the truck. I figure I have less failure points now (by getting rid of the rad in the equation) and it should cool better when I tow in the summer.

[AuSeeker]

Originally Posted by Piggity

You don't need to keep it running thru the radiator. I just ran a line between the two connections on the rad to block it off. My transmission lines were rusted and leaking so I had to do something.

I bought a Uhaul external auto trans cooler and ran new rubber trans lines from it to the front crossmember on the front of the truck. I figure I have less failure points now (by getting rid of the rad in the equation) and it should cool better when I tow in the summer.

You can surely eliminate the radiator from the transmission cooling system and just use an external cooler....BUT it's much better to have both in the system and the transmission will run much cooler with both rather than just one, just because you have rusted lines shouldn't be a reason to eliminate the radiator, replace the rusted lines, all new lines aren't failure points, old rusted lines are failure points!!!