Seeing as my rig just dinged 300K and I have no reliable maintenance records from the previous owner, I have a mind to manage my pink milkshake of death risk ASAP.I got plans to replace the radiator in the near future but for the moment, I just got my hands on a Hayden 678 for cheap and was wondering if the jury is still out on it being able to handle stand alone transmission cooling (bypassing the stock radiator), I searched through historical posts and got mixed info. Any feedback from current/past users would be greatly appreciated.

If the top of your radiator is olive colored rather than black, then just replace it. You can get one for about $150 at the local parts store. If yours is original the top hose nipple is probably about ready to crumble off.

Cant say much about the trans cooler you have. I just replace the radiator so as to kill 2 birds with one stone.

That's what I'm running on my 01 and bypassed the radiator. I tested it on a steep rough dirt road while it was over 90 out and it never got over 204 degrees (UG trans gauge) then when it did I simply stopped and idled for a single minute and the temp quickly dropped down into the low 190's. Now that it's cold out it doesn't get over 140 and if I'm running around it town it doesn't get over 130 which does concern me so I'm installing an inline trans fluid thermostat that should bring it up to the operating temp of 180 by bypassing the cooler until it does. Not sure if running cold (relatively) trans fluid all the time during the winter will do any harm but I figured for $50 I could just eliminate the possibility.

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I also added the inline filter for added protection.

https://smile.amazon.com/Magnefine-M...DFNN6ARBM245HJ

Your needs/wants/budget may vary...

There are MANY threads on this subject if you try the search on the 1st page.

YouTube

From my experience it depends on:
1) What are typical ambient temps in your area, above 95 often (30+ days a yr)?
2) Will you tow or now?
3) Will you drive/tow thru mountain passes?
4) Repeated stop/go traffic?

During cooler weather it really doesn't matter much unless towing uphills/passes. During summer if you have 2 or 3 of the above going on, its most likely the trans temps will consistently get above 200, perhaps as much as 240-250. If you don't like the sound of that possibility, do as others suggest, go with a bypass for now but when you replace the radiator (you should about every 10 yrs), run it in-line with the external cooler.

You'll have peace of mind knowing the temps will consistently stay under 200 even under towing, stop/go situations.

Luck and enjoy the Runner.

This topic has been beat to death. Do some reading I guarantee if you search you will have an hours worth of reading on peoples views/ options and experiences.

I have the 679 and I haven't seen over 200 since install. HOWEVER, I'm going to swap out with the 699 soon since it has a built in thermal bypass. Better for the winter months. I'm only seeing 120's if I'm lucky on my morning drives.

Thanks for the heads up on those built-in thermal bypass coolers. Looks like the 698 also has it and is a bit cheaper. I'll get one of those for my other 4r since I'll be getting a new radiator for it soon only because I don't know when it was changed out.

Thanks, I dug through some of the older posts but found mixed reviews on stand alone effectiveness. Wanted to get the latest skinny from people who actually own/use one.

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Im in Salt Lake City so temps vary from negatives in the winter to 100+ days in the summer, do tow a trailer every now and then, usually helping friends/family move. Drive up mountain passes regularly in all seasons as im an avid outdooraman/snowboarder. After reading through all this stuff and considering how often im out in the middle of nowhere with my rig, Im leaning towards what you suggested. Last thing I need is for Brutus to quit on me in the boonies.

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If you tow in the mountains and you're set on bypassing completely I'd run a 678 into a 699. I'm estimating just doing some looking, but I believe the 678 has just a touch less surface area than the stock cooler, so it might work for stand alone on it's own but I don't see it working hauling loads in the mountains. You'll want a second cooler for that, or just one big ass one. The 679/699 are the largest generic coolers I've found, but you could find an old 6.0 Powerstroke unit and make it fit. There was a 31 row option and a 37 row Mishimoto unit out there. Probably be easier to just run the second. That's what I plan on doing when I do my power upgrades.