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I did the bypass at 137k with no symptoms and my fluids looked perfect. At 147k, my transmission failed. Replaced with used transmission, installed temp gauge. Going up normal mountain hills in 2wd with no load causes trans temp to rise to 220 fairly quickly. I pull over before letting it get any higher. Over those 10k miles before it failed I did one pretty light back roads trip and hauled several small trailer loads short distances. I'm in Portland, OR where it's not particularly hot. I'm 99% sure that I fried my transmission by doing this bypass with no added cooler. Thought you guys might want to know.
 

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I did the by-pass when I bought my X about 10 years ago. Had the rad replaced shortly after I got it and also added the second transmission cooler at that time as well. The difference I did, was I split the transmission coolers by adding "tees" so the fluid would go half through one cooler and half through the other. If you put them in back to back so the entire fluid has to go through two coolers, you add that much more resistance to the fluid flow. By splitting the fluid flow, there is less resistance, but twice the cooling capacity since the fluid should take twice as long to flow through either cooler, so it should be more effective than just a single cooler. I've never had any trouble. Still running as the day I bought it. I regularly tow a 3000lb trailer through the summer. 100,000km added and much of that is towing.
 

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I did the bypass at 137k with no symptoms and my fluids looked perfect. At 147k, my transmission failed. Replaced with used transmission, installed temp gauge. Going up normal mountain hills in 2wd with no load causes trans temp to rise to 220 fairly quickly. I pull over before letting it get any higher. Over those 10k miles before it failed I did one pretty light back roads trip and hauled several small trailer loads short distances. I'm in Portland, OR where it's not particularly hot. I'm 99% sure that I fried my transmission by doing this bypass with no added cooler. Thought you guys might want to know.
Had you performed a all fluid change as recommended at 90k? Had you replaced as recommended the rad at 120k as well as fluid change? Fluids are key to heat transfer and have corrosion inhibators. Radiator cores corrode losing heat transfer too as well as bugs getting filtered through the outside . Had your transmission service include filter change? Skipping one or more will all contribute to a early demise. Now I'm off to see what I need to complete another all fluid change
 

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2013 S 4x4 Burgundy
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Hi all, New to this page and to my New to me 2013 X. I'm really confused if I should or shouldn't do the bypass. My X has 70,000 miles and the dealer just flushed and filled the radiator. Please help!
 

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Hi all, New to this page and to my New to me 2013 X. I'm really confused if I should or shouldn't do the bypass. My X has 70,000 miles and the dealer just flushed and filled the radiator. Please help!
No worries for your 2013. The problem radiators only affected Xs up to early 2010.
 

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2013 S 4x4 Burgundy
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Thank you. I guess I pulled off the Radiator Skid plate just to replace the bolts. First item replaced on my New to me 2013 X
 

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I'm wondering what happens to the transmission fluid trapped in the radiator after the bypass? You guys drain it before closing the loop or it stays there? Won't it cause any problem?
 

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2011 PRO-4X
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326 Posts
You should not be doing the bypass unless it is an emergency to basically get you home. Years later after this was "The Fix" it can lead to transmission overheating. The small cooler in front of the radiator is not enough to cool the transmission especially when you are going slow. The bypass is a bandaid not a fix.
The proper fix is a new aftermarket radiator for $150, the Koyo is the recommended one.
 

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You should not be doing the bypass unless it is an emergency to basically get you home. Years later after this was "The Fix" it can lead to transmission overheating. The small cooler in front of the radiator is not enough to cool the transmission especially when you are going slow. The bypass is a bandaid not a fix.
The proper fix is a new aftermarket radiator for $150, the Koyo is the recommended one.
My radiator looks newer than other parts of the car so maybe last owner has changed it. I'm adding another cooler to the system but still have to bypass the radiator. Should I drain the remaining fluid from radiator?
 

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I'm certainly no expert on this, not a mechanic, but I have paid attention to this issue since I bought my X used a couple of years ago. My understanding is that as long as you did not have SMOD -- so no coolant in the tranny fluid, no tranny fluid in the coolant -- you should just need to top off the fluids after you do the bypass. I'd go ahead and drain the transmission fluid from the radiator. Adding an external transmission cooler is a good idea.

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My radiator looks newer than other parts of the car so maybe last owner has changed it. I'm adding another cooler to the system but still have to bypass the radiator. Should I drain the remaining fluid from radiator?
Why are you still doing the bypass? It has been shown that air to liquid is not as efficient at cooling as liquid to liquid. If you are adding an aux cooler, it needs to have a fan on it.
 

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2011 PRO-4X
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As said above it really doesn’t matter how many external coolers you add, at low speeds you are still going to cook your transmission. The issue isn’t the cooler it’s lack of airflow.

Do it correctly and run the trans through the radiator like it was designed and every other vehicle on the road uses.

My cousin builds desert race trucks and ran into the same issue even with huge coolers. As soon as the hit a slow section or got stuck behind someone they would overheat the transmission. They had their radiator fabricator put in a big internal transmission cooler and never had any issues again.
 

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In my 2015 X with bypass I overheated transmission past 260 degrees. With stock setup I never went past 242. Same trail just 2 weeks apart.
 
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