3rd Gen T4R "Pink Milkshake" - How worried should you be? 200k Radiator Teardown

Should you be worried about the dreaded "Pink Milkshake"? I seek to provide some insight.

SUMMARY / TL;DR: I tore apart my original 200k miles radiator for signs of failure that would lead to the Pink Milkshake. I could not find any potential failures. Although a residue was present on the bottom of the radiator, there was no signs of leaking, rusting, on the cooler. A far as I can tell, the radiator was perfectly fine and probably would have last much longer with regular coolant and trans fluid changes.


BACKGROUND: I bought a 3rd gen 4Runner last year with about 192k miles on it. While I was researching the "what to look out for", one of the biggest concerns was the dreaded "Pink Milkshake". The Pink Milkshake is the mixing of the automatic transmission fluid with the coolant/antifreeze, resulting in a creamy and frothy looking pink liquid that circulates thru the transmission and depending on when it is caught may require a transmission replacement.

My question was, how common is this issue? Is this a serious worry? The forums have a way of biasing us, we typically hear the "bad" more than the good. If someone has the issue, they are way more likely to take to the forums than the majority of folks whose radiator is perfectly fine. We typically pay attention to the bad more than the good. If you spend too much reading the forums like I do, you probably run into these general schools of thought when it comes to the preventing the Pink Milkshake.

1. Regular coolant and transmission fluid changes is enough to prevent.
2. Replace the Radiator every a certain interval (every timing belt change, 100k-150k miles, etc.) for peace of mind.
3. Separate the OEM transmission cooler (external trans cooler) and bypass the OEM radiator all together and therefore no chance of the fluids mixing.
4. The OEM cooler sucks and is not enough to cool. Bypass that tiny OEM cooler with large external cooler or put another in series with the OEM cooler.

My T4R is now at 200k miles and overdue for a timing belt job. Before the teardown, I aligned with school of thought number 2: Replace radiator at timing belt change. This is the original radiator that the vehicle was installed with and never replaced. According to the previous owners maintenance records, the coolant and trans fluid was changed before, albeit not at the Toyota recommended interval, but non the less changed a few times in its life.

Now that the timing belt/radiator replacement job is done, I decided to completely disassemble the original radiator, to see if I can find any signs of failure, inspect the overall condition, learn something, and perhaps guide my future decisions on radiator replacement. Come along for the ride.


TEARDOWN:



I only removed the bottom head/cap of the radiator (black plastic). The bottom head is the radiator outlet (cooler side) where the coolant leaves the radiator. The top head is where the coolant inlet (hot side) enters the radiator from the engine. The coolant has already cooled significantly by the time it reaches the bottom. This is why the bottom contains the transmission cooler (heat exchanger would be more technical, but I'll refer to it as a cooler). The head is pressed on with a large perimeter o-ring (more of a square than an "o") that seals the coolant between the head and the radiator. The head is pushed into place and tabs along the perimeter of the radiator hold it together semi-permanently.




With the head removed you can now see the transmission cooler. I don't know what I was expecting, but I thought it would be... bigger? It's just a hollow tube, approximately an inch in diameter. The transmission fluid flows in the space between two thin tubes that was capped off and brazed. The fittings themselves are blazed into each end of the tube shell. The coolant flows through the middle of the tube and around it to exchange heat. The heat exchanger cools the transmission when the transmission is hotter than the coolant. It also warms up the transmission when it is cold (at startup), as the engine tends to warm up faster. This is the advantage of having the trans cooler in the radiator, the trans fluid gets to operation range much quicker.




I was a bit alarmed to find some pinkish sludge at bottom of the radiator head, right by the trans cooler fittings. My initial thought was a small leak had formed in the trans cooler, which mixed with the coolant. However, no oil was noted in the coolant prior to this, and the sludge wasn't oily, mostly slimy and gritty. You can see a comparison of the oil vs the sludge.



Just to be sure, I conducted a leak test. I pressurized the trans cooler with 30psi of compressed air and sprayed the whole thing with leak check fluid (not just soapy water, the good stuff). No leaks were found. Phew.









I removed the thin nuts that were holding the trans cooler to the head. They were rust seized so I used an impact gun on them. Unfortunately the force of the impact slightly twisted the cooler that you can see in the photos after it is apart. I was surprised to find it still held pressure despite the twisting. Once I had the cooler out, you can see the sludge buildup. It felt grainy, almost like sand. Perhaps from various casting that are on the engine? I'm not too concerned at this point.






You can see how cooler seals with the radiator (see sketch for reference). There is a small o-ring that sits inside the radiator that seals the cooler against the inside wall of the radiator head. On the outside, the thin nut bears down on a washer and a rubber gasket against the outside wall of the radiator head. This would not seal, as any liquid could potentially pass thru still via the threads of the nut. I think the rubber gasket was added as a "isolator", acts as a cushion to prevent the metal washer from bearing directly on the plastic, and adds some debris/water resistance to the fitting.



I probed the trans cooler with a magnet, the fittings are some sort of steel, whereas the cooler tube is non-magnetic, perhaps stainless steel as some grades are non magnetic. I did a quick grinder test on the fitting and the tube material, both produce sparks (aluminum does not).





I cut open the cooler to see what was inside and inspect for corrosion. It was interesting to see a metal mesh inside the space of the two tubes to aid in the heat transfer from the fluid to the tube shell. No signs of corrosion were found inside the tube.


QUICK DISCLAIMER: This is in no way a scientific study, more of an inspection. This is only one data point and not enough samples were taken to draw an reasonable conclusion across all vehicles still in service.


THOUGHTS: I was expecting to see some sort of degradation of the cooler, and surprised to find nothing that would lead to a mixing of the fluids. I was surprised to see how small the exchanger was. The only signs of corrosion were of the outside of the radiator, were the send and return line fittings thread into the cooler. The trans cooler is pretty well contained, and would only mix with the coolant if the portion of cooler inside the radiator fails (ie, the tube, brazed joints, material corrosion).

I have heard in the past that an "o-ring" is the only thing that separates the trans fluid from the coolant. This is not true. If the o-ring fails, coolant leaks to the outside of the radiator, and does not mix with the transmission fluid. Theoretically, if the fitting on the outside failed in just the right area, I could see the o-ring becomes the only thing holding the fluid back from mixing with the coolant. If that is the case, I would expect to see some trans fluid leaking to the outside of the radiator as well. See sketch below:




CONCLUSION: Based on my findings, I am much less concerned about the Pink Milkshake. The 200k mile cooler was nowhere near failure. If I had to guess, the failures reported before where either due to high levels of salt intrusion, poor maintenance causing acidic coolant or trans fluid that degraded the cooler, or tiny portion of manufacturing defects which lead to premature failure.

Personally, I will not be replacing the radiator at the each timing belt change. Unless I see significant exterior corrosion on the transmission cooler fittings, damage to the fittings, or trouble signs in my coolant (oil in coolant, discoloration, etc). With regular coolant and trans fluid changes, I see the Pink Milkshake risk as very small.


Thanks for reading. Plan to cut apart the trans cooler, post will be edited to update with more info. Constructive criticism welcome.

 

Another very good reason to replace the radiator every ~10 years is that the plastic caps become extremely brittle with age. I've had them literally disintegrate in my hands when trying to remove the upper radiator hose from the radiator outlet.

 

this is a great write up. alot of vehicles have this same problem with the rad. my old armada was the same way.