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Discussion Starter · #1 ·
My 2005 had the catastrophic radiator failure at 159k. First of all, I knew it could be an issue, but I was lazy. To anyone with an original radiator change it... it's not that difficult nor expensive.

Backstory:
I was parked when I noticed the strawberry milkshake dripping out of the front right fender... I called a tow truck immediately and didn't drive. After a 3 hour wait and a 1 hour tow, I immediately drained the transmission and radiator, then removed the radiator. I filled the trans back up with 4 quarts of fluid, connected the two transmission cooling lines together, pulled the fuel pump fuse, and cranked the engine a couple times to hopefully get the new ATF to mix with what ever coolant was left in the tranny. Here is where I stopped for the day. Next I purchased a Denso radiator from amazon and installed it 3 days later. Once installed and filled, I didn't reconnect the trans lines. I left them off and had a helper start and stop the Pilot while I filled the trans up and let it pump the contaminated fluid out cooling line, did this until the fluid looked good. Then I reconnected everything and went for a very short drive. At this point I'd probably gone through about 12 quarts of fluid. After my short drive, changed the fluid. Repeated for another 4 to 5 fluid changes. During the second to last one I added a bottle of Seafoam trans cleaner. Currently the fluid looks good. Fluid wise, I used Valvoline maxlife, instead of DW-1 because of cost doing all the fluid changes. This car has been dealer serviced since new and always has had Honda fluid until now. This weekend I road tested it on a 200 mile round trip drive up to the mountains and I drove it very hard up the mountain. Everything is great through most of the gears, however I'm having an issue:

I'm consistently getting a hard downshift from 3rd to 2nd I think. Particularly noticeable when making a left turn after NOT coming to a stop, the downshift is a hard clunk often times. I realize the trans might act a little different with the Valvoline, but this seems like an issue. Very similar to this to a post here on piloteers titled "2nd Gear Pressure Switch", (Piloteers won't let me at a link to this post)

Is there a good write-up somewhere on pressure/clutch/solenoid/etc switches and sensors, where they are on the trans, and which ones control what? Possibly some troubleshooting? I'm hoping I don't have to rebuild this thing as it might not be worth it. Although if I do I might try to do it myself.

Also, if I was to do this again, I would have drained the failed radiator, plugged the trans cooling nipples on the radiator, filled the radiator, and done the trans flush as described above right away...or just done the preventative radiator swap.

Thanks in advance.
Nick
 

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I recall seeing some posts about A B or C shift solenoids and clogged screens. I can’t remember if that covers the issue you are experiencing. Hope you get it resolved since you put in some good effort to change things out after the pink milkshake.
I got “lucky” with my 2005’s radiator as it developed a small exterior coolant leak around 90k miles. That forced me into doing a radiator change that I was contemplating at 100k miles anyways.
Good luck with getting your issue resolved. Keep us posted if you figure out the solution.
 

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Discussion Starter · #3 ·
I've checked the C solenoid (front of trans just behind lower radiator), clean as a whistle. That is the only one I've checked, do you know if the others have screens or if coolant/water can somehow get stuck in there and cause the solenoid to fail? I'm assuming the shift issue was being muted a bit by the honda fluid (which I've read slows shifting a bit) and maybe a little gunk after 159k miles. Now the trans has been thoroughly flushed with Valvoline Maxlife.

Thanks
 

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Thanks for the write-up!


I would have probably skipped the SeaFoam. The reason is that it is thereby eliminated as a contributor to any future "issues", such as the one you are having. After having checked that things still run well, then I suppose you could have done a cleaning. Also, I'm not sure that waiting a day to do the rest of the job had a negative impact. How bad did the fluid look on the first drain?



In any case, if I understand correctly, not only do you not have Honda fluid in there now, you also have most of a bottle of SeaFoam, along with whatever contaminants it may have loosened up?
 

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Discussion Starter · #5 ·
On first flush it looked horrible, coolant on the bottom pink milkshake on top. Currently I have about half a bottle of sea foam trans cleaner in there which I did primarily because it said it gets rid of moisture. I have not gone back to DW-1, after 6 or 7 jugs of valvoline maxlife id like to assume that’s all that is in there.
 

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Could you disconnect the trans lines to the radiator. Then connect a large container of transfluid to the return line like a giant IV. Then run the other line to a catch pan and run until the fluid changes over while making sure you don't run dry?
 

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Can someone enlighten me on this radiator issue?? I'm smelling coolant faintly every time the pilot has been parked after a ride... sometimes during the ride(rarely). I have switched out the cap and that didn't work... I can't track down the leak but have been suspecting the radiator has a small crack and it's evaporating before I can see any leaks.

ANY and all info on this would be appreciated... It's been of concern and driving me crazy that I can't find it.
 

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If you open the radiator cap (only with engine cold) and/or look in the coolant reservoir and see a pink frothy milkshake your coolant and tranny fluid have mixed. This happens if the lower portion of the radiator where the tranny fluid goes into and comes out of fails internally.
If you’re getting a whiff of coolant take a flashlight and look over all coolant hoses, fittings, and both sides of the radiator for crusty chalky blue (assuming Honda Type 2 coolant) dried coolant. Mine had a very small leak behind the cooling fans. It never dripped onto the ground since there is a small lip where the metal radiator meets its plastic base.
Also look on the firewall where the coolant goes into the heater core.
 

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You can also perform a pressure test on the radiator to find the leak.
 

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Discussion Starter · #10 ·
Apparently the OEM Denso radiator is known to fail allowing coolant and transmission fluid to mix. most modern cars with automatic transmissions have dual purpose radiators most of the radiator has coolant, a very small area on the bottom provides temperature control for transmission fluid. These fluids are supposed to be kept separate, but when the divider between these fluids fails, coolant and trans fluid mix in the cooling system and the transmission. Not so back for the cooling system, but possibly catastrophic for the transmission. I'm at about 500 miles on my fix. still having issues between 2nd and 3rd on downshift. Front and left (passenger) motor mounts have about 60k on them, when I rev the engine I don't get any clunking, so those mounts are probably good. I might change out shift valve C, with my fingers crossed. I don't have any check engine or trans lights but the part is $50 so why not?
 

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Based on the limited sample size of data taken by one of the forum members the 2005 radiator appears to have the highest probability of a failure. As mentioned above Denso is the OEM supplier for the radiator. I did not hesitate to replace ours with another Denso when it developed an external leak. I figured I got a bad original unit built in the timeframe when Denso may have been experiencing some quality issues. If they hadn’t gotten their act together 10 years later I’m sure Honda would have found a different supplier by then.
 

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When I replaced the radiator last year. I went with Denso because I found out that Denso did update the rad some time down the road because of this failure issue.
 

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Can someone enlighten me on this radiator issue?? I'm smelling coolant faintly every time the pilot has been parked after a ride... sometimes during the ride(rarely). I have switched out the cap and that didn't work... I can't track down the leak but have been suspecting the radiator has a small crack and it's evaporating before I can see any leaks.

ANY and all info on this would be appreciated... It's been of concern and driving me crazy that I can't find it.
Do a search for "strawberry milkshake of death" and you'll find out more than you want to know. This is a faulty radiator design issue and affects other makes and models besides Honda/Acura. I hope the latest Denso radiator has corrected this issue. Reports over on the Ridgeline owners club appear to support the new design as correcting the issue.

I've taken the approach of replacing the radiator when I have the timing belt/water pump service done as a preventative measure. Time for a coolant change anyway.
 

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Discussion Starter · #14 ·
To update this. My transmission is still working fairly well since the radiator failure. Aside from some intermittent rough shifting from 3rd to 2nd, everything seems to be working okay after about 1500 miles on the repair, including a round trip from LA to SF. Fingers crossed.
 

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I just had the failure on my 2006 ridgeline. I believe the way it works is this:

There is an aluminum heat exchanger in the bottom plastic portion of the radiator. It is held in place by the aluminum nut that has male threads and an o-ring on the inside. It is held in place by sandwiching the plastic radiator housing (which is full of coolant).

The failure was the use of a ferrous washer that rusts and corrodes and expands, adding pressure to the male threads of the nut in the female threads of the heat exchanger for the trans fluid. Trans fluid is at a higher pressure than the coolant (I think), and when the nut pops out, first you will normally lose the trans fluid (either to the exterior or into the coolant, perhaps all dependent on the coolant pressure due to the temperature of the vehicle).

I think I got lucky with a failure on the trans fluid pressure side that comes from the trans to the radiator, and lost my trans fluid first. It is possible that suction at this fitting could suck coolant into the heat exchanger, or if a failure on the passenger side, you could suck coolant into the line that heads to the front of the vehicle for further ambient cooling of the trans fluid. Maybe you are more likely to have this issue if your failure is on the passenger side. I don’t know.

Anyway, the radiators apparently come pre-assembled with the connections torqued, and they should not be messed with. Note the markings on my new ridgeline radiator:





Sorry I didn’t picture my old radiator, but there’s info on the Ridgeline forum.



I am writing here to share some knowledge from ridgeline forum, and also verify that the issue also exists in my wife’s. I think it does based on these pictures I’ve taken:






Combine this issue with smell of coolant I’ve been getting from my wife’s 2007 Pilot EXL, and then this picture, I think I should change her radiator preventatively.



It looks like the radiator is definitely weeping a bit, and I don’t want to have my wife end up stranded.

I wish I’d replaced the metal trans cooler line that runs across the bottom of my ridgeline radiator, and also have extra 10 mm bolts ready, plus some plastic clips for the plastic parts. I hope to be more prepared for my wife’s Pilot repair.


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The photos you took of the rusted washers are very similar to posts I have seen on this forum for that same issue. I couldn’t tell if the crud on your wife’s Pilot radiator is crusty Honda Type 2 coolant (it looks green instead of blue on my phone) but if it matches the color of the existing coolant I’d say that radiator is living on borrowed time.

I’m like you in that I didn’t mess with the fittings when I replaced the radiator on my wife’s 2005. I wouldn’t have had a way to torque them to the proper value had I loosened them.
 

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I think I got lucky with my ridgeline.

Do you guys have any recommendations regarding the radiator brand?

The Ridgeline forum says TYC and Spectra are just as good as Denso. I’m getting ready to order and wonder if I should pay an extra $30 for Denso over Spectra, or if there are different issues altogether because it is a different radiator than the ridgeline.


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I don’t recall there being a significant difference in price for Spectra vs Denso, unless you buy Denso directly from your dealer.
Check out hondaautomotiveparts.com. That is where I order most of the parts for my wife’s Pilot.
I think Spectra was around $100 and Denso $140 a couple years ago for the 2005 radiator.
 

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I don’t recall there being a significant difference in price for Spectra vs Denso, unless you buy Denso directly from your dealer.

Check out hondaautomotiveparts.com. That is where I order most of the parts for my wife’s Pilot.

I think Spectra was around $100 and Denso $140 a couple years ago for the 2005 radiator.


Correct. The price difference is not significant. I was just wondering if anyone has had issues with either replacement.


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