Alright so I am completely stumped. This morning I was sitting in a parking lot waiting for my bus and my wife's 07 RDX started smoking. I looked down at my cluster and noticed the temp reading HOT so I quickly turned on the heat full blast and opened up the hood until it cooled down. I seriously cannot believe this car does not warn you when the car overheats, no lights or anything, is that normal?? I checked the coolant reservoir which was indeed reading "low" but I did not see any obvious leaks anywhere. I left the car in the lot until I got home from work. I popped off the radiator cap and there wasn't any coolant to the top of the radiator (I think there should be right?). I was able to make it home without overheating but it was definitely getting hot fast (I only live 1 mile from the bus stop).

Once I got it home I waited for about an hour and topped off the coolant reservoir with Honda OEM Antifreeze and tried to take it for another ride. About 5 minutes into the ride and I noticed the heat was rising fast again so I pulled it back into the driveway and checked both cooling fans which were running just fine.

Next I popped off the splash guard and did notice some coolant residue underneath the car but that was most likely from when it overheated the first time, I am assuming some coolant escaped when there was a lot of pressure.

I then drained all my coolant and removed the thermostat. I boiled a pot of water and let thermostat sit in the pot for about a minute and it fully opened, so again nothing wrong there.

Before I fill up the car with coolant again I want to make sure there is nothing that I am missing. Could it be the water pump causing the issue, how can I check that? It is a 2007 but I only have 80k miles right now. Anything else I can check or troubleshoot?

-Ben

 

Hopefully this is not the problem, but check the transmission fluid for signs of coolant in it & check the coolant for signs of transmission fluid in it.

 

the car did warn you! the temp gauge started rising!
every one of my past cars and future cars have this feature.

water pumps are made out of plastic, it may very well be a deformed water pump. check to see any leaks!

 

I'll check it.

Yeah not finding any leaks from the water pump area.

Yeah all cars have temp gauges I am aware of that but I figured I would get some kind of CEL or light when it actually overheats.

 

Where is the coolant going? Figure out that problem and you'll have your answer.

As suggested, the radiator sometimes fails and the coolant mixes with transmission fluid.

Good luck and keep us posted!

 

Not sure why there was low coolant but it seems like that was the issue. I performed a coolant flush and I fill the coolant all the way to the top of the radiator. So far I have driven 200 miles this weekend and the coolant level has not dropped at all. I also changed my transmission fluid and oil this weekend and there was no signs of coolant mixed in. I will have to keep an eye on it but hopefully this was nothing major.

 

Not to be a party pooper here, but the coolant had to go somewhere to get low in the first place. You must have a leak somewhere as it does not just evaporate. Keep checking that temperature gauge and coolant levels. The issue may rear its ugly head again. Hope I am wrong though.

 

Look at the exhaust manifold this is a often overlooked area. It has coolant that goes through it. Also it's a 10 year old car changing all the hoses at this point isn't a bad idea.

 

You say it cooled down when moving, but overheated when sitting. Are BOTH of your radiator cooling fans working?

If you're sitting with the car idling, it should be running both fans. 1st fan will stay on, 2nd fan will run intermittently as needed.

Might be a good idea to do a coolant flush as well, throw in a new thermostat just to be safe.

 

I have the same issue with my RDX and my mechanic told me to flush both but also replace the radiator. Not sure what to do at this point if it's worth spending the money or not??? What if it needs new transmission too? Can you give me some estimates if anyone else here did this before or had the same issue and how did they fix it? Thank you!!!

 

Hi and welcome to the board!

More details would help understanding your specific situation and condition at present time?

The radiator plugs for the transmission fluid corrode in time, due to multiple factors: different metals, exposure to elements, winter salt in the snow areas, acidity of coolant liquid over time, etc. Such failures affected other Honda/Acura models due to similar design.

There have been reports of saving the transmission even after catastrophic failure of the radiator and even full mix up of fluids while dumping them on the road at same time. One mitigating factor seems to be little to no driving at all until repairs done and fluids thoroughly flushed... as pressure of AT oil might be higher than coolant for just short while.

Not sure about the overheating consequence of such failure. There is one report of overheating and blown all engine gaskets, was the exhaust manifold not transmission related.
You may want to check, verify head gasket, especially cylinder compression values to ensure the engine is still operational (mechanic should know how) first, that is PRIOR to doing the rest of repairs, no need to run the engine at all.

In the case of the transmission it may need several times of simple drain, then refill, no flushing machine acceptable ( even shift few seconds through gears on the hoist to account for the liquid within the torque converter) until liquid comes out free of contamination. Repeat at least once more after a satisfactory test drive. Search for such threads on the rdx forum.

Radiator and coolant are cheap and have to be replaced too. Could do the belt and waterpump, thermostat at same time (100k miles belt service) if nearing such milestone TO save a little on labour.

CHECK OPERATION OF FANS, radiator cap, hoses, temp. sensors and all relevant relays, as some may have failed before this situation.

Hope it works out for you!

 

Thanks for the warm welcome and your detailed and helpful comment. I have been in the forum for almost 8 years lurking around but never had to post anything as I remember because my RDX has been in a pretty good shape until now. As you mentioned years go by and some big problems like this will show up eventually. After I checked it with my mechanic it's definitely an internal leak from the radiator to transmission and both coolant and transmission oil are mixed together forming a dark pinkish oil I would say. I will need a radiator replacement and a full transmission flush plus the thermostat. It looks like the head gaskets and all engine related parts are untouched and there are no leaks whatsoever. I didn't drive the car that much when I noticed the problem. It started to overheat as the temperature was raising and I believe I drove it for 10 min when it first started and then 10 more min to take it to the mechanic after a few days. Based on their estimate it will be around $500 to replace the radiator, thermostat and flushing including labor. I was told to get the tranny oil from the dealership for better performance. I spoke to them and they told me it will be around $300 for 12 quarts of oil which will be enough for 4 cycles of flushing. Can you please redirect me to a thread especially for this issue just to check how much is this if someone did it? I think it's a fair price for a grand total of $800 labor included. Dealership told me around $1100 and $1300 but my mechanic will save me around $300 to $500. Thanks for your help!

 

Figured as much. These repairs are then the cheapest attempt to keep the car going.

Here it goes:

rough budget if I was to do it all at once now ~ u$ 420 plus taxes:

1 Radiator 80
2g Coolant 50
Lower hose 40
Thermostat 40
Radiator Cap 15
Thermo sensor 10
3 gallons AT oil for cleaning/dumping 60
12L AT DW1 120
clear silicone for wet applications. 0
Large oil tray 5

I did the radiator replacement last year just to avoid such situation, just in time as rust was already building up in the pipe connectors, out of sight. The thermostat+cap was done the year before with the accessory belt work.

So from practical perspective it is EASILY doable, DIY, with under a few hours for the radiator.

Radiator, unbranded is under U$90 on eBay.

https://www.ebay.com/sch/i.html?_fro...diator&_sop=15

Premixed coolant, will need TWO gallons.
thermostat should not be too expensive, under 40 cdn$ from dealer maybe?
Radiator cap, may 25 cdn$

I used several gallons of DISTILLED WATER from Wal-Mart to do several flushes. In your case you have transmission oil contamination in the coolant circuit. You may want to do several water flushes, 1$ for each gallon of water to remove as much oil from the block as well.
** You may have to run the engine some 15 - 20 minutes to warm up without driving, radiator cap off, but allow 2-4hrs to cool off before draining and refilling again with cold water.
Once water is clear of oil, then you can remove the thermostat from the block, at the end of the TOP RADIATOR HOSE. That will drain most of the water, then refill with Honda coolant as last step for the radiator.
Watch for the radiator fan whether it activates or not, different issue related to relays in the electrical box.

Found the LOWER RADIATOR HOSE "quick release" impossible to remove on my 2008 with 230k km at the time. I disconnected it from the block and pulled the radiator with it.
Had to order a quick replacement from dealer, ouch, almost 100cdn$, had no choice but to wait overnight. Suggest replacing it at this time as you are doing the work anyway. If you order beforehand maybe half price compared to mine.

This is best time to do the thermal sensor replacement, before radiator goes in,

https://www.oemacuraparts.com/oem-pa...9tYXRpYw%3D%3D

maybe 10$ from eBay.

https://www.ebay.com/itm/37870-RTA-0...d/223466188197

Bead some silicone on the exposed brass & steel from the connectors and leave to dry the night before.

Here is the radiator DIY from this forum:

https://acurazine.com/forums/1g-rdx-...cement-951920/

I had a pair of ramps, 1 minute to have the front up, in your case may have to use jack, stands and wheel chocs, always safety first. In the discussion I noted that I did it WITHOUT removing the front bumper cover, just loosened the air dam underneath for access to tubes, wires.

Do the transmission DRAIN. To refill could use a few gallons of valvoline maxlife. After having the new radiator installed, you are going to drain it anyway several tines as being contaminated with coolant.

https://acurazine.com/forums/1g-rdx-...n-fill-794451/

Then use your AT oil of choice, 12L was only good for 3 time of drain and release in my case. As you know a single drain and refill only changes close to 50% of the oil. I did one at each oil change after I got the car used.
Even after three replacements I still had a palpable transition between gears around 60km/h, story for a different time.

https://acurazine.com/forums/1g-rdx-.../#post16408033

Good luck, post your outcome
Hth

 

For reference,from other previous threads, it is also recommended to replace the waterpump, all hoses and the expansion reservoir.

Message#11
Trent_ky story

Turbo area concerns
Message#17
Lakmus85

https://acurazine.com/forums/1g-rdx-...oolant-949321/

It is a secondary issue as it is part of the accessory belt system, work to be done ~ 100k miles intervals, extensive and not mentioned by those that checked your car.
Maybe it is not needed, so did not address it above either.

If the transmission appears to be behaving well, no turbo or exhaust manifold problems, certainly consider doing the water pump, s belt, pulleys, idler, tensioner, power steering related maintenance items, check A.C., in short order with the money saved by DIY the radiator and transmission instead of going to a garage/dealer.

 

Wow 😲 great conversation guys! I hope all goes well. Not sure I can add anything at the moment it sounds like all was talked about and covered already. I want to see photos and a write up if you do it yourself!

 

Errr... I don't like it but good thread at the same time.

I didn't know this was an issue with the RDX, but did know it was an issue for the Xterra because a friend had it happen. So I saw the transmission hookups on my radiator and have been thinking on a regular basis debating on just changing the radiator out or trying to read up on what to look for so I don't just jump into changing it out for no reason.

Mine is at 150K now.

I check the coolant and the transmission fluid every time I open the hood since I noticed the trans lines.

What specifically am I watching for at the connections? Minor rust? Major rust? Something else?

Is everyone just replacing the radiator with the same type and possibly at intervals based on salt exposure, etc... or are RDX folks doing a bypass like Xterra people are?

 

Here is a Honda Ridgeline discussion that has a lot more detail than any RDX thread I have read so far:

https://www.ridgelineownersclub.com/....53921/page-15

I chose to replace rad after reading similar reports regarding RDX. Cheap preventive maintenance or potentially terminal unexpected but likely failure, your choice might be different.

I did use smartphone and took closer inspection pictures of the steel washer, to see if it was relevant to my situation. Saw FAINT TRACES of rust showing up on its surface. More rust was present but just not visible from the awkward, in place, angle of examination.

Various reasons could eventually lead to this: salt, improper factory installation, electrolysis, coolant not replaced, overheating, excessive pressure from blown head gasket, etc.

Personally I think it is unavoidable due to stray voltage through the coolant over time. So I just did three drain and refill with distilled water, then replaced with fresh coolant again, just 11 months since last one also with fresh coolant. I will probably call it annual summer maintenance.

Bought a cheap unit from eBay for <100U$, then had dealer order the lower hose, it did not <want> to "quick release" after all.

Turns out it was a good call after all, found a radiator pinhole leak on its surface facing the A.C., no way could be found without at least pulling it.

Took advantage and bypassed the cooler/warmer portion. For the record I would NOT RECOMMEND the bypass on any RDX doing daily idling or numerous stop&go. The cooler transfers heat from transmission to the radiator coolant much easier during these conditions (think 100x easier as its liquid to liquid through the purpose built OEM internal part). For these situations the OEM might be a better choice due to its elaborate internal design of the INSIDE of the warmer/cooler.

For those with the bypass keep an eye on the temperature during idling, preferably with OBD2 application for exact temperature reading. In my case idling using distilled water the thermostat seemed to open just over 200F, and then later the temperature rise activated the radiator fan at 212-213F.
When exact temperature is not available, consider activating both fans via AC control-any time you expect be idling for a long time. In such cases 5 minute of combined idling, stop&go driving might be considered too long time.

I used transparent silicone and sealed-covered the washer. It probably won't matter in the end, but why not, given the easy access at the time.

With this setup I will just keep testing for stray voltage between radiator and battery at idling and off. When its high again will use distilled water for three flushes and coolant replacement. This is likely to be the last radiator needed on my car, 2008 base at 265k km.

HTH

 

The issue that blends transmission fluid with coolant is generally an internal radiator failure, and most likely caused by old coolant. If you stay on top of your coolant flushes, it's highly unlikely that this will happen. Coolant becomes corrosive over time as it breaks down, and age is a much larger factor than mileage in this case. Those running around with 10 year old coolant because their car is still low on miles are probably living on borrowed time when it comes to this issue happening.

 

Stray voltage through Rdx 2008 1 year old aftermarket radiator with less than 1 year old fresh coolant.
Certainly multifaceted. In my case 1 year old radiator with less than 1 year old coolant (refilled after 3 drain refill with distilled water), had already exhibited stray voltage of 0.2xx V with engine off. I just redid it and will retest in a few weeks time. What is your radiator stray voltage?

 

Take the cap off and put the test probe inside touching only the coolant.

Crank up and check again.

Then check voltage at the battery while running to see how the alternator and voltage regulator are doing.

 

Indeed, last year I tested like you said. I had practically nil voltage probing with just the fresh coolant vs the battery terminal, few weeks after installing the new radiator, engine off.

Obviously IF the coolant remained non-conductive after one year, even assuming a different, unidentified source of stray voltage from the engine, it would not be enabled and would not reach the radiator, probably not be a major concern to me. Hence my sharing the experience why after quick testing, I had to change a one year old fluid in a new aftermarket RDX radiator together with digital reading of temperature necessary to activate the radiator fan in my car.

During this past year my MID temperature display did go from seven to eight tiny bars, only twice - just a few seconds each time, and I am sure would not have seen it if I did not watch for it to prevent overheating.

After all I also

If anyone has a tester and the time to test and post results, would be great to compare the voltage between coolant and battery post, for engine off and idling cases. Without test results from other RDX owners, I can only consider my car "unique" - so far. I will be getting a new multimeter to do more testing.

Hth

 

Yeah try direct to the coolant. And maybe try a new meter.

I checked this with mine and it starts out appearing like it is reading but it quickly jumps to like 150 mV and keeps declining. I realized if I removed the probe from the coolant it was continuing the same pattern. No reading really.

Interestingly though, I got 0.597v going directly to the external part of the radiator core. 0.000v directly to the engine.

 

Thank you for your info.

Was it idling or off? How old is your coolant? Was the 0v engine reading to the negative battery post or to the radiator coolant?
Maybe the 0.597v was impacted by the paint layer of the radiator, though I would think it would reduce the value not increase it...

I don't mind spending $10 on a new meter to reconfirm reading. I do verify the meter leads crosstouching while on the smallest resistance scale, so feel my numbers are real in my case.

Testing to the outside of the cap allows more convenient expanded test timing, reading during or immediately after trips, think running pressurized conditions. I agree the actual number is somewhat inflated by the cap itself, even more so when cap really old, good only for a trend. Mine was new last year together with the radiator.

Ask and you shall receive, 146mV. Idling alternator voltage stable@14.3V.
Engine ground loop was replaced last year too, 6 gauge iirc, off the engine mount.

 

How often are you guys changing your engine coolant mileage/age whichever comes first?

 

I'm seeing splashing signs over the engine. Also should my Radiator be loose? I think I'm going to replace my radiator...

Thanks for any helpful information.

 

Welcome to the board! Tell us the story of your car if you have the time

Radiator should be somewhat loose in its supports, both bottom and top brackets, think a few millimeters.

You will need to find out then fix the cause for the splash, higher than normal temperature could be both the trigger and its consequence. Yes, radiator can be ONE of such causes, there are potentially many others!

Few questions to ponder before changing any parts:
Did you check the coolant level and colour in the radiator and nearby expansion container? When was it last changed?
How about the transmission oil level?
When did you last do the belt service and changed the water pump? Thermostat?
Are the fans turning on/off when idling, and when A.C. turned on? Both?
Is the cabin heater working hot when needed, constant or occasionally lukewarm, random?
What color are the splash signs when dried?
Does it match the coolant color, blueish for Honda's?
Did it overheat at all or for how long?
What did you do when it happened, kept driving, idled or turned engine off for awhile?
Any history of cooling or maintenance trouble?

Hth

 

Has anyone tried to ground the radiator directly? Wouldn't that work?