I've noticed today that my coolant is leaking and I have no idea where it is coming from. I've recently replaced the radiator cap so that can't be the cause. Should I replace the radiator or the expansion tank first? Any ideas? Car has 155k miles.

 

I'll take a stab at this!

Check first: wash all marks off, spraywash the radiator fins, let dry, is top hose cracked?

Test: idling from cold, do the fans activate with the A.C. turned on? Turn AC off.
Is coolant in the radiator showing apparent movement with the cap off? Replace cap.
Wait for just radiator fan to turn on, does it?
Use Torque app to monitor coolant temperature and find out if it ever warms up past 212F without fans turning on.
Drive for at least 30' and monitor coolant temperature to not surpass 212F. Any new leaks in the engine bay?

Based on pictures, there are coolant traces close to expansion tank but no splash marks like around the top hose, no leaks apparent off the tank cover. Some coolant seemed to have been spread around by the fans, quite a lot maybe.

If you are lucky, the new cap did trigger this: old cap was too old and was not holding pressure anymore, spilling into the exp.tank, whereas the new one kept the pressure and created a high pressure&splash leak off the radiator hose, air current spread it around. The hose (too old, crack?) or clamp (too old& weak) are much cheaper than new radiator. If you can confirm this, then most likely radiator is holding the higher pressure, most likely it does not leak.

Good news: expansion tank does not need replacement unless knicked or cracked by moving it around at times. Yes, it can overflow, if the cap is old or pressure reaches past the new cap pressure limit. Is that a new Honda/Acura cap or aftermarket?

If you are not lucky, there were moments the coolant temperature went past 212F to cause an unusual increase in pressure and blow off past the hose clamp, that you did not see, find the root cause...

I'm just a messenger, hth

 

Common failure point is the plastic/aluminum 'seams'


Just replace the radiator with a DENSO one (can be found on Amazon or rockauto.com)

 

My radiator was replaced as well due to a leak I did not even know about... they replaced it and I guess there is a piece that should come brand new with every aftermarket/oem radiator that is on the bottom of it where it connects to one of the hoses.
Since the ordered new radiator did NOT come with one, the mechanic took the old radiator one, placed it into new radiator and was like good to go... sure enough coolant was still leaking, so they had to order brand new radiator, and do it all from scratch but this time they made sure that little piece came with it...

My aftermarket radiator was around $200 and it came with the lifetime warranty... at the same time I had major work done, so my mechanic did not charge me for the install and a flush - just for the part...

Now, this may be completely different case with you in the case your leak is somewhere on the top of the radiator - not at the bottom...

 

Thank you, everyone, for the recommendations and feedback. I will try those recommended steps. Worst case scenario, I replace the radiator, since I do my own repairs it won't hurt the wallet too much. I plan on keeping this car until the wheels fall off so going to continue to replace parts as they break.

 

This

 

I ordered the Denso radiator on RA and lower tube on acuraoemparts along with other things like the thermostat. Might as well replace the thermostat while I have the radiator off. Will report back when I get around to it! Thank you everyone.

 

Thank you for followup, yes replacing the quick release hose might be a good thing for your plans.

Are you getting the temp sensor at bottom of radiator, a new one is less than 10$, 37870-RTA-005, coolant cost later is maybe more than that:

https://www.ebay.com/itm/2-Pin-Engin...sAAOSwY5ddSo7h

https://acurazine.com/forums/3g-tl-p...t-come-947383/

If you do go for the sensor as well, is there any chance you can verify the fan activation temperature via the OBD2, with the old one before and new one after?
Mine is likely original from 2008, it activates around 212F, turns off around 186F or below. I could not find any OEM specs for the part OR practical tests yet. The high seems to me too high for comfort, with zero practical margin of error in case of compression loss for any reason-like it happened to you. (I did not consider it when I changed my rad last year... this year new coolant did not make any difference afaik.)

Rad cap if too old or not enough spring tension?

Keep us updated

 

Great idea! I just ordered the sensor based on your recommendation. I will also check the temps for you when the parts arrive, both pre-install and post installation of sensor. You should replace the radiator cap because the center of the cap made of plastic erodes over time due to heat. Notice below on the right which is my old cap, the center has eroded compared to the new cap on the left.

 

for 2005 to 2008 Acura RL the sensor is actually different 37870-PNA-003.

 

sorry about the bad link, I stopped checking when it matched RL up to 2012, don't know why it doesn't work once pasted in.

Thanks for the rad cap image, that's what I was talking about.

Cheers

 

No worries! Also, the parts on Ebay may not be oem. No way it is thay cheap. I ended up buying two on acuraoemparts with acurazine promo code for 5% off. I don't mind the higher price since the car is paid off and I don't plan to ever sell it.

cheers

 

I see the two sensors you ordered, around water pump &thermostat housing:


The one sensor I was referring to is at bottom of denso radiator, numbered 22 on the diagram, part number not listed for 2008RL:

https://www.acurapartswarehouse.com/...tor-denso.html

It is shown on the same diagram, and this time listed as 37870-rta-005 water temperature sensor, which I believe just controls the rad fan and does not inform ecu of water temperature or displays its info on the dashboard indicator.

https://www.acurapartswarehouse.com/...0-rta-005.html

I remember there were some Honda engines with three sensors, then one was eliminated from the top. Is your current rad using one or just a dummy plug?

Btw, I did the warmer bypass at the same time, seemed to help the transmission temps a little, kept the transmission cooler in place, as is for the time being.

Hth

 

I have no idea but I have a 2008 so I'd assume it does not have the bottom sensor. Can anyone confirm this is the case for the 2005 to 2008 RLs?

 

Check your car DIY style: follow the radiator diagram, look at bottom of radiator for a 2 wire harness connecting to the radiator.
If there is one, its the sensor for the fan, none then dont worry about it.

Hth

 

I can confirm the temp sensors are not located at the bottom of the radiator for the 2008 Acura RL as today I replaced my radiator with a Denso one. I also replaced two temp sensors, thermostat, lower radiator hose and cleaned the EGR valve.

Took me 5 hours. A lot longer than I expected. The hardest part is getting the damn connectors from the bottom. Also hard was the bottom bolt of the thermostat cover.

I couldn't get my obd2 scanner to connect so I do not have the temp..but I bought a new one and will get the temp when the fan turns on in the next few days when my new obd2 wifi connector comes from Amazon. Thank you everyone.



temp sensor on the thermostat cover

temp sensor #2 near the EGR valve

 

 

Altair..i just did this for you. got my obd2 to work. my fans activated at 208 degrees with the new thermostat and temp sensors installed.

 

Wonderful, seems you have 4F margin of error before boiling out, in any case of loss of pressure. Keep it that way, you have a nice ride with a fresh new cooling system!

Mine at 212 is practically non-existant, so will watch it as a hawk!

Glad to see my info being useful!