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Discussion Starter #1
I have a Honda Odyssey 2012 EX-L, and it has 132K miles. I have an overheating issue for a long time, and I could not figure it out the real cause of the issue. The overheating only happen when the following things happen at the same time:
  • Outside temperature reaches 100+ degree.
  • Climbing uphill in a low speed (20 to 30 mph)
  • AC is ON.
All other time works fine. FYI: I have already replaced the following:
  • Thermostats
  • Radiator Cap and all FAN relays
  • Radiator
I see no sign of leaks, and the radiator has max of coolant. Both fans also turn on fine when I start the car. I suspect that the fan did not turn on max power to cool down the engine as there is not enough airflow during climbing at the low speed. Any thoughts on this? Also, I am trying to replace both ECT sensors (ETC Sensor #1 and #2(Fan Swtich)), but I am having trouble to locate the ECT sensor #2 (Fan Switch). Can anyone help me to locate where is ECT sensor #2?

Any help is appreciated. Thank you.
 

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I have a Honda Odyssey 2012 EX-L, and it has 132K miles. I have an overheating issue for a long time, and I could not figure it out the real cause of the issue. The overheating only happen when the following things happen at the same time:
  • Outside temperature reaches 100+ degree.
  • Climbing uphill in a low speed (20 to 30 mph)
  • AC is ON.
All other time works fine. FYI: I have already replaced the following:
  • Thermostats
  • Radiator Cap and all FAN relays
  • Radiator
I see no sign of leaks, and the radiator has max of coolant. Both fans also turn on fine when I start the car. I suspect that the fan did not turn on max power to cool down the engine as there is not enough airflow during climbing at the low speed. Any thoughts on this? Also, I am trying to replace both ECT sensors (ETC Sensor #1 and #2(Fan Swtich)), but I am having trouble to locate the ECT sensor #2 (Fan Switch). Can anyone help me to locate where is ECT sensor #2?

Any help is appreciated. Thank you.
its possible your radiator efficiency has been affected somehow.
is the AC condenser in the lower front free of debris/damage?

was there any work done on the van in recent years, where the coolant was changed out?
was distilled water and coolant or premix used?

grab the manual from here, and do a find for "ECT Sensor" you should be able to find what you're looking for.
 

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Discussion Starter #4
also, is the VCM muzzled on that?
Hi Ticket, Thank you for your response. I found no debris/damage on AC Condenser, and the coolant was changed last summer (05/2019) by a mechanic, and I am pretty sure that he used a coolant (no mix). I do not have VCM muzzled.

As I googled, I learn that ETC sensor controls when the FAN will be turned on HIGH speed. As I mentioned, the overheating issue only happens when the weather is hot (100+ degree) and driving at low (20 to 30 mph) speed uphill (8+ degree incline) with AC is ON. Do you think ETC senor will fix the problem? Thank you.
 

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2012 EX-L, >117k miles, VCM Tuner, Honda tow pkg.
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I'm sure the mechanic used compatible coolant but it would be worth checking it. A cheap coolant tester is available for a few $ at parts stores or walmart.

Also what color is the coolant? It should be blue if Honda brand or one of the knock offs. Or yellow if it is a universal coolant.
 

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2007 Odyssey EX-L
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+1 on checking the color of the coolant. Honda coolant or compatible coolant is supposed to be blue. There is a small chance that it could be red (I think Zerex Asian formula comes in blue or red dye but it is the same formula).

If different coolants were mixed, the color might be something funky like brown (like the coolant in my Toyota Camry that I bought used).

Was this problem occurring prior to you replacing the thermostat? What brand thermostat and radiator did you use?
 
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I'm sure the mechanic used compatible coolant but it would be worth checking it. A cheap coolant tester is available for a few $ at parts stores or walmart.

Also what color is the coolant? It should be blue if Honda brand or one of the knock offs. Or yellow if it is a universal coolant.
pentofrost or honda blue only...

I wonder if the tech used tap water, the minerals in the water used to cause issues with the rad.
maybe its not an issue anymore with aluminum rads, but I have seen the damage using non distilled water on copper rads.
could be a misnomer...

as rmyoder mentioned, test that coolant...
 

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I just remembered. My uncle had an 03 MDX with about 170K. He bought a boat and would tow the boat with the MDX after adding a transmission cooler. Around the same time he bought the boat, his radiator started leaking so he had that replaced. For some reason, the temperature gauge would climb when he was climbing hills with the boat. Obviously there was an additional load, but the boat was within Honda's towing specs. He made sure to never overheat the car and the car drove perfectly fine. He ended up selling the MDX at 176K and bought a Pilot so we never figured that out. I suspected that either the aftermarket radiator had a different design that restricted airflow, or the external transmission cooler that he added on blocked the radiator enough so that there was insufficient airflow.
 
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