alltrull

2008 TL-S 5AT 75k miles, 3rd owner 3 great years, (Houston, Atlanta, now Mobile, AL). Garaged, well cared for, do most of the maintenance myself. Radiator fans work for the A/C but not for engine overheating.

Hello all, long time lurker who wants to thank all of you who have helped out many of us without the proper acknowledgement.

Friday July 1 evening I noticed the engine stayed HOT for 2.5 hours after shutting it off in my garage. I know we are in the middle of summer but this was unusually hot. Minor coolant on the floor from reserve tank burping. I had topped off the reserve tank with distilled water & replaced the cracked reserve tank cap the previous weekend while doing routine maintenance.

Saturday morning I trouble shoot the fans work when the a/c is on. I swapped the a/c relay with the radiator fan relay. Fans worked again for the a/c but not for engine heat, no change. Located the thermal sensor at the thermostat, disconnect the thermal sensor plug, no change. Shorted out the female plug (wiring harness), radiator fans kick on. GREAT, found my problem.-

Being a proactive procrastinator, I ordered OEM parts (thermal sensor, upper & lower radiator hoses, 3 heater core hoses, thermostat, radiator cap, 2 gallons Honda Type 2 coolant, & a serpentine belt).

Last night & today I completed the parts & coolant change. Even drained the engine block (thanks again to all who contribute to this great forum). Yet I still have the same issue, no radiator fans when engine gets hot. I even reset the ECU, no change.

Sunday night 7pm, I’m done for this weekend, I have to shower, eat & prep for the work week. Thank goodness for a second vehicle. Contacted a coworker who is going to bring in his scanner to let me borrow (maybe I should have started with a code scanner first, live & learn). While I was in the shower thinking about the shituation, I wondered if there might be a second thermal sensor. After eating dinner (chicken gumbo & adult beverages) I checked and there is a second thermal sensor at the bottom of the radiator.

Could this radiator thermal sensor be my real problem?
How can I diagnose the thermal sensor resistance &/or voltage to the thermal sensors?
Code scanner first to see what the codes can tell me.
What am I missing? Searches on the forum have not revealed anything like this.
Any troubleshooting skills, flowcharts, or tips will be highly appreciated.
BTW, I will not be able to check the forum and respond back until Monday evening when I get home from work.

Thanks for all you do.

alltrull

Edit: Dash temp gauge is not showing the over temp condition.

rockstar143

iTrader: (6)

The funny thing is that you already seem like you're better at diagnosing problems than about 98% of the people on Acurazine.
I am limited in my knowledge...immediate thought was relay, but you addressed that...no fuses either, right?

My e-tuner said he bumped my fans to come on 10C lower temp...which tells me that it's a controllable thing.
I'm really unsure what to tell you but I'll follow along to learn stuff too!

tk2k6

Is it possible that you overlooked something while purging the air out of the cooling system? With air trapped in the cooling system all cooling sensors located at the top of the engine will be erratic just as you described it. The coolant temp sensor can't take a proper reading if there's air trapped in there. There could be something wrong with the heat control valve. This part needs to be open while bleeding the air out.

alltrull

Hi all, thanks for the input & feedback.

I did have the water valve open to the heater core while the vehicle was running. Plenty of heat in the cabin (and in the garage and outside), so coolant was definitely flowing through the heater core. My entire coolant system consumed 1.75 gallons of coolant, so I believe there are no air pockets to be bled. I have also searched for any procedures for bleeding air out of the coolant, none were found. The only thing I found was to have the water valve open to the heater core, check.

I paid the high retail price $45 at my local Honda stealership for thermal sensor p/n 37870-RTA-005 today. My coworker brought in his code scanner for me to borrow (gotta get one, hint). I worked 3 hours of overtime time tonight before I could come home to this project.

I had several codes, only P2185 & P0118 were coolant related.
P2185 Engine Coolant Temp Sensor 2 Circuit High
P0118 Engine Coolant Temp Circuit High Input

I drained the radiator into a clean kiddy pool, changed out the thermal sensor (bottom of the radiator next to the lower radiator hose), refilled the coolant, started car, no leaks, the code scanner also let me monitor the engine temperature at approx. 200 degrees, the radiator fans came on. SUCCESS !
I cleaned all the codes out and reset the ECU. Wednesday night I hope to flush out my brake fluid and replace with MOTUL 5.1

Thanks again to all that post their tragedies & triumphs.

Bottom Line: we have two identical thermal sensors 37870-RTA-005 (one at the thermostat and the other at the bottom of the radiator next to the lower radiator hose), replace them both.