apocalyptic.angell

I have a 99 tl with about 186k miles on it. It was running well until recently it started "overheating". The temp gauge on the dash normally would stay a few ticks below halfway, but it recently when I turn the car on in the morning, the temp gauge starts about 2~3 ticks below halfway and rises from there to about the 3/4s point of the gauge. I started by doing a coolant change, then replaced the thermostat, and then the 3 temperature sensors close to the thermostat housing and still no change. After that, I borrowed a friend's ODB2 scanner and monitored temps as I drove around a bit. Using that, I can see that my coolant temps are about 170-180 (Thermostat temp, normal?) doing 65 on the freeway, but my gauge needle indicates that I'm am getting close about 3/4's of the way to overheating. Any idea what would throw the gauge off? Bad ground? Gauge damaged?

Also, related, about the same time this started happening, the radiator fan stopped turning on when I turned the car off. I know the fan still works, the fuses and relays work, I just replaced the switch (see above). I don't know what else would control that. I do know though that when I turn the AC on the fan come on.

Any help on either would be greatly appreciated, and yes I have searched the forums, but I couldn't seem to find anyone with these symptoms, but maybe I'm a poor searcher.

01tl4tl

you replaced the correct fan temp sensor A, on 99 its at thermostat
did you BURP the cooling system? per book
heater on full hot and fan on

driver fan runs with temp increase at stoplights, and with ac on, and 1-2 minutes after shutdown at normal temp
is that working right?
may be actual fan failing

apocalyptic.angell

Yes, I replaced fan temp switch A, the gauge temp sender, and the ecu temp sensor.( Part #s 37760-P00-003, 37870-PK2-005, and 37750-PH2-014 respectively) As for burping, I did my best to follow the instructions in the book : 30s with rad cap off, fill, 1500 rpm with rad cap half on till fan turns on twice, fill, 1500 rpm with rad cap half on till fan turns on twice, fill if needed.
however, when I was trying to burp it, I didn't know that my dash temp gauge was wrong so I ran it till it got almost to the red line on the temp gauge, then shut it off cause I was afraid to overheat my engine. After hooking up to the ODB2 and reading the actual coolant temps in the ECU (and double checking with an infrared thermometer) I know that I probably only ran it until it got to about 190~195 which isn't hot enough for fan temp switch A to kick on (needs to be ~200, or ~220 for fan switch B). So I suppose I could redo the burp procedure which might help, except that fan temp switch A doesn't seem to be turning on the fan.

Right now my driver's side fan only runs either when I turn on the AC or if the engine gets to ~220 and fan temp switch B kicks on both fans. It doesn't turn on at ~200 (when temp switch A closes) nor does it run at all after shut down.

As a side note, I just found the pdf of the OEM service manual so I'm going through that as well, although there is no troubleshooting case that matches mine.

Thanks for your help 01tl4tl. I see you on a lot of threads so I'm sure you must spend quite a bit of time on here helping others.

01tl4tl

temp guage ground?

the driver fan needs to run when at idle at stop lights,,on for 15-30 seconds then off
it should also kick on shortly after engine off as temp increases from no coolant flow

one thing- on burping= the heater must be turned on full hot,,cabin fan on,
open the doors to let air out
that mini radiator hides coolant and air

I used to be here lot more,,now I have somewhat of a life--a 2 wheel honda~
still like to work on the strange probs

apocalyptic.angell

Well, I swapped out fan temp switch A again (took the "new" one back to AZ for a warranty replacement since it didn't seem to be working like it should) and it seems the fan now turns closer to the temp I'd expect. (~200 F) I think this switch is actually closing closer to 205. Also figured out that on a 99 both fan always come on together, cause the ground pins on the relays are tied together. Also according to the wiring diagram, the fan switch B does nothing to actually turn the fans on. All it does is feed into the fan control module to tell it the engine is hotter than normal and to run for a while.

So I believe that my fans are now turning on when they should except for right after I shut down the car which can only mean that the Fan Control Module is damaged.

As for the temp gauge, the ground checks out as just fine. And if I disconnect the wire from the temperature sender/sensor the gauge drown past the cold as if the car was off so there is no odd voltage. That leaves either the wire (though it's hard to imagine the wire suddenly changing resistance) or the sensor itself which I'll check this afternoon. Spec says it should have a resistance of ~137 ohms at 133F and a resistance of 46 - 30 ohms in the 185 - 212F range.

Hmmm... I'm wondering if maybe I should avoid AZ sensors in the future...

01tl4tl

try oreilly for electrical or acura
zone is for cheap replacement parts,,not always above oe qualit

shared grounds are common--thats not what operates the fan

what does owner book say on fans? www.owners.acura.com
if you dont have one its free download there
its not realistic to think both run all the time,,temp would be way too cool and engine wont run correctly

wires to sensors not swapped?
burped system after sensor left system open during change?

apocalyptic.angell

I guess I should have clarified my statement about the grounds being tied together. The ground pins of the condenser fan relay and the radiator fan relay are tied together before going to radiator fan switch A which is then tied to chassis ground. So when Radiator Fan switch A closes, both fan relays close and hence both fans always run together as shown in the schematic below.



Yes, I did the full burp procedure thursday night right after I put the exchanged temp sensor A in. Actually knowing what spot on my gauge corresponded to what coolant temperature I wasn't afraid to run slightly above the "overheat" line to get the fans to turn on.

I think it'd be pretty hard to swap wires since all the connectors are different, and too short to reach anywhere else unless I misunderstood your meaning.


On my drive into work this morning though I was listening and the fans now kick on at stop lights. Not every stoplight, but enough that I'm comfortable they are running how they are supposed to. But the fans still don't turn on for the normal 1-2mins after shutdown which by looking at the schematic and process of elimination the only thing that can be is the fan control module. Luckily the OEM replacement is only ~$30.

Also the temperature gauge itself still isn't reading correctly. I checked all the appropriate grounds and they are all tight and connected. I'm still working on checking the gauge temperature sensor. I do think it is slightly our of spec, but if it is its about 10 ohms too high which to the gauge should look cooler not hotter.