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Hello everyone,

I've new to the forums! I've been working on a 2004 honda accord 2.4L DOHC v4 for a couple of days now doing all of the routine maintenence and this one has stumped me....

The symptoms include:

  • engine overheating (80% - max) on temperature gauge
  • top radiator hose hot
  • lower radiator hose warm
  • radiator fan not turning on (only turns on when A/C is on) also jump started fan. and it works
things I've checked include:
  • lower driverside temperature (ECT) sensor. looks good. no green cust or anything.
  • new thermostat + housing. Also tried removing thermostat for bypass.
  • new OEM coolant.
  • no CEL
  • jump started radiator fan to see if it was operational. It is. (fan does not turn on automatically when engine overheats though)
  • A/C is cold and works
  • no white smoke.
  • Checked relays. Switched it with block heater relay
I have not purged air from the system yet, as I don't know how to on a 2004 honda accord. (wondering if someone can direct me to something on the forums). It would be greatly appreciated if someone could help me out here

Background:

just purchased the car, did all of the checks, engine temp was fine during and a day after buying the car. Added coolant to system. and BAM. this happens.
Thanks!
 

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Discussion Starter #3
Did you check the relay?
I apologize, yes. I switched the relays with the engine block heater relay. Could air pockets cause this issue? how do I purge air from the system? I would assume there's a humungous air pocket from the lower hose when I reconnected it
 

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Saw it as well, but it's ok.
OP, I haven't bled air from cooling system, so I don't want to advice you based on my internet education. Hopefully someone will chime in sooner rather than later, but you should really search for it since it has been covered many times.

Before you attempt anything though, remember not to open the radiator cap with the engine warm.

Along with the info that you will find at this forum by searching, you can look at eric the car guy's videos/page for this just to get an idea.

Enjoy your I4 :wink
 

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You can quicken the burping of the coolant if you drive the car up some ramps to get the radiator filler neck higher than the engine.

Open the radiator cap WHEN THE ENGINE IS COOL and remove.

Start the engine and run it until the radiator fan starts.

You'll see the coolant burping at the filler neck and the level may even drop.

Keep adding coolant to the filler neck as that level goes down.

The problem you may have is your fan doesn't run but you will see the burping stop when the air is gone.
 

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im a tech so my advice may not help you, cause i can only tell you what i would do with my shop full of tools.

first i would check for DTC's. Just cause you dont have a MIL it doesnt mean that you dont have DTC's. i would monitor the ECT sensors 1 and 2 before start up and while running. Im guessing your ECT 2 is working becuase you can watch the guage move normally despite the higher temps. These cooling fans typically operate around 180 degrees. Mine turns on at 176. if they didnt come on once ECT 1 reached above that temp i would check to see if the ECM was commanding the fan on. If it was, then i would check the relay circuit.

The relay has two sides of a circuit. the "control" side and the "controlled" side. the control side has a constant positive feed while the engine is running and the ground is controlled by the ECM. Once the ECM energizes the relay, the "controlled" side is connected allowing power to flow through it.

I would review the schematic, and check to see when power is supposed to be available at the "controlled" side, and make sure its there. If its not, then i would review the power distribution schematics. If it is, and the relay is good (which you say it is) then i would check for power at the fan.

Another quick check you can do if you have a schematic is checking the fan grounds. engine running, off, key on, whatever you will still have a ground on one side of the fan connectors. If i remember right.

Its hard to offer advice without the schematics in front of me. the fact is, there are numerous different scenarios/reasons why a single part wouldnt operate. If it was easy, i wouldnt have a job. LOL. If you want, i can print the schematics and trouble shooting procedures out for you and fax them. let me know. If i have a minute at work tomorrow i would be happy to help.
 
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Test the ECT switch by unplugging the connector and make a jumper with a paper clip. Your ECT switch could be bad.
 

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the control side has a constant positive feed while the engine is running and the ground is controlled by the ECM.
Ugh, switched grounds are against my religion. But you see them occasionally. Any notion as to why the circuit would be controlled this way?
 

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Ugh, switched grounds are against my religion. But you see them occasionally. Any notion as to why the circuit would be controlled this way?
Iv never thought about why. Its just how most ECU's work. typically the ignition switch powers up the majority of the vehicles systems, and multiple ECU's turn components on via the ground side of the relay. Iv worked for Honda and GM. both operate just about the same way.

Dont be discouraged. Electricity works the same way regardless of how you switch it. :smile

If you need schematics let me know.
 

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Drain out a little of the coolant and look at the inside of the radiator. Is it full of gunk, or are the passages clean? If not, you may be dealing with a clogged radiator core. You can try draining the system and running some Prestone radiator flush along with water (tap water is okay for this) for a few hours. Flush it all out with distilled water, then add coolant (or new coolant). If that doesn't work, you may need a radiator.
 

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Dont be discouraged. Electricity works the same way regardless of how you switch it.
Oh, I know. But I like ground to be a nice, fixed reference everywhere. There must be a reason wherever it's done differently, and I know nothing about automotive systems.
 

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Admittedly low tech, but I found that squeezing and letting go of the lower and upper radiator hoses repeatedly would force the air pockets to the top (engine off and cool, radiator cap off)

There is a small chance that the water pump impeller broke and there is no circulation of the coolant. That happened on my first car, (I probably poured coolant into a nearly overheated engine which is a big no no),.
 

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I would definitely bleed the system, remove radiator cap when car is cold, start the car with heater all the way to hot and fan operating full blast, and raise rpm to 1500-2000rpm and squeeze the hoses to allow air to flow through. You should actually see the bubbles coming out, keep doing this until no more bubbles come out.

Also is the car over heating during slow city speeds or is it on the highway or both? If its only in city speeds it could be a fan issue and on the highway it would be radiator fins or some debris blocking the flow of air.

I would definitely check the wiring for the fans and relays since they don't come on unless is AC is on.

Good luck.
 
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