8G: Engine Overheating during Idle because fan won't turn on (explained)

OP Notes: On my other job I repair HMNVEEs (Military "Hummers") and we usual go through this same problem mainly because the PCM relay box wears out. Because I starting to see many threads on this forum and many just scuff them off by saying "Hey go change the thermostat". This isn't a Nancy Drew mystery novel or some lost Ancient crystal skull alien bs. Most of them already changed their thermostat and the coolant flushed but still having this problem I felt obligated to make a thread out of this....


I'll use this as a questionare:

Quote:

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Originally Posted by Zero_4073

Hey guys. Haven't been on here in awhile. Anyway, my 8g 4cyl overheats while idling for a couple of minutes. If I'm in a drivethru, I have to turn on the heat and the temp goes down. Not too fun in the summer.

I've had this problem for years, and it's getting worse. I still had it after waterpump replacement, thermo replaced, and fluid flush.

Anyone else have this problem? Is there an Eclipse performance radiator that will fit?

Thanks

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Good question, now multiply that by 100 people and you get a serious problem. I went to a local Mitsu dealership and there were 7 Galants/Eclipse of the same gen sitting on standby getting this problem sorted out. I will bet clams even the dealership cannot figure out the problem (like they did with mine a few years ago). I can only imagine how many more cars are awaiting repairs or getting a 'for sale' sign because they couldn't solve it. And what's worse, isn't keeping your engine really hot for an extended period of time may lead to a blown head gasket?

The answer(s) are quite simple really.

If you have the Haynes Repair Manual with you (can purchase one at the local auto part store or online), flip through Chapter 3 on section 3-3: Thermostat, 3-4: Engine cooling fans ( Cooling, heating, and air conditioning systems) and Chapter 6 on 6-6: ECT & 6-19: PCM (emission and engine control system)

http://images.solidcactus.com/autobarn/hay68035.jpg

Because of copyright laws and whatnot, I cannot quote what's on this book but you might want to purchase one because it has really cool pictures in them (if you are into that sort of thing)

Basically, here are the components that are involved this overheating issue (in order):

1. Coolant System & Thermostat

2. Engine Coolant Temp Sensor (ECT Sensor)

3. Power Control Modual Box (PCM Box located behind glove box)

4. Fuse Relay (in fuse box)

5. Fan motor assembly

The majority here will see a problem with the idler fan not operating rather than the A/C fan kicking in so you you want to refer items 1, 2, 3.
Refer to items 4 & 5 if A/C comes on but the fan doesn't kick in.

I recommend getting a hold of this book, read it's contents, grab a friend, and work on this problem. According to my experience, the only real challenge is removing the thermostat and coolant (which are explained in the book) and the rest are unscrewing, unbolting, and unclipping stuff.

If anybody wants to add stuff like step by step procedures (in your own words) feel free to do so on this thread.

That`s definitely a lot of very helpful information, thanks a lot. I'm gonna save that just in case shit happens.

Have this problem right now my relay is junk in the fuse box. It is on factory back order, that was at my local napa, i have been waiting for 3 weeks now who know how long it could take it sucks

have someone here pull it out from a junkyard. just state what year and model your car is.

My car recently has been overheating and I have replaced the thermostat, radiator and flushed it. No leaks at all and the fans come on and it still seems to run at 3/4 hot. Could this be sensor related? Maybe it really isn't running that hot but the temp says so? What do you guys think?

If its a 4G64 , the freeze out plugs tend to rust out and piss out coolant. the rust corrodes everything includin your water pump. If its never been changed it may be a good idea....if your coolant is rust colored this may be the problem. Check underneath car for leakage every time you stop and shut it off. If there is a leak follow it to its location. Also make sure your exhaust is not smoking(head gasket)

alright pete is right i changed my ecu and they work

Thanks a lot for putting this together g-spot. I don't know how I never stumbled across this. So, from what you're saying, if I've replaced the coolant, thermostat, and fan, I have to change the ECM and ECM relay, which are these parts, that I've circled?

https://lh3.googleusercontent.com/-d...Y/s800/ecu.jpg

I do not have this problem per se but maybe I used to? Coolant would always drop but I figured it was leaking out of all steel non stock radiator so I I put a v6 radiator on my i4 and now my fan does not come on but my temp is always below normal not bya lot though, I have even driven it to Chicago. And during winter I could drive at highway speeds without the fan needing to come on I'm thinking because of larger flow volume. So I don't have this problem as my coolant levels have been steady 6 months.

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I have a 4cyl rad/fan assembly in my v6. full rad fluid, new water pump/timing belt. therm, and new temp sensor's. "both of them". i unplug the 2 prong one fans turn on/ check engine light as well. i plug it in. fans stay on until i turn car off. fans work but the computer doesnt seem to be turning the fans on. i thought i was the only one.

just bought a new ecu relay. Going to try that and see as the last straw. Gspot had mentioned that.

Just changed the ECU Relay and it didn't help.

So, now I have changed the following in order -

1. Thermostat
2. Engine Coolant sensor (one that controls the fan, not the gauge)
3. Fan Motor Assembly
4. The Fan relay in the fuse box
5. The ECU relay

Still no go. I guess the only thing to change that's left is the PCM. I do not have that kind of money to throw at my car, so I'm just going to live with it. I will change both the engine temp sensors (the one that controls the gauge and the one that controls the fan) again just to make sure. finald8ta in this thread pointed out there were two, so I'm going replacing both and seeing if it helps. So far my temp has not gone above 210, I don't know if that is normal, but I expect the fan to turn on about 200-203?

I had an over heating issue but it was because where the cam sensor goes there's two grounds and one was off once I put it back and was never any of the senors that I replaced

Was yours overheating to the point the gauge needle went into the red area? The problem being described here is only overheating while idling, but the temps never go into the red area (or the engine boiling).

Both