2008 g35 overheating.

Fans run, but appear to only run on low.

Are there 2 speeds?

I replaced the module a few months back. Could it have gone bad again?

Are there perhaps relays?

Thanks

Should be relays for the fans, yes.

I'm fairly certain they're a 2-speed design but I don't know if it's ECU-controlled or if they simply kick up when AC is turned on (easy to check).

Is the rest of the cooling system in good repair? Lots of factors can contribute to overheating.

I think everything else is good. Last time it overheated, I added more coolant, so it's full and burped it by using one of those funnels that lets you burp the system.

I just let it cool down fully, and restarted it. It's 110*F here today, and the fans are not coming on with it just idling in garage. I checked the temperature of the top radiator hose and bottom hose, and they are 199* and 193*.

If I turn on the A/C, the fans turn on to what appears to me to be "low". I can barely feel the fan doing it's thing, but both fans are turning. The radiator fans will "idle up" faster so I can feel the air blowing by the fans much harder for about 3 seconds and then it goes back to normal (barely feel the air) and just keeps cycling low.. then high for 3 seconds, then low again.

I turn the A/C off, and both fans turn off.

I am a bit puzzled

So, an update:

I drove the car around for a good 20 minutes (NO AC running), and the temperature according to Torque, got up to 212*.
- I stopped and looked at both fans, and they were both running on low. I never found them on "high".
- They never attempted to go to "high"
- I got home and turned on the AC, and I could hear the fans start to blow harder but then go back to low. It did this constantly.
- The car temp went up to 221*, so I turned it off.

Background:
I had a problem late last year where the car never got to temperature, so I got a code (forget which one), and it appeared the fans were running non-stop on high, and the car could not get to full temp.
- I replaced the Fan Control Module with a new one, and the car then got to the 185* mark, and the fans stopped running on high.

Still stumped, but 2 thoughts:
1. The Fan Control Module has gone bad?
2. The fans themselves are bad and just can't spin up (not sure why they'd slow down)?

I'd lean towards the module. Fans are a simple machine, and rely on voltage input to go from low to high speed. Hard to imagine them both failing. Here's how to test it: https://www.youtube.com/watch?v=u0-kgf9fjeg

Don't cheap out and run a Chinese knockoff. The control module is a common failure item on that car. Here's a source: https://www.z1motorsports.com/cooling/n ... 10493.html

However, your issue late last year doesn't make sense. You could have both fans running at twice their highest setting in freezing weather and the car should still reach operating temperature. That's the thermostat's function.

I'd pressure test the cooling system, replace the fan module, check all your grounds and fuses, replace the thermostat, and then flush the coolant (replace with 2 quarts of straight coolant, 2 bottles of WaterWetter, and the rest should be distilled water).

Letting it get over 190* (for 'testing') isn't a great idea.

I dont have the computer program the guy has in the video, lol. Wish I did.

I know replacing the module last year solved the problem, so I didnt replace the thermostat and housing.

Odd that the fan module would fail again, but its possible.

Thanks for the reply and opinion. Going to get a new module and thermostat.

What does pressure testing do for my issue? I dont have any leaks.

There's always a possibility of leaks. 200* coolant can evaporate before making a puddle, so a leak may not be apparent.

Also, old radiators have a way of cracking in an airspace (like near the top), so it compromises the pressure-holding capability of the system, but doesn't allow leakage.

Thanks for the explanation on the radiator testing.

Update:
I got a new control fan module, and before I installed it, I disconnected the old one and applied 12V directly to each radiator fan, and they turned and blew strong, getting a full 12V.

I installed the new fan control module:

I turned the car on with AC off, and the radiator fans did not turn on. I turned on the AC and the fans turned on both running slow (not high speed). I turned the AC back off, and the fans turned off.

I let the car heat up to 200* (according to torque/OBDC), the car gauge still shows in the middle, and the fans would not turn on without the AC on. With the fans on, they ran "low". I turned the AC off, and the fans stopped.

I am going to go ahead and replace the thermostat housing this weekend.

Could the temperature sensor be bad?

Absolutely. If it's reading wrong, that'd cause havoc across the board.

So, I removed and tested the thermostat, and it wasn't opening all the way, so I bought a replacement.

While tightening down the bolts for the thermostat housing, using a torque wrench, set to 89ft/lb and I twisted a head off one of the bolts.

What are the odds that this thing will hold with just 2 bolts? <0%?

Getting a drill bit centered and a screw extractor into the tight area, where I have zero visibility is going to be close to impossible.

I am getting too old for this....

WHOA. Hold up. 89 ft/lbs? Nope. Maybe 89 in/lbs. Your wheel lugs don't even need 89 ft/lbs.

Might be time to hand this one off to a mechanic. You were doing awesome up until that part!

In lbs....

That's about 7 ft/lbs, so I'm gonna guess there was some good corrosion on those 10mm bolts.

Ugh. Well, a drill and an extractor is your best bet now. Make sure you have a good tap to clean the hole (should be 6 x 1.0).

Just got this idea.

Remove the housing, which will leave some of the bolt exposed. If enough thread, add red threadlock and nut on it and try and remove it with socket.

With the housing removed, there should be little to no tension on the bolt thread.

Oh, hell. Yep. In fact, you should be able to grab it with a vice grip. Skip the threadlock, it's anaerobic and won't do what you're thinking it will.

Took the housing off, and then I was unable to get the broken bolt and take it out - easy breezy.

So, it's all put back together, and the problem hasn't changed any. Burped it using one of those funnel things as my G doesn't have a burp plug in the back.

Low speed fan comes on at about 206* with the AC off. I turned the AC on, and low and behold the fans turned on high!

Take it for a test drive, and it heats up to 219*, with the AC on. I pull over to the side of the road, and the fans are low, I hear that the fans are running low, and trying to spin up fast.. I can hear the fans RPM increasing, then dropping back down, never getting to high-speed and it repeats the cycle constantly. It knows it needs to speed up the fans, but it just isn't doing it.

I already replaced the control fan module - twice, once in March, and just now. I previously tested the fans directly with 12V, and they both spinned up on high with no problem.

If the sensor is reading temps out at 180, 200, 210, 219, I don't think it would be the temperature sensor.

Bad fans?

Just to close this out, I replaced the radiator fans today and its keeping cool.

I could immediately tell the fans were stronger than the old ones, and they were on immediately.

The fans came with a new control module too.

Max temp 205* with ac running and sitting at a light in 110* weather.

Thanks for all the help.

That's an odd one. Did you swap out the module or just the fans?

Nice work!

AZhitman wrote: ↑

Wed Jul 22, 2020 8:38 pm

That's an odd one. Did you swap out the module or just the fans?

Nice work!

I first replaced the fan control module to see if it had an impact, and it didn't.
I then replaced the thermostat/housing to see if it had an impact, and it didn't.
I then replaced the 2 fan assembly (which also came with a new module), and it had an impact, as the car is no longer overheating.