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Getting to the root of the overheating problem

 
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bureau13  



Joined: 07 Sep 2017
Posts: 211
Location: South Florida

PostPosted: Sun Apr 28, 2019 5:02 am    Post subject: Getting to the root of the overheating problem Reply with quote

So my overheating spawned a whole thread about whether the car was now dead or not (thankfully, it's not). I really need to address that overheating root cause next though. So...

It's fine at speed...stuck in traffic, in a drive-through, basically doing lots of idling...no good. This happens with the AC on or off. Definitely sounds like a problem with the fans, right? (Note...it wasn't doing this when I first got it).

At one point, months ago, I started having this type of problem, and I found that the fans were never kicking into high speed/AC fan was never coming on. Turned out to be a relay (cooling fan or AC I don't remember). I replaced it, then the fans started working as expected. Then I noticed problems again, and fishing around to see if the fans were rotating freely, I found a fan blade just laying in the shroud. Oops. I pulled the shroud, and the AC/aux fan had one blade on it. I replaced that. Well, I'm still having this same symptom. The main fan does run after I turn the car off if it's hot (for quite a while, too). With the AC on, or the car hot, both fans are running, and both are pulling air through the radiator (ie they're rotating the right direction). Putting my hand behind each, the main fan is pulling significantly more air than the AC/aux fan. Is this normal? I know the main fan is slightly bigger, but on high, I thought they were both rotating at the same speed. I guess they may be...I just wasn't expecting as big a difference in perceived air flow. Also, if I put my hand on the AC condensor, the driver's side (where the main fan is) is definitely cooler to touch than the passenger side.

Any thoughts on any of this? Sorry it's long and wordy but I wanted to capture all the observations. I have checked the obvious stuff. I don't think I've seen these symptoms and had it be something other than the fans, but I'm at a bit of a loss...
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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morghen  



Joined: 21 Jan 2005
Posts: 8131
Location: Romania

PostPosted: Sun Apr 28, 2019 6:45 am    Post subject: Reply with quote

You have to study the electrical diagrams for your specific model and year and understand how the fans work.
Then check what you have on the car and see if there is a problem in the electrical system or not.
My 931 had the wrong relay for one of the fans and no relay for the other.
This resulted in a weird overheating behaviour similar to yours.
Basically one cooling fan only worked on the first speed and the other didnt at all. Thats not the case here but still you need to look at the correct diagrams and check your car for bad repairs or damages.
Anyway..you may want to bleed the cooling system properly just to be sure.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1913
Location: Somerset, UK

PostPosted: Sun Apr 28, 2019 7:12 pm    Post subject: Reply with quote

Not only does the effectiveness of you electrical and fan system need checking, but also the quality of the coolant system which ultimately gets furred up over time reducing the ability to remove heat from the engine. Your radiator and fans need to be 100%, especially in Florida heat. Check every detail. Make it at least as good as new if not improve it. The turbo thermal management was always near its limit, more so in slow and stationary traffic. Maybe replace stock fans as rad for more modern and larger performance items..
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Then www.924board.org/viewtopic.php?t=31252
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bureau13  



Joined: 07 Sep 2017
Posts: 211
Location: South Florida

PostPosted: Mon Apr 29, 2019 12:57 am    Post subject: Reply with quote

I've gone through the schematics and other info that seem to match my car...there are a couple other areas I want to confirm (like that secondary fan speed issue) but in general, it seems to work as it should (with the exception of keeping the car cool, of course). I don't think it's even a Florida heat issue...we haven't got hot like we're going to.

What gets me is: This wasn't happening when I bought the car. Something has deteriorated since then.

One thing I changed early (and didn't immediately see any ill effects): I have the lower temp thermostat and fan temp switch.

In any case, If I keep driving, my temp needle stays barely off the low hash mark. I've taken that as a pretty good indication my cooling system (sans fans) is working well. But I can take another look.

I'm hesitant to go the upgraded radiator/fan route, because it worked fine before, so something is wrong, not just inadequate. Honestly, I'm suspicious of my aux fan. It's a used one, it does seem to work OK, but if I do have to replace it that right there might be a good argument for an upgraded fan system. I had a terrible time finding that thing...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1853
Location: MI

PostPosted: Mon Apr 29, 2019 1:51 am    Post subject: Reply with quote

I had my fans wired together straight from the alternator + through the fans, fans ground to temp switch on radiator, straight to chassis ground from the other side of the switch, so they both just come on full blast when the switch closes. Worked good..
But now I just put them on my MegaSquirt and have them set based on my coolant temp at the back of the head.. Works better..

I think the stock fans and radiator are adequate components.

No bubbles in your coolant expansion tank with the cap off?
Are your radiator hoses getting hard with pressure when up to temp?
Do they stay pressurized for a while if you shut the car off hot?
Can you feel your radiator for hot spots/cold spots indicating blockages?

If all that is good I would be checking on your water pump.. Maybe it isn't performing well at low RPM if their is something wrong with the impeller decreasing it's pumping efficiency..
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bureau13  



Joined: 07 Sep 2017
Posts: 211
Location: South Florida

PostPosted: Mon Apr 29, 2019 2:30 am    Post subject: Reply with quote

Thanks for all the input, guys. I am pretty sure I found the problem: Me, and making stupid assumptions without REALLY checking things. My secondary fan was wired backwards Since it was used, the keyed part of the connector was broken, and it can fit on either way. I "tested" it by sticking my hand behind it when it was running, and sure enough, I "felt air." But remember how it seemed weak? That's because it wasn't actually blowing on my hand, it was just disturbed air that you feel behind a fan. I tested it properly with a piece of paper on the front of the condenser, and sure enough, on that side where the secondary fan is, the paper blew away, rather than got sucked to, the condenser. STUPID! I switched the wiring...haven't tested it other than the paper test yet, but I'm sure that's it. Maybe I'll go "test" it at Arby's drive-thru

Feeling pretty stupid...
_________________
-----------------------------------------
1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1853
Location: MI

PostPosted: Mon Apr 29, 2019 2:34 am    Post subject: Reply with quote

Naw, stuff happens, lucky find!
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