Engine cooling fan modification and wiring diagram.

[BigLee]

This modification will allow low speed fan operation at a lower than stock temperature,
without setting any codes.

This is a 3-speed fan, with two resistors built into the fan motor itself, to limit motor current on the two lower speeds.

There are a total of five fan control relays.
Three primary relays in the fuse/relay box, and two secondary relays, mounted on the driver side of the radiator support, all by themselves.
These two relays are where you want to tap in at.

You can wire in an "override" circuit to trigger the low speed circuit without triggering any PCM codes.
The wire you are after is Lt. Green, with violet stripe. It goes to both relays, so it doesn't matter which relay you uncover the wiring to, they are on the same circuit.
Tapping into this wire to a manual switch and/or thermostatic switch will allow you to trigger the low speed circuit without triggering any codes.
I just trimmed a spade terminal that I pushed into the socket terminal under the relay.
Didn't have to even splice into the wire itself.

One thing to note is, that when this override is engaged, the fan basically becomes just a two-speed unit, low and high speeds only.
If the override circuit is engaged, and the PCM commands a medium fan speed, high speed will result.
If the override circuit is not engaged, the fan will operate in its normal 3-speed configuration.

I bought a small thermal switch with a 160 deg. on, 145 deg. off setting, and glued it to the radiator core.
Basically, one side of the switch taps into the lt. green/violet wire, the other side to chassis ground.
Now just because the fan switch I used turns on at 160° does not mean the engine will operate at 160, just that the outlet side of the radiator will likely not exceed 160 by much.
The engine operating temperature will still be governed by the coolant thermostat.
The peak temperature may drop by about ~7° when stopped, or in stop-n-go traffic.
A manual switch could also be tapped into this same circuit.

Heres a diagram of the cooling fan circuit:
I added the arrows to indicate current flow, from positive to negative.
In the upper right corner of the diagram, you can see where I marked in the modification.





Keep in mind this is for a 2013 1.4T model, so I can't guarantee it is correct for the 1.8L or other model years, but I suspect it may work for others as well. Just not certain of it...

 

[BigLee]

They clearly over-engineered the cooling fan circuit, and created a complex solution to a simple problem.
They could have eliminated the two secondary relays altogether if they had just added one more grounding driver circuit to the PCM.
I'm willing to bet there's an unused driver in the PCM already, that could've been used to control the three primary fan relays directly.

 

[Papasonic]

I get that the fan circuitry is complex, but I don't understand the advantage of the modification; could you explain the advantages of performing this modification?

 

[JesusTheAgnostic]

Uh what? The only time I hear the radiator fan turn on is when I forget to plug the maf back in like an idiot. So I'm confused as to why you're modifying it.

 

[BigLee]

Sorry, i thought my objective here was kinda obvious.
I edited my original post to make this clear.
I'm modifying it to turn the fan on at a lower
temperature than stock, by using a thermal switch sensing the radiator core temp to turn on the low speed fan.

 

[Natesriv]

Hotter engines run more efficiently. Cooler isn't better for combustion cycles & such...
IMHO

 

[BigLee]

Hotter engines run more efficiently. Cooler isn't better for combustion cycles & such...
IMHO

In theory, yes. In practice, not so much.
The gains in fuel economy between say, 195 deg. and 225 deg. would be difficult to measure.
And it's pretty obvious that the detonation threshold gets crossed pretty easily on these cars on 87 octane pump gas, as the programming is pulling ign. timing back some from optimum settings, which suggests that operating a little cooler might actually improve fuel economy a bit.

Now this mod alone only drops the peak engine temps from about 224° to about 217°.
But it can drop temps on the transmission oil cooler substantially, by as much as 60°.
One thing is certain though, the higher operating temps and cooling system pressures on these engines pushes several cooling system components to the edge of their durability. Water pumps, water outlet housings, surge tanks, hoses, ect., are all common, even repeat failure items on these cars.
I've even seen a couple of popped radiators on them.

 

[JesusTheAgnostic]

Okay, no I get that you wanna mess with the fan. I don't get why though. Have you noticed how sensitive the engine is to pulling current? Besides It is as hot as the devils anus in El paso but I only ever hear the fan turn on when I forget to plug in the maf. Though to be fair it would indeed probably be a good idea during the summer.

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[BigLee]

You probably only hear the fan when it's on high.
Low speed is very quiet, and would be quite difficult to detect from inside the car, thus low/med speed are probably operating without you being aware of it much of the time.

With as many cooling system components that are known to have issues on these cars, plus the fact that the PCM is clearly detuning the 1.4 for regular/midgrade, possibly even some for premium grade fuel, I think it would be wise to cool things off just a bit.

 

[mja]

Hmm, seems like a cool mod to turn on the fan earlier as these things age. I agree with what Jesus said, the harness/ECM doesn't like modifications. Have you done it yet, are you throwing codes?

Couple things, do you have proof this is turning on the low speed fan under certain conditions. Also, fan speed settings can be adjusted in the ECM, why not that?

As others said, higher operating temps are governed by the thermostat, the fans only make those temps more stable. Does yours have an issue with overheating?

I don't agree that these motors 'detonate' especially often on 87. KR pulls timing at low load/ high input, or high stress (peak torque or peak power) as with any motor. If thats actually happening it sounds like an engine mechanical issue, not a fan speed issue.

 

[BigLee]

Yes, this mod has been done to our car, and has been proven to work as I described.
And no, our car did not have an issue with overheating.
The coolant thermostat has a std. operating temp of 217°F, and if the A/C compressor is off, the PCM doesn't typically turn the low speed fan on until 224-225°.

If you study the fan wiring scematic, you will see that the PCM has no direct connection to, or means of sensing what is happening to the wire I tapped into, thus no code is triggered.
And since the the engine won't drop below the coolant thermostats regulated temp, no low temp code is set either.

AND yes, these engines do indeed experience some ammount of knock retard on 87 oct.
Why else would switching to 93 oct. Fuel alone make your avg. fuel economy jump by 3-4 mpg, then go back down by the same ammount when going back to regular?
Similar gains have been reported by and discussed here by other forum members.

Think about it: This is a small displacement, hot running turbocharged engine with 9.5:1 compression ratio, with hypereutectic pistons, in a not so light car.
Detonation on 87 oct. fuel is almost a given...

 

[mja]

So with the switch installed, the motor will cool slightly quicker in traffic when the thermostat opens up? Could help for towing or hot summers, thanks for the writeup!

Yes, KR is normal but if seeing KR constantly on pump gas in low load/low demand setting, somethings wrong.

 

[BigLee]

Yeah it could help with towing in some cases, especially if lots of stop n go driving is involved.
On the highway, maybe to a lesser extent.

As for KR, no you won't likely get it under lighter load conditions, but many would be suprised at how little it takes to get these vehicles into positive manifold pressure. Just keeping pace with traffic will easily do it.
When you have a small, hot operating engine, pushing a not so light car, you tend to get into boost conditions quite regularly, and that will easily push regular fuel past it's detonation threshold with optimized spark tables.

It wasn't too many years ago that an engine like this would have operated cooler, had a lower static compression ratio, and been labeled "premium fuel only."
The's engines really should be recomended for premium fuel only, but the powers that be probably figured that it would be a selling point to
rate it for regular, and just let the PCM detune it as necessary to tolerate regular fuel.

 

[JesusTheAgnostic]

The car in Stock form outputs the same horsepower on 87 91 93 86, whatever you give it. If you want to cool things down you'd probably be better off injecting some meth

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[BigLee]

The car in Stock form outputs the same horsepower on 87 91 93 86, whatever you give it. If you want to cool things down you'd probably be better off injecting some meth

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Not really.
Using 87 oct. definetly hurts both fuel economy and WOT performance.
The PCM will curb spark knock by retarding ign. advance, and peak boost if necessary to control it.
With these engines, you will make performance and economy sacrifices on low grade fuel...

 

[JesusTheAgnostic]

Dyno sheet? It's supposed to output 138 regardless. It does seem to like 91 better than 86 though. No MPG gain though

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[BigLee]

No dyno sheet, just "butt dyno" results, sorry.
There is a reason why it feels better on 91 grade...
If my wife would allow me to, I would have ran it on both grades at my local dragstrip...
But she thinks I'm gonna do burnouts with her car like I do with my truck and my Corvette, even though I've tried to convince her that isn't even necessary with her car.

 

[mja]

There are a lot of guys on here who have tuned in the past, currently tune, or datalog. To tell these people that KR comes on constantly is like

GM ECMs for the last few decades have all had multiple spark maps for low and high test gas. Ign retard on KR sensor isn't common unless WOT or high torque demand at low load.

& Jesus, the meth inj wouldnt cool the motor as this mod would cool down coolant slightly quicker. That would cool the combustion chamber or IAT if placed in or before charge tubes.

 

[JesusTheAgnostic]

Mja bro I'm not sure if you're on my side or not lol. I need some meth because the only negative effect I've noticed from heat is decreased power output. Don't really care about MPG since the car hits 40 regardless of temperature if you drive it right.

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[mja]

Mja bro I'm not sure if you're on my side or not lol. I need some meth because the only negative effect I've noticed from heat is decreased power output. Don't really care about MPG since the car hits 40 regardless of temperature if you drive it right.

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I take no sides lol. I kid, BigLee's electrical switch pulls more air through the radiator and would help the coolant temperature drop quicker when the thermostat opens up. I'm impressed it doesn't thow a code & glad we have more electrical savvy guys here. There are plenty of people on the forum who don't want to change or tune fan settings in the ECU to get similar results. This mod would be good for cruising around in traffic with the A/C on a hot day, or for towing, things that make coolant temp creep up. Coolant temp controls how hot the block and head get, when the coolant gets too hot it stresses first the gaskets and the Aluminum parts of the motor (head/head gasket on the 1.4T)

What you're looking for is unrelated from that, you don't want a way to cool the block & head quicker, but just cooling the combustion chamber or intake air charge. Methanol is good at both of those things. Look up lower temp thermostats, and how they make power in a carbureted engine.