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Old 11-15-2012, 12:08 PM   #1 (permalink)
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My fan override switch

Sharing in case anyone else could benefit...

I personally don't want the engine radiator water temp to get over 100degC before the fans turn on to bring it back down to the 83degC thermostat setting. To me, any extra heat is bad for the engine (especially pre-liner changes) and all the accessories attached to the engine and in the engine bay. I have never had a car that the ECU allows for a 30degF swing like that.

I was controlling the fans by turning on the AC compressor because if the AC is on, the fans are on. But after servicing my AC so it worked super well, I found that I was freezing in the cabin just to keep the engine at the right temp.

So have I added a relay and a switch in the cabin so I could turn on the fans whenever the key was in Accessory mode or Ignition. I didn't want to be able to turn on the fans without having the key in the ignition because I tend to forget things like that and then I would kill the battery. To make this happen, I had to add another relay. See attached PDF for my wiring.

All of the work done was in the relay box in the front cabin, and I ran 2 wires through the existing grommet in the front wall to get the switch in the cabin. I mounted the switch on the bottom edge of the dash so it's easy to reach, but also invisible. I just hot glued the switch since the switch had a lot of surface area for gluing, and the heat is low in that area so the glue won't melt, and the glue doesn't have to work that hard to hold switch in place, and it's glues super fast so I could get on with driving it. However, I am still recovering from the burn on my hand that the dripping hot glue gave me, so wear a glove. See pic of switch mounting.

In case you are wondering, if anything in my system fails, the fans will go back to working the way they did before the mod, so there's no worries there.

If you're not into electrical wiring diagrams and soldering, you should get someone to advise you in person. With the diagram, they will know what to do.
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Last edited by lotusespritse; 11-15-2012 at 04:38 PM.
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Old 11-15-2012, 12:58 PM   #2 (permalink)
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I have done a similar thing with mine, but hot-wired the heated rear window switch ( which I never use ) to switch on the fans instead. Again all wiring is done at the relay box and is just a case of removing the heated rear window relay and adding a wire jumper link to the fan relay coil. This way you have the switch right in front of you and it's illuminated when on too.
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Old 11-15-2012, 01:13 PM   #3 (permalink)
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You never used the heated rear screen in down under?
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'88 Excel SE - monaco white | '87 TurboEsprit S4-Emme-Edition - calypso red | '10 Evora - starlight black
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Old 11-15-2012, 02:20 PM   #4 (permalink)
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Quote:
Originally Posted by stevem View Post
I have done a similar thing with mine, but hot-wired the heated rear window switch ( which I never use ) to switch on the fans instead. Again all wiring is done at the relay box and is just a case of removing the heated rear window relay and adding a wire jumper link to the fan relay coil. This way you have the switch right in front of you and it's illuminated when on too.
Where is that heated rear window relay on your car? I don't have one in the front compartment according to this diagram. US spec 98 V8.

I just looked and you have an 88. I think it's very different electrically.


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Old 11-15-2012, 05:45 PM   #5 (permalink)
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This seems to be a popular mod. There is a down-side to this so be aware. The fan circuit was not intended to run continuously. When moving over 35 MPH the fans are not necessary. Running the fan circuit continuously never allows the wiring, relays, and motors any chance to cool down. It's called a "duty cycle". At 100% duty cycle you can overheat things and work the alternator harder than it was intended. Like most welding machines, they are not meant to work continuously, in fact, many are rated at 50% duty cycle, which means it has to be off as much as it is on. The motor's efficiency increases as it gets hotter. Bigger Delta T. The problem is the materiels the motor is constructed of can only get so hot before they fail. The other problem is the clearances are all set up so the parts can expand but only to the limits of the cooling system's capacity to remove heat. Bottom line, you should not allow the fans to run continuously for long periods of time. Otherwise you are just trading overheating the motor for overheating and overloading the electrical system. If you find your motor is running too hot the radiator is plugged up either on the air side or the water side or both. Maybe some kind of timer circuit like the rear window defoger on many cars use.
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Old 11-15-2012, 06:17 PM   #6 (permalink)
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David,

You're forgetting that if the AC is on, then rad fans are on. Down where I live, that means the AC is always on for 7-8 months of the year during the day, and most nights. If you check the circuit diagrams you will see this switch attached to the AC system that overrides the ECU's fan control.

So if the fan circuits can't take that, then you have a system that needs a wholesale redesign.

My cooling system is in tip top shape. Newly recored radiator with an extra row, 3 new Spal fans, new thermostat, new silicon hoses, inspected water pump, new header tank, fresh 50/50 premix.

The only flaw is the ECU's programming for turning on the fans at such a high temp if the AC is not running.

As an engineer, I know heat is the enemy of many of those things under that trunk lid.

Phil



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Old 11-15-2012, 08:10 PM   #7 (permalink)
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On the 4cyl you have to be sure to use the ECU temp reading and not the dash gauge to decide if you are running at the desirable temp. The gauge tends to be less accurate and does not reflect the same data as the ECU. I don't know if this is an issue on the V8.

The temp hitting 100C is not significant to any engine component or the "water" assuming you are running antifreeze.
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Old 11-15-2012, 08:34 PM   #8 (permalink)
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Originally Posted by 89.5 Esprit SE View Post
The temp hitting 100C is not significant to any engine component or the "water" assuming you are running antifreeze.
Then why is the thermostat not spec'd to open at +100C?

Doesn't make sense really.

I'm going to continue to run my car at the lowest temp on the spec range.
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Old 11-16-2012, 05:25 AM   #9 (permalink)
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You are correct, the cooling fans run when the compressor for the A/C is going. BUT, the compressor is also supposed to cycle, so when it stops the fans will also stop. Heat is not all bad, you just do not want too much of a good thing. It does make the parts age quicker, the rubber mostly. The whole car was designed for this, if you don't want to wear it out then don't drive it! Change the fluids more frequently if you are that worried about wear. If the fans cycle then you are not overheating the motor. Too cool is also not good.
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Old 11-16-2012, 05:50 AM   #10 (permalink)
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I suspect that the reason for running the temps high is for emissions purposes. Higher temps give a more complete burn but obviously less power. The correct answer to this problem is a tune to adjust the temp that the ECM turns on the fans. Not sure how easy this is on the V8 ECM but I'm guessing its not that easy...on a 4cyl ECM this is trivial with a custom PROM.

I do like the clean install on the fan switch.
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Old 11-16-2012, 05:55 AM   #11 (permalink)
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Originally Posted by jtrealty View Post
You are correct, the cooling fans run when the compressor for the A/C is going. BUT, the compressor is also supposed to cycle, so when it stops the fans will also stop. Heat is not all bad, you just do not want too much of a good thing. It does make the parts age quicker, the rubber mostly. The whole car was designed for this, if you don't want to wear it out then don't drive it! Change the fluids more frequently if you are that worried about wear. If the fans cycle then you are not overheating the motor. Too cool is also not good.
David Teitelbaum
The compressor doesn't cycle here in TX! It's full on baby! That's not my guess, that's my observation living here in the Dirty South with the Esprit.

Lotus engineers are great, but not perfect. Plenty of examples of things that don't make sense. It makes sense for me to run the car at the lowest in-spec temp. If you don't like it, don't drive my car! (silly comment to not drive my car if I am not happy about the fans....)
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Old 11-16-2012, 05:56 AM   #12 (permalink)
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The correct answer to this problem is a tune to adjust the temp that the ECM turns on the fans. Not sure how easy this is on the V8 ECM but I'm guessing its not that easy...on a 4cyl ECM this is trivial with a custom PROM.

I do like the clean install on the fan switch.
Reprogramming the ECU would be my first choice. Not many tuners working on this car though...

Thanks on the install!
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Old 11-16-2012, 06:19 AM   #13 (permalink)
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Quote:
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Maybe some kind of timer circuit like the rear window defoger on many cars use.
David Teitelbaum
David,

In another car, I used the rear defroster switch as an activation for a nitrous bottle heater. The timed circuit on the defroster was perfect in that application. It made sure that I never left the bottle heater on too long. I also had a remote pressure gauge to monitor nitrous pressure. So, if one cycle of the defroster wasn't enough, I could hit the button again to continue bringing up the temps/pressure of the n20.

simiarly, the defroster timer sounds like a great use for a manual fan switch, too. I haven't come across any heat issues with my Esprit...... but I'll keep this in mind in the future if I need a fix.
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Old 11-16-2012, 07:41 AM   #14 (permalink)
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An ideal solution that would not require an ECU reprogram would be to add a good old fashion otter switch to turn on the fans at a temp such as 85degc. It wouldn't be that hard to plumb something into the radiator pipe connections in the front of the car, and the electrical is ready to accept that with my mods.

Last edited by lotusespritse; 11-16-2012 at 08:08 AM.
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Old 11-16-2012, 11:22 AM   #15 (permalink)
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This sort of thing looks like an attractive option:

Electronic Fan Controller 25mm from Merlin Motorsport

Full control over the fan temp, and only need to splice it in to the existing hoses.
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Old 11-16-2012, 01:22 PM   #16 (permalink)
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Originally Posted by lotusespritse View Post
Then why is the thermostat not spec'd to open at +100C?

Doesn't make sense really.

I'm going to continue to run my car at the lowest temp on the spec range.
If the fans are set to come on at a temp like 95-100, then the engineers did that for a reason. If you drive your car hard it will tend to run at the higher temps. So I think it is quite safe. Most modern turbos will limit boost if the temp is too cold not too hot. The 4 will not allow full boost below about 82. Clearly you don't want to run too hot, and there are pros and cons of both ends, but if the engine is designed to run at a certain temp then it should be run at that temp.

You do need to ensure that everything is operating correctly and that you have the proper thermostat, since the latter is mechanical.
If the thermostat openened and closed at your ideal operating temp then it would be cycling very frequently and you would not get proper radiator flow which is how you get proper cooling. Remember that the fans don't generally operate to keep the radiator cooling except at slow road speeds or very high ambient temps. If you are driving at 80mph your fans won't add too much air flow.

Randy
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Old 11-16-2012, 01:37 PM   #17 (permalink)
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Originally Posted by 89.5 Esprit SE View Post
If the fans are set to come on at a temp like 95-100, then the engineers did that for a reason. If you drive your car hard it will tend to run at the higher temps. So I think it is quite safe. Most modern turbos will limit boost if the temp is too cold not too hot. The 4 will not allow full boost below about 82. Clearly you don't want to run too hot, and there are pros and cons of both ends, but if the engine is designed to run at a certain temp then it should be run at that temp.

You do need to ensure that everything is operating correctly and that you have the proper thermostat, since the latter is mechanical.
If the thermostat openened and closed at your ideal operating temp then it would be cycling very frequently and you would not get proper radiator flow which is how you get proper cooling. Remember that the fans don't generally operate to keep the radiator cooling except at slow road speeds or very high ambient temps. If you are driving at 80mph your fans won't add too much air flow.

Randy
I clearly don't have anything better to do but debate fan on/off logic...

"If the fans are set to come on at a temp like 95-100, then the engineers did that for a reason."

Same reason they designed the radiator fins to clog up? Same reason the whole rad/fan setup needs to be replaced to really survive for hot weather climates? Same reason they designed liners to fail? Same reason they kept the crap Renault gearbox?

They're not perfect. And I do think vbtodd's theory of letting the car run hot at idle speed to improve the ability to pass emission is a real possibilility, and not that they were thinking they could make sure the car would last past the whopping 2 year warranty period by making it run hot at slow speeds.

"If you are driving at 80mph your fans won't add too much air flow."

Great point. So if air is blowing through the front radiator opening, the fans are going to draw very little current since they don't have to work to push the air. Basically, you are turning off the fans even when they are on at high speeds. That's how electric motors work. No load = no power to drive them. In fact, if the air flow was strong enough, it would charge the battery (wind mill). So there's David's duty cycle problem solved!

Keep in mind the AC switch just checks the pressure level in the AC system to know it's on and then turns on the fans regardless of what the engine wants. So the AC has the fans on all the time even if your driving at 70mph when you live in Texas and you have +100degF and a huge greenhouse for a front windshield.

But, hey, run it hot if you like!
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Old 11-16-2012, 03:12 PM   #18 (permalink)
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The fans will be turned off above around 35 mph on most cars when being demanded for A/C. I don't see the V8 being any different especially since this is what the 4 cylinder ecu does.

I too personally prefer to have the fans coming on at a lower temperature that is closer to the thermostat temperature. Easy to sort on the 4 cylinder ecu's with the removable memcals, not so easy on the V8 ecu's with the surface mount chips.
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Old 11-16-2012, 03:19 PM   #19 (permalink)
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The V8 is different. The ECU is out of the picture when the AC sensor turns on the fans. That AC sensor is like an otter switch. No way for the speed to be considered.

Keep in mind this is a Lotus! Jeremy Clarkson didn't affectionately call them the "Bob a Job Boys" for nothing.


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Old 11-16-2012, 03:24 PM   #20 (permalink)
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Here's that switch. It grounds the coil in the fan relay to turn on the fans when the AC compressor pressurizes the system regardless of what the ECU thinks.


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