MG TF Cooling plus Fan Control Modification - MG-Rover.org Forums
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post #1 of 16 (permalink) Old 28-02-2017, 02:04 Thread Starter
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MG TF Cooling plus Fan Control Modification

I have also posted this as a reply to a similar thread but I thought it might be useful as a thread in its own right. Regarding the radiator cooling fan issues. I live in Perth, Western Australia and, as such, keeping my 2003 MG TF from overheating is an even more important issue to me than to those who live in cooler climes. For example, summer temperatures often reach in excess of 40degC so here is what I have done for some peace of mind.

First of all, after replacing the cylinder head gasket I refilled the cooling system with waterless coolant. I used Liquid Intelligence 115 which has a boiling point in excess of 190degC. It works on the same principle as the Evans product. I like the fact that it does not corrode the inside of the engine and the fact that it does not stress the hoses by creating steam pressure. Yes, it is much more expensive than water/glycol coolants.(Waterless Coolant | Car Radiator Coolant|Radiator Coolant Flush)

Secondly, I suspected that my radiator fan was not cutting in early enough and noticed the temp gauge rising as I sat at traffic lights on a hot day. I read the many threads on the forum about the issue. As a result of all this research I made the following simple modification to my car. I fitted a single push switch wired to my engine temperature sensor. It works like this. The MG TF cooling system employs a fail safe system whereby, if the sensors fails, the wiring breaks or the sensor becomes disconnected, the radiator cooling fans automatically come on. In fact to test the circuit, you start the engine, pull the plug off the sensor and the fans start up. So to simulate one of these failures I wired a "normally closed", spring return push switch in series with the sensor. The switch cost me 4 dollars (about 2 quid max). To avoid running the wires all the way to the front and then under the carpet onto the dashboard I fixed it to the interior panel behind the driver and passenger seat. I'll try and attach a picture.



So now, when the engine is running I push the switch and, after two seconds, the fans come on. They stay on until the ignition is switched off (this is by design in the fail safe circuitry). I now have peace of mind and some control over my engine cooling. I recommend the simple mod for all those who have similar concerns or circumstances.
PS I am waiting a reply from James regarding how the ECU interprets the sensor info after the fan is forced on.

Last edited by Roverlike; 28-02-2017 at 04:10.
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post #2 of 16 (permalink) Old 28-02-2017, 06:58
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Not sure why you decided to mount the switch in that position. The switch may have been cheap, but it looks a bit odd in my opinion.

You mention not having to run the wiring through the cabin to the dash, but you had to go past the dash to get to your switch if the wiring comes from the front rad. You could easily have used one of the dashboard switch blanks to create a more 'OEM look'.

Or do you mean the switch operates the engine bay cooling fan, not the radiator fan?

Even then I would have used a bit more cable to improve the look.

Just my tuppence.

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post #3 of 16 (permalink) Old 28-02-2017, 07:26
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Not sure why you decided to mount the switch in that position. The switch may have been cheap, but it looks a bit odd in my opinion.

You mention not having to run the wiring through the cabin to the dash, but you had to go past the dash to get to your switch if the wiring comes from the front rad. You could easily have used one of the dashboard switch blanks to create a more 'OEM look'.

Or do you mean the switch operates the engine bay cooling fan, not the radiator fan?

Even then I would have used a bit more cable to improve the look.

Just my tuppence.
It looks to me like he's tapped into the coolant sensor in the engine bay, not tapped into the rad fans.
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post #4 of 16 (permalink) Old 28-02-2017, 11:00
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Yeah, I think he is fooling the system into thinking the car is overheating, rather than just powering the fans.
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post #5 of 16 (permalink) Old 28-02-2017, 11:27
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It looks like the switch is used to disconnect the sensor, this would fool the ECU into thinking that the sensor had failed and put rad fan on and the engine bay fan on if the car is a late TF.
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post #6 of 16 (permalink) Old 28-02-2017, 13:08
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So long as you're not doing this on a regular basis, there's no reason to think this won't work.

However if you are doing this on a regular basis, get ready for your fans to burn out as they run like mad when you disconnect the sensor.
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post #7 of 16 (permalink) Old 28-02-2017, 15:11
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I just do not see the point of the mod other than the waterless coolant. I would expect the various sensors to work as fast as they needed to so as to turn off and on fans, with the thermostat opening once the temp rating was exceeded.
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post #8 of 16 (permalink) Old 28-02-2017, 18:11
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ive commented on this sort of topic a lot...

of far more importance is to know that the thermostat works, and that the heater and rad matrix has no blockages.

thats because if the thermostat doesnt open properly, the heater matrix isnt flowing properly and the rad isnt flowing properly.. ( extreme circumstance i know... but its possible) then the coolant will choose the easiest route... and that is the hot circuit.. and it has no cooling..

it dont matter you turn all the fans on...

your cooling still water... not moving water.


there is no flow meter on the mgf.. that would tell you the flow through the rad return pipe to the pump is too low.. and warn you of blockages in the cooling system....


i think installing a simple flow meter with some window of adjustable accuracy.. would be beneficial. much better than being able to turn the fans on or off manually... tell me when im not moving enough coolant for the ambient temperature i have.

so.. its 27 deg C outside.. quite common in the uk.. and the road is getting hot... the tarmac gets sticky in places...

suddenly at traffic lights while i sit in a que of cars on a hot road the flow sensor starts beeping and flashing an led... if i rev it stops... thats telling me at idle, stationary, the engine isnt circulating the same coolant as it was when i set it up.. but does when i increase the revs... so something has changed in the return flow... its telling me that... the rad might have a blockage, the thermostat might have stuck... something has decreased the flow rate.. now its sometimes outside its set window..


?

of course the flow sensor could be telling lies, maybe its blocked... but at least its telling me something is wrong.

flow sensors are as important as thermostats i think... if they work properly they are the difference between cooked engine.. or not.

ie.. your fans are all on... but still the temperature gauge is rising... you dont know why.... a flow meter might tell you its not HGF its a blocked rad.. or a stuck thermostat.. you have low flow in the return pipe..

Last edited by Incony; 28-02-2017 at 18:32.
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post #9 of 16 (permalink) Old 02-03-2017, 17:45
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On a 2002 TF160 should disconnecting the air temperature sensor start the cooling fan? It doesn't on mine.
Disconnecting the engine coolant sensors as shown on this thread does make the cooling fan work, I was under the impression that it was later cars that work like that. Rather than 2002 ones?
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post #10 of 16 (permalink) Old 03-03-2017, 13:06 Thread Starter
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Feedback from the bloke who created the mod

Thanks to everyone for reading and commenting on the mod. I'll try and answer a few queries.
No idea if this works on anything other than a TF 120.
As to why I went to the trouble you need to know the feeling of sitting in a car in 40 deg heat, at a stand still, watching your engine temp creep up and wondering if your fan sensor has failed.
I admit it is not the classiest switch position. But now that I know it works, and the MG forum audience knows it works, the next person, maybe me, will use the redundant switch slots on the dash. Fair comment though.
Yes, it is wired to the sensor, not the fan so 1 metre of twin flex was enough.
Finally, the heat here in summer means the rad fans are generally working a great deal more than Euro climes, so yes, I imagine we burn out more fan motors in this neck of the woods.
Anyway, great forum chaps. Love the banter and the fearless criticism. Happy motoring. Mick
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post #11 of 16 (permalink) Old 03-03-2017, 21:51
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Originally Posted by Mick Lampard View Post
I am waiting a reply from James regarding how the ECU interprets the sensor info after the fan is forced on.
When the ECU receives a high signal from the coolant temp sensor it triggers the radiator fan. When the ECU receives no signal from the coolant temp sensor it assumes the coolant may be hot and again runs the rad fan.

In a separate operation the ECU sets the fuelling map based on the perceived temperature of the coolant. The ECU also uses other inputs such as road speed and throttle body opening and info from the pre cat lambda probe.

There are also two styles of injection, closed loop where the injectors fire just enough fuel and only into the cylinder that needs it or open loop where all the injectors give a full shot every revolution. When cold (below about 45') or when accelerating the ECU runs an open loop. If the ECU doesn't know how warm the coolant is because it isn't getting a signal from the coolant temp sensor it assumes the engine is hot and fires the rad fan (as I said above), it also assumes the coolant is cold so uses open loop fuelling.
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post #12 of 16 (permalink) Old 04-03-2017, 00:27
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Mick, sounds like you've come across the fact that the rad is under-rated for the car, I for one commend your mod. 40 deg C isn't something we get often - if ever! over here, so good on ya! Maybe the temp sensor or mems uses a differential rather than absolute before kicking in the fans, I don;t know.
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post #13 of 16 (permalink) Old 05-03-2017, 05:28 Thread Starter
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When the ECU receives a high signal from the coolant temp sensor it triggers the radiator fan. When the ECU receives no signal from the coolant temp sensor it assumes the coolant may be hot and again runs the rad fan.

In a separate operation the ECU sets the fuelling map based on the perceived temperature of the coolant. The ECU also uses other inputs such as road speed and throttle body opening and info from the pre cat lambda probe.

There are also two styles of injection, closed loop where the injectors fire just enough fuel and only into the cylinder that needs it or open loop where all the injectors give a full shot every revolution. When cold (below about 45') or when accelerating the ECU runs an open loop. If the ECU doesn't know how warm the coolant is because it isn't getting a signal from the coolant temp sensor it assumes the engine is hot and fires the rad fan (as I said above), it also assumes the coolant is cold so uses open loop fuelling.
Thanks James. So if I am reading this properly, as the sensor is in circuit the whole time except for the moment I press the button, the ECU is receiving temperature sensing data and therefore sending the correct amount of fuel to the injectors.
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post #14 of 16 (permalink) Old 05-03-2017, 19:56
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Thanks James. So if I am reading this properly, as the sensor is in circuit the whole time except for the moment I press the button, the ECU is receiving temperature sensing data and therefore sending the correct amount of fuel to the injectors.
if the switch " spikes the signal" (and switches spike when they close and open..) then the answer is no, if the ecu see`s that spike..

at the point a switch opens or closes.. there is a point where its neither fully closed or fully open but electricity can flow across the gap.. its partial because its not fully connected nor disconnected. its a high/ low resistance just at that point... and that changes the complete thing.. it becomes two things in union.. a resistance circuit in parallel and connected to the ecu..

if i wanted to turn the fans on or off.. i would use the fan direct feed... nothing that the ecu uses to sense.. i dont want to change anything the ecu can see.. i want to change what the fans do.


the easy solution.. isnt the easiest consequence,,

i think that using an ecu sensing circuit is the wrong way to influence turning the fans on or off... unless one is moving the sensor.. physically.. and so changing its environment.. ie if you move the sensor to a hotter place... it turns on sooner...

one needs to use an ecu output circuit... there - the ecu has already made its decision.. you just change that.. not what it senses before it makes its mind up//

?

you are not interested in the ecu making its mind up what to do... you want to change what it decides at any time before or after it decides... and not change its decision... just its consequence,, and that should not include the ecu.. you dont care what its decided. The ecu controls many things based on its decision.. but you just want to change one... and one only.. what fans are on or off when you press a switch.. that cannot change what the ecu can see... but changes its consequence.

THe ecu has decided the fans are off.. its also decided the air fuel ratio, and so determines the signals it sends..


you dont care about that... you are not altering what the ecu signals... you change what those signal do.. and in the case of the fans... you decide .. not the ecu.. if they are on.. or off. You dont care that the ecu thinks its cold.. or hot... and dont change what the ecu thinks.. it can carry on thinking what it wants... and so.. because you turn the fans on... it might see that the temp senor now can see something different.. the coolant is cooler... so it it changes the air fuel ratio... you dont care about that.. your choice was to make the fans run regardless of the ecu..

Last edited by Incony; 05-03-2017 at 20:37.
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post #15 of 16 (permalink) Old 05-03-2017, 20:47
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Thanks James. So if I am reading this properly, as the sensor is in circuit the whole time except for the moment I press the button, the ECU is receiving temperature sensing data and therefore sending the correct amount of fuel to the injectors.
I can't say but if your momentary signal break is enough to run the fan continuously I'd be worried about what else it is doing. It'd be worth running a scanner to see what it's doing.
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post #16 of 16 (permalink) Old 05-03-2017, 22:36
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If the radiator fan is anything like the engine bay fan, then the circuit to switch on the fan relay is controlled by the ECU earthing the circuit. You could just have a simple on/off switch to earth the circuit put into the line from the relay, you can then turn the fan off again and give control back to the ECU should it be cooler.
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