POBC - Emerald ECU controlling fan query

[skydragon]

I've a modded 1.8K with no heater and a standard grey Land Rover 82DegC PRRT fitted and up until now I've used the standard radiator thermostatic switch to turn the cooling fan on/off.

 

I decided last week to wire up the emerald ECU to control the fan instead via a relay.

 

All works ok from an electrical point of view....but there is a puzzling issue that I just can't understand...can anyone please assist?

 

In the past, I've been used to see the fan come on with an indicated coolant temp of around 97 degC and go off at around 92DegC (measured on my digital dash and calibrated). The Emerald coolant temp and my digital dash temp are within a degree or so of each other....so wanting to match the previous settings as a starting point, I set the emerald ecu to switch the fan on at 97 and off at 92.

 

I've described below what is now happening....and I'm confused *confused*

 

I start the car and let it warm up. The outdoors temperature today was approx 9 Deg C. Eventually the coolant temp gets to 97 DegC and the emerald switches the fan on - all ok. However at this stage the radiator core/bottom is still stone cold and what now happens is, the fan continues to blow, whilst the coolant temperature continues to climb to 100. In effect the PRRT never opens and due to this there isn't any coolant flowing through it (?) and as a result the radiator actually does nothing to cool the car even though the fan is on.

 

If however, I disconnect the fan for a moment and let the car warm up to around 97DegC and wait for a minute, the radiator then starts to slowly warm up as coolant flows through it (The PRRT has opened) - If I then reconnect the fan once the radiator core is hot, the fan will now cycle on/off controlled by the Emerald ecu perfectly ok and it controls the coolant temperature ok, as you would expect.

 

Question is;

 

- why does the fan coming on before the PRRT has first opened, then stop the PRRT from opening at all, even though the coolant in the bypass circuit is hot?

 

- why does the PRRT seem to work all ok, if I first let the radiator warm through by temporarily disconnecting the fan and then reconnecting it.

 

- I could try setting a higher switch-on point on the Emerald ecu, but that would then make the fan switch-on point too high.

 

I've reconnected the standard radiator thermostatic switch and it all seems to work ok, but I'd really like to have better control of the exact fan switching points via the Emerald if possible.

 

In some ways switching the radiator fan by measuring the coolant exiting the engine is not the best idea, because what you really want to do is turn the cooling fan on when the radiator itself is hot, not the engine.

 

Any ideas??

 

Thanks,

 

 

 

Edited by - Skydragon on 3 Mar 2013 19:55:16

[skydragon]

bttt - any ideas?

[Bio]

Sounds like the fan is cooling the system a little early and not allowing the thermostat to open. The sensor now switching the fan is in the water rail not in the top of the rad, could this be heating up quicker than the rest of the system.

 

John

[skydragon]

John - But if the the bypass circuit is hot and above 82 Deg C, surely the PRRT should open irrespective of how hot/cold the radiator hose output is ?

[Rob Walker]

If you are seeing 97c then the stat should be well open and water should be circulating around the rad. If it is not then the system could be airlocked or the stat is faulty and the emerald is sensing circulated coolant in the bye pass loop only.

 

Rob

 

Edited by - Rob Walker on 4 Mar 2013 10:25:18

[Jonathan Kay]

Can you swap the feeds from the sensors to see where the difference originates?

 

Jonathan

[skydragon]

The temp sensors are reading accurately. There is no difference between what my ECU is seeing in terms of temperature and what my dash display is seeing in terms of temperature.

 

I'm 99.9% sure there is no airlock.

 

I've just removed the PRRT unit and tested it in a pan of water, with a thermometer and it starts to just open at 82 DegC and is fully open by 88 Deg C.

 

So the question now is, why does having the engine fan on stop the PRT thermostat

opening?

 

I guess it could be due to the cold radiator being right next to the PRRT unt (there is only approx 4" of pipe between radiator output and PRRT unit) and as such this cold coolant is cooling the PRRT down so it never gets up to above 82 DegC ?

 

Looking inside the PRRT it has a jiggle valve in it, so there is always a very small flow of coolant through the radiator and through the PRRT thermostat.

 

If this is the case, I think what is happening is this; - When I am travelling along at speed the radiator is not doing anything as it's output is very cold and it's preventing the PRRT from opening, even though the bypass loop through the PRRT is hot. When I stop the car and let it idle the PRRT doesn't open until enough hot coolant has bled through the radiator via the PRRT jiggle valve hole, to then allow the PRRT to open up. This time delay in the radiator warming through means the engine temperature climbs to near 100 before the PRRT opens up - but once the PRRT has opened up for the first time, the cooling fan cutting in and out doesn't then cool the whole circuit enough to stop the PRRT working ok whilst the car is static.

 

The above situation means that I can't use the Emerald to control the fan. It also means that my car will heat up to around 98-100 Deg C before the PRRT will open up, for the first time - but if the car is stood still, the fan will then control the temperature and cycle it between 97 and 93 DegC.

 

None of the above is doing any harm to the car....but when fitting a PRRT I had presumed that it would keep the temperature stable and not allow temperature fluctuations as above.

 

I'm not sure the above would happen on a hot day - perhaps on a 25 DegC day, the radiator output would be warm enough to let the PRRT open and function ok, all the time??

 

[SLR No.77]

Quoting Rob Walker: 

If you are seeing 97c then the stat should be well open and water should be circulating around the rad. If it is not then the system could be airlocked or the stat is faulty and the emerald is sensing circulated coolant in the bye pass loop only.

 

Rob

 

Edited by - Rob Walker on 4 Mar 2013 10:25:18

Surely the Emerald can only ever sense circulated coolant in the bypass loop for this setup

I have my fan controlled by the Emerald and I've never been altogether satisfied with it. It gives the ability to adjust the on/off temperature but as an install maybe the location of the sender is simply not correct for the job I'm demanding of it? I'm not aware there's the ability to have another (3rd) temperature input into the Emerald but reading the temperature at the radiator would appear to make more sense for fan control.

 

Stu.

[skydragon]

Totally agree Stu. It may be a case of trying to control the raditor fan, which should be actuated ideally by the temperature of the coolant at the top of the radiator, by using a temp sensor in the water rail is not a good idea. The solution is easy, by using the standard radiator thermostat switch instead to control the fan (although it would have been nice to be able to program on/off points).

 

The more worrying issue is why the PRRT doesn't seem to work properly as a thermostat unless the radiator has warmed through first, causing an initial rise in temperatures when first stopping. This isn't causing any harm and mayby I should ignore it, but I'd prefer it to work correctly if possible.