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Volvo 940 electric fan wiring.

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Old Apr 25th, 2018, 17:05   #1
Casheye
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Default Volvo 940 electric fan wiring.

So a while ago I had a new radiator installed in my 940. It has an electric fan but the bloke who did the work didn't put the temp sensor in the new radiator.

Best case scenario, he unplugged it and tucked it away somewhere or worst case, he cut it off the threw it away with the old rad...

I've traced the wires from the relay into the bundle that runs up the passenger side of the engine bay. Now, I assume that it runs up around the side, along the top behind the engine and back down the driver side and into the rad where the hole is.

Does anyone know if I'm right and if I am where it comes out on the loom over on the opposite side of the bay from the relay so I can start hunting for the sensor.
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Old Apr 26th, 2018, 16:01   #2
crogthomas
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If it's a standard fan, it's controlled by the engine ECU under the dash, hence the wiring disappearing into the loom.
The bigger issue might be, why do you have a hole in your radiator?
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Old Apr 26th, 2018, 17:06   #3
Rversteeg
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Default Does this help?

Does this help? Part of a late 940 wiring diagram.
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Old Apr 27th, 2018, 01:08   #4
Laird Scooby
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Why do you want to find the sensor? As others have said, it's in the ECU on your car, derived from the engine management temperature sensor (not the same sensor that drives the temperature gauge) and gives a low spped then a high speed output dependent o temperature and alters the fan speed from slow to fast.

The big question is, what is it not doing?
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Old Apr 27th, 2018, 17:55   #5
Casheye
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Quote:
Originally Posted by crogthomas View Post
If it's a standard fan, it's controlled by the engine ECU under the dash, hence the wiring disappearing into the loom.
The bigger issue might be, why do you have a hole in your radiator?
I don't have a hole in it. But there is a light coloured plastic bung in a hole in the top left hand side (if standing in front of the car) where I assumed the temp sender is meant to go.

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Originally Posted by Rversteeg View Post
Does this help? Part of a late 940 wiring diagram.
Kinda :P

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Originally Posted by Laird Scooby View Post
Why do you want to find the sensor? As others have said, it's in the ECU on your car, derived from the engine management temperature sensor (not the same sensor that drives the temperature gauge) and gives a low speed then a high speed output dependent on temperature and alters the fan speed from slow to fast.

The big question is, what is it not doing?
So maybe I've been looking at the wrong diagrams for this but basically, the electric fan never comes on. I was expecting to hear it on a low setting the other day when stuck in traffic when we had those particularly hot days. But nothing. Now I just assumed that the temp probe/sender/sensor that is connected to that relay was meant to be in the radiator. But I'm wrong? If it isn't, where is it?
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Old Apr 27th, 2018, 18:04   #6
Laird Scooby
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Quote:
Originally Posted by Casheye View Post
the electric fan never comes on. I was expecting to hear it on a low setting the other day when stuck in traffic when we had those particularly hot days. But nothing. Now I just assumed that the temp probe/sender/sensor that is connected to that relay was meant to be in the radiator. But I'm wrong? If it isn't, where is it?
You know the phrase about "assume" don't you?

What position was your temperature gauge in at the time and where does it normally sit once fully warmed up?
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Old Apr 27th, 2018, 18:25   #7
Casheye
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You know the phrase about "assume" don't you?

What position was your temperature gauge in at the time and where does it normally sit once fully warmed up?
The temp gauge sits right in the middle. I don't trust it though because sometimes it'll get stuck at the centre position so when I start the car the next day it'll say it's already warmed up but when I tap on the dash cluster it'll drop back down to the start position.


This is the plastic bung I am talking about.


And THIS is the kind of that I thought went in there?

I distinctly remember there being a sensor like that in my other Volvo.

I know the temp gauge is most likely stabilised so it'll sit in the middle whether or not it's say +/- 10c of whatever is the optimum reading but what is the right coolant temperature?
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Old Apr 27th, 2018, 20:41   #8
Laird Scooby
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Just to clarify, yours is petrol isn't it? It looks like the front end of a B2x0 but the air intake looks a bit odd!

That aside, if your engine temperature drops once it's warm and you're driving at a reasonable motorway sort of speed, you probably wouldn't notice if the gauge is sticky. Not unless you tapped the dash every so often which can do more harm than good at times.

On the basis that it's a petrol engine, the fan should be controlled by the engine management ECU so no need for a radiator mounted fan switch. Older cars that didn't have the ECU control for the fan used a switch in the rad end tanks as your photo shows.

If the temperature drops as above, the fan wouldn't come on as the engine temperature would be too low, even stuck in traffic. I've got rid of the viscous fan on mine and just use the electric fan (switched by a switch in the same position and mainly fitted because of the air-con) and that rarely comes on, even on hot days.
Going back about a month, maybe 6 weeks to the first hot spell we had, i went down to London to collect some bits. Mostly motorway speeds (i mean proper motorway speeds) but i did get stuck on the M25 about tea-time, still very hot outside and even then the fan didn't come on.

As for what temperature, if memory serves correctly you should have an 88C 'stat in yours so it will be a few degrees above that, probably about 95-98C.

Looking at the switch you linked to, it is a 92-87C rating so it comes on when the temperature reaches 92C and stays on until it has dropped to 87C.

As a rule of thumb, the temperature gauge centre line is about 88C (with 90C being just above) and the start of the gauge is usually about 40C with the top of the gauge usually about 130C.
Please note that apart from the central figure these are approximations and could be slightly different depending on make, model and so on. It's more to give you an idea of what should be happening.

Don't forget that although water boils at 100C in normal atmospheric conditions, because the system is pressurised that raises the boiling point considerably. Most of the caps i know of are 1.1bar/16.5psi/1.1 atmosphere roughly speaking.

There are many ways you can measure the temperature of the coolant, i use an infra-red laser thermometer for convenience, was about £8 from Amazon but i had to wait for the "slow boat from China" for it.

https://www.amazon.co.uk/gp/product/B007NVYWUS

Gone up a bit, now £9.99 and i'm sure if you were willing to pay a little more, you'd get one from the UK, either via Amazon or ebay.

https://www.ebay.co.uk/itm/8-Type-No..._tUiSys6JEUJcQ

One from a UK seller on fleabay there for a couple of quid more.

Pointing it at the top hose or the radiator stub the top hose joins onto will give you the most accurate reading.

Comes in handy for checking a lot of other stuff too - fridge, freezer, central heating radiators (identifies easily if they need bleeding), oven - the list is only ended by your imagination really!

If you get bored checking temperatures, you can shine the laser pointer at the ground and get your cat to chase it too!

All said and done, the first thing to do is to verify what temperature the engine is actually running at before you start chasing (potentially) non-existent sensor faults.
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