Coolant Temperature Gauge Sender

[Forrest]

The coolant temperature gauge on my 1997 940 has stopped working. I am 99% certain it is the sender at fault. I have removed the connector and tried shorting the two contacts and the gauge then swings fully to the right when the ignition is turned to position 2. In normal operation the needle doesn't move at all.

I have got a new sender and, for good measure, inlet manifold gasket on order from FRF Motors. However, I am quite keen to change the sender without having to pull the inlet manifold. It is the front, more accessible, of the two coolant sensors. My own skills are more electrical than mechanical.

Any tips on getting the old sensor out without wrecking anything or rounding off the brass hex nut? Are there any specialist sensor wrenches on the market that might improve my chance of success?

[CTCNetwork]

Hi,

If I remember correctly the front sensor is for the gauge and the rear sensor is for the ECU.

Given it is measuring the coolant you'll need to drain, even partially some of your coolant out so you can remove the sensor and fit the new one.. You'll find a drain **** in the lowest pipe under the engine. Fit a pipe, drain into a 5 ltr can and then tighten up and start from there.

Des. . .

[bob12]

Attached is diagram of the head sensors that someone sent me some years ago. Bob.

[Ian21401]

The coolant sensors on my 2.0L petrol '92 940. The one nearest the front of the engine is the one connected to the temperature gauge. It has two wires, yellow/black and white/yellow. I don't think it's possible to remove it without removing the intake manifold as the sensor body prevents use of a ring spanner or socket and there is insufficient space to use an open end spanner.

[bob12]

Originally Posted by Ian21401

The coolant sensors on my 2.0L petrol '92 940. The one nearest the front of the engine is the one connected to the temperature gauge. It has two wires, yellow/black and white/yellow. I don't think it's possible to remove it without removing the intake manifold as the sensor body prevents use of a ring spanner or socket and there is insufficient space to use an open end spanner.

It is possible to remove the temp sender without touching the intake manifold ... but it is not an easy task..

[Forrest]

Well, the parts arrived today so when I have a bit of time I'll have a go at it. I am inclined to have a go without removing the intake. I think if I had an open spanner with an offset (like a ring spanner) it would be quite easy, but without the offset it looks as though the block will get in the way.

I've read elsewhere that some people advise breaking off the plastic around the electrical contacts and using a long socket. However, I never like irreversible steps in a job like this.

I've been looking at O2 sensor wrenches and various open ratchet spanners on-line wondering if any would be suitable. I might take the new sensor into Machine Mart and see if they have anything fits it.

Anyone know if it's likely to be easier to loosen the sensor when it's hot or cold? And yes, I do know it would not be a good idea to take it right out when the engine is hot!

[Forrest]

I managed to swap the sensor today in less than half an hour without removing the inlet manifold.

The secret to doing it seems to be:

1) Remove the knock sensor. I now know that this really needs re-tightening to the correct torque, but my torque wrench is not accurate below 10lb·ft so I just nipped it into place with a 1/4" socket. The engine seems to run fine.

2) Remove the little plastic wire holder pictured below. It just lifts out of the way.

3) Use an open spanner long enough to get enough torque and short enough to fit the gap. I found my decent quality 19mm spanner too long, but one out of a really cheap set worked a treat.

Coolant temperature gauge is now working again!



Small wire holder best moved out of the way.



The long spanner above was too big. The cheap one below was just right.



The old sensor removed undamaged.



The new sensor in position with the knock sensor still removed. No sealing compound, just a tiny trace of copper grease on the thread to aid future removal. Volvo part number is 1362645.

[baggy798]

When I tried to remove mine the open end didn't fit on the hex flats in any position, so I had to break the plastic D part so the ring end could get past it. I made a hash of it, but I got it out eventually.

[bob12]

Excellent Forrest, glad u got it done and the pics are useful for those wanting to change the sensor without Baggy 798's 'little' difficulty' ........ now I remember the way to do it. My difficulty factor came from loss of memory.

[Diesel-do-nicely]

i bought a cheap ring spanner, with a grinder, shortened it and cut a slot on the ring to fit past the shield above the pins.
using the open end spanner can round of the sensor , if its in tight.

tada , one volvo special tool........