Unfortunately the one question I had just turned into two. Here's the first. I just finished crafting a well written question to my brick buddies regarding my faulting engine indicator. I was proof reading before submitting and my hand brushed casually onto the key board of my lap top and the question just disappeared. This happens on approximately 50 percent of the questions I write before I have a chance to submit them. You can imagine how aggravating it is to have this happen. Its like to bad old days 20 years ago when no one really understood how to save files to floppy disks and sometimes you'd just loose your work. Does this happen to anyone else.

OK. Here's my question, again.

For a while the temp indicator has been intermittent and I can't attach this inconsistency to anything particular like rain, or low coolant. Lately the intermittency has stopped and the indicator just doesn't work.

I've read the maintenance section on this problem and the recommendation involves a fairly demanding job including removal of the intake manifold, which I haven't done before, but probably can.

Before I get into something that difficult, is there something simpler I should try. Too often, I've gotten into difficult or two much work by failing to ask the right question and missing something obvious.

If I have to remove the sensor from the engine, I will. I happen to have a spare temp dial indicator, but usually is not the instrument in the dashboard, is it?

Bob Franklin
'94T, 95T & 95 940 Wagons

There are two temp sensors-- one close to the front of the motor that is for the gauge, the second is the one that is buried behind the intake manifold. That one is for the fuel injection computer.

If the first is bad you'd have troubles with the gauge. If the second is bad, you'd have trouble with how the car runs.

Good luck!

Dear robertmfranklin,

Hope you're well. If the temperature gauge in the instrument cluster is not working, replacing the sensor does not require removal of the manifold. That sensor is next to the knock sensor, i.e., towards the front of the head, on the driver's side (North American models). You probably will need to remove the idle air control motor, which is affixed to a bracket, with two 10mm bolts (if I recall correctly). Removing the IACV requires loosening two hose clamps. The wiring connector can be left.

Once you can reach the sensor, compress the electrical connector release and wiggle the connector, gently, from the sensor. You can then use an open-end wrench to remove the sensor. There's no need to drain coolant: perhaps a tablespoon of coolant will dribble out. Put in the new sensor, and tighten gently with the wrench.

When you re-seat the electrical connector on the sensor, be sure the tubular metal contacts, that slide over the sensor's tubular "pins" actually do slide onto the pins. If the housing has deteriorated, you may need to seat each wire's contacts onto its pin.

If the engine coolant temperature sensor - which sends a signal to the Engine control Unit (ECU) - needs to be removed, then the intake manifold will need to be removed. There should be a diagnostic code on Port A2. The code is 1-2-3.

Please post back with any codes.

Hope this helps.

Yours faithfully,

Spook

Generally agree with Spook, except that I replaced my ECU temp sensor without removing the manifold. Not terrible, does lose coolant unless some is relieved.

I've read Spook's procedure for replacing the sensor. As soon as there is a warm day, I'll try to do it. Meanwhile, at a minimum, I will try locating the unit in the head and perhaps jiggling the electrical connection will put some life back into the Temp gauge at the instrument panel.

Spook you refer to a "knock" sensor in the same area as the engine temp sensor. What is a knock sensor?

[As for the lukewarm heat coming from the vents, I tried your procedure of burping the coolant, but no success. Other ideas]

Bob Franklin

Thank you to all and particularly Spook for the very clear and helpful explanation of how to remove the engine temp sensor. The warm day I was waiting for finally came this weekend (Boston). I was able to locate the sensor and with minor difficulty remove it without moving any other component. On my 1995 940 Turbo it was accessible with a 17 mm open end wrench - just barely. My wrench was a rather short length as it came out of my BMW OEM tool kit, so I would recommend something a little more like 12 to 14 inches so you have some leverage. The sensor comes out easily because its brass in the iron.

I called my local Volvo dealer and they had the replacement for $66. I purchased one on line for $14 and $5 shipping. It should arrive this week and I'll update on the success I am anticipating.

Bob Franklin

A couple of important corrections:

I mentioned a 17 mm open end wrench to remove the engine temp sensor. That was wrong. It is 19mm.

I thought I was so clever to purchase from Pelican Parts the same sensor @ $14 offered by Volvo @$66. It arrived yesterday but when I went to screw it into the engine it turned out the threads were about 2/3 the diameter of the original. So I have to arrange to send it back and then wonder if another replacement will work.

Otherwise the probe and electrical connection appeared to be identical.

Bob Franklin

I forgot to mention, I put an Ohm meter on the temp sensor after I removed it and got infinite resistance. I just received the $14 replacement at my door 2 PM Monday. Ordered it Friday PM. Not bad. Ohm meter indicates a resistance of 4+ Ohms so I know its doing something the old one wasn't.

Bob Franklin

What year is your car? On our 1994 940, the resistance of the temperature gauge sender is about 2500ohms with a cold engine, and about 200ohms fully warmed up.

If your new sender really is showing 4 ohms at room temperature I would think it is faulty. Did you mean 4k ohms?

BTW, these gauges have some kind of compensating circuitry in them to dampen out needle movement once the engine is warmed up - ie: minor temperature fluctuations do not move the needle. I observed the sender resistance varying considerably when comparing normal speed to idling in traffic with my multimeter connected to the sender terminals, but duplicating the driving conditions later, the gauge needle never moved from the 12:00 spot.
--
Bob: son's 81-GL, dtr's '94-940, my 83-DL, 89-745(V8) and 98-S90. Also 77-MGB and some old motorcycles.