Volvo RWD 700 Forum

I replaced the temperature sensor that screws in the side of the block 2 years ago. I noticed driving it today, the needle sits about mid way as usual, but sometimes when slowing down or idling it drops to about (if it were a clock face, mid way is about 1200) to about 1045 and jiggles between there and 1200, sometimes dipping to about 1000. It does not quit working, and it stays steady at 1200 most of the time.

Thoughts on a fix or don't worry this is normal..\\?
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

and I'm gonnna snag a water temp gauge off an old 900 series. Will post results.
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

Before you tear things apart, have a look at this excerpt from the FAQ - aptly titled "Temperature gauge fluctuates".

http://www.brickboard.com/FAQ/700-900/ElectricalInstruments.htm#TemperatureGaugeFluctuates

I'm inclined to think that it would take a shaky thermostat indeed to cause fluctuations in temperature indication - at least I've never seen it. However, back in my '78 264 days, I had a radiator job done (self-diagnosed) when the problem turned out to be the voltage stabilizer on the back side of a "Rally Dash". Follow up on the electrics first, if it's an odd indication.

Good luck.

Garth

Your thermostat may be ready to die.
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Post Back. That's whats makes this forum work.

Let's see what that does for the jiggly needle.
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

I changed it out last night, test drive, still jiggles. Works, but jiggles.
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

so, do I need to replace the thermostat? that is easy enough to do. how does this make the needle jiggle like that?
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

It's opening and closing not properly so bad readings. I would try loosen/tighten the sensor. Sometimes the ground is bad.
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Post Back. That's whats makes this forum work.

Is there an air bubble in the system? Is your coolant low?

Ari

I have a 2 wire connector to the coolant sensor in the block by the knock sensor. Is there any way to test to see if it is working propery by using my ohmmeter?

Is there a way to test the thermostat in any way except by opening her up and looking for a broken arm?
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

coolant is not low
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93' 240 Classic Wagon 220K & 92' 740 Wagon Regina/Rex 90K

I have a 1990 740 GL regina and my needle is starting to have trouble staying up to temperature. In fact, it barely gets warm on a cooler day, but always makes it to temperature in traffic, but drops down some when get on the highway.

I ordered a thermostat and the sensor because earlier this year the on board computer said the ECT was bad, so you may have solved yours already

- if you did, please let us know what the problem was.

As a side note, does anyone know if someone squeezes the upper radiator hose to the thermostat, could it make the temp. gauge do this by putting either air in the system or something.
I don't really know, but I remember someone did that when we were just taking look under the hood, I could have nearly hit them b/c I don't like people squeeze, pulling, and pushing on things under the hood with almost 300k miles and a lot of original stuff. Afterward (the next time I drove the car), it has been operating like I describe since. 10 miles of 45mph-65mph driving to work and barely makes it to temperature. It's been in the 70-90s, barely 70 in the morning.
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1990 740 GL 293.2k miles