Hello,

You may remember over the holidays driving from SF to SD and back I had some weird issues with my temp gauge randomly going up to 3/4 sometimes, then coming down to half or just below half on its own- https://volvoforums.com/forum/volvo-...freeway-75636/

I usually just drive the car around town and noticed it here and there, but it hasn't been a big deal, always goes back to the middle, never into the red. Coolant is only a couple months old i did a flush. The other day the temp gauge just quit altogether. The gas gauge still works btw.

Does this mean the cooling system isn't working at all and it's unsafe to drive the car?

I'll check that the sensor beneath the intake is in tact and the wire okay. Other than that, I have no clue what to do. New thermostat? New sensor? Remove the instrument cluster and check something?

Thank you.

 

Have you checked the gauge? Disconnect the wire on the sensor and attach it to earth. The gauge should be at max. If still nothing, check the sensor wire with a multimeter to see if your getting continuity.

I had a problem with temp sensor and it was down to corrosion on the spade connector. I used emery cloth on the sensor connector and slide the wiring connector on a off a few times which cleaned the corrosion off. Works now.

You said you did a coolant change, did you have this fluctuating temperature problem before?


Dan

 

Do you have to cut it and re-solder or is there a connector right on the sensor?

If it maxes, then what?

 

If it max'd out then the gauge is fine. You can check the sensor by check resistance on the sensor, it shouldn't be 1... 0.6 or something like that. If that checks out ok, clean up the connector on the sensor with emery cloth/sandpaper. Then slide the connector on and off a few times. You can then check continuity at the wiring connector to make sure its making contact.

The wire going to the sensor is a spade type connector

Dan

 

So if you connect the sensor wire to ground and it maxes but you can't get it to work with it attached to the sensor, then the sensor needs to be replaced?

What if the wire doesn't go to max? Then the wiring is bad?

 

If you earth the sensor wire and the gauge goes right to the top then the gauge and wiring is good. If it doesn't do this, check the wiring at the connector (under the plastic cover) as it could be as simple as corrosion. If this is ok then the wiring or gauge is bad which will need further investigation.

Clean up the spade connector on the sensor make sure there is no corrosion. If you use a multimeter on the sensor it should be 0.6 or somewhere around there when the engine is cold. If your getting no continuity then the sensor is bad

My money is on corrosion on the sensor or the connector or both.

Did you have this fluctuating temperature issue before your coolant change? I have seen airlocks cause fluctuating temperatures, as the air moves around the system it gets stuck in the pump which doesn't allow the movement of coolant thus increasing the temperature. It finally gets past the pump, then the coolant starts to move which lowers the temperature. Are you getting constant hot air from the heater in the car?

Dan

 

Hello,

Thanks for the advice.

Before I changed the coolant, I would cold-start the car and one out of every 5 or so cold starts the gauge would start to go up, and go STRAIGHT to the top, like, within a block, and then come down to center. I'd never experienced anything on the freeway like I did on the way to San Diego. Anyways I changed it, closely following all the rules in my Haynes manual as well as advice of folks on this board... running water through till it's clear, letting it idle for 30 seconds with water in it, running more water through, putting coolant in, running for a few minutes with reservoir cap off, squeezing top radiator hose to expel air, etc. Heater is hot, all the time. I don't think it's air trapped in the system. I'll check wiring when I get home if it's not still raining too much.

I still haven't heard whether any of this means it's unsafe to drive the car. Is coolant still moving through the system even if the gauge doesn't work? I'd like to know because it's supposed to rain for the next 5-6 days.

Thanks!

 

its possible you have a thermostat thats sticking closed, but finally opens..

 

I don't see why you'd get an air lock with the procedure you have described.

As pierce said about the stat, that could be to blame. I'd just replace it to rule it out, they aren't too expensive.

If it was me I wouldn't want to run it until I knew what the problem was. It could be an expensive fix if it is overheating.

Dan

 

I fixed it. Pulled the sensor wire, cleaned it, reattached. Let engine idle with reservoir cap off for a good while, longer than when I changed the coolant. Temp gauge hasn't gone past half in 70 miles. Awesome. Thanks!!

 

Glad it was a simple fix

Dan