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Coolant Light Wont Go Off

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

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Coolant Light Wont Go Off

Post by kory » Mon Sep 16, 2019 1:43 pm

Hey y'all, first post here.

I've got a 2000 S70 GLT with 177k miles

A few weeks ago I had my oil changed at a Take 5 chain, where I also let them do a coolant flush. My coolant level light came on while they were sucking it all out, which is to be expected, but as they were filling it back up the light went off and then on again. Shy me didnt bother asking them about it at the time and I drove off. I checked my coolant level constantly for a few days as the light stayed on, the level was really high and didnt go down after driving around short trips for a few days. I took it back in a week later for them to have a look. They showed me where the floater in the coolant expansion tank was off the post and floating way up at the top of the coolant. They lowered the level to in between the min-max markings and sent me back on my way. The light still never went off so, I ordered myself a new tank (uro) with a new sensor (volvo) and cap (uro i think) while I was at it. Yesterday I switched all these new parts in myself. I've done the tank before after I got the car 10k miles ago because it was cracked at the bottom, easy job.

Anyway, after all the new parts are in and the coolant was refilled, I started up the car and the light was off, good! So I warmed it up, drove it around the block for a few minutes, got it up to temperature and hit the highway. I floored it on the on ramp, when my rpms got up to 6500 or whatever and switched gears, I heard a quick sound in the engine, I dont remember it well enough to describe but it was concerning, and the coolant light flicked on. I thought I blew a hose or something because I thought I heard something flopping around under the hood. I got over as quick as I could and watched the engine temp which didnt budge from the normal middle position. When I looked under the hood, everything looked fine. Didnt see any busted hoses or leaking or anything. Coolant level was normal. I got it home fine, car will still running normal, and left it parked until I looked again today, just to make sure all the hoses I reconnected were tight, sensor was plugged in all the way, inside of the tank looks fine, floater is in position. But the dang coolant light is still on.

Where should I look next for solving this one?

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Re: Coolant Light Wont Go Off

Post by abscate » Mon Sep 16, 2019 1:58 pm

The cooling sensor is a normally open sensor, and is closed magnetically when the coolant level is right.

Terminal 2 on the sensor BN SB shares voltage with terminal 1 on the high pressure AC pressostat so you can check voltages there as a diagnostics (or wait for erik to post swap in a spare sensor he is busy counting cells today so Im covering for him)
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