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Overheating at idle 850

posted by rice240 on Wed Sep 21 11:36 CST 2022
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last visit: Tue Aug 26 10:51 CST 2014

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Hello, My 1994 850 Turbo is overheating at idle. I hear the fan coming on most of the time, but it might be intermittent. I know because the AC stops and then eventually the gauge will go up. When I drive, it all goes back to normal.

Here are my questions:

1. Is there more than one temp sensor (besides the one on the thermo housing). Does that tell the aux fan when to come on?

2. Could a failing thermostat be causing this?

3. Could a failing water pump give these symptoms?

4. Lastly, if I wanted to rig up a light to come on in the cabin when the aux fan comes on, where would you guys tap into the system. I am wondering if the it isn't coming on properly.

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Overheating at idle 850

posted by jwalker on Thu Sep 22 06:15 CST 2022
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last visit: Fri Jun 6 08:39 CST 2014

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Is it your original radiator? Maybe second radiator? Had a similar issue with my high mileage 240 with its original radiator. The tubes in the core clog with age and the radiator loses cooling efficiency. If the new thermostat doesn’t work consider thoroughly flushing the radiator to see if that improves the situation. If that doesn’t work it is replacement time. 28 years is a very long life for a radiator….😊
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Will I buy another Volvo??? We'll see....

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Overheating at idle 850

posted by rice240 on Thu Sep 22 12:24 CST 2022
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Smart, but I already replaced it because it was leaking. It was my sister's car and she was going to use it as a trade in and they only offered $500.00. I couldn't stand it. I work on my old 240 so I decided to fix it up. I've already spent way too much on it to stop now!

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Overheating at idle 850

posted by jwalker on Thu Sep 22 13:57 CST 2022
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"It was my sister's car and she was going to use it as a trade in and they only offered $500.00. I couldn't stand it. I work on my old 240 so I decided to fix it up. I've already spent way too much on it to stop now!"

Ah-ha - A typical old Volvo owner's story! They suck you in!

1. You may have a funky temp sensor. Good idea to replace it with the thermostat. AFAIK there is only one temp sensor.

3. Doesn't sound like a water pump issue.

BTW - Besides the 90 240, I owned a 95 and a 93 850. Drove the 90 240 and 95 850 for a long time. I replaced the radiator on the 95 and the 93 needed one when I sold it. Both leaked. The factory radiator on the 240 was still going at 300k. Running hot at stoplights but still going...:)

94 turbos are pretty quick, yes?

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Will I buy another Volvo??? We'll see....

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Overheating at idle 850

posted by rice240 on Fri Sep 23 11:21 CST 2022
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last visit: Tue Aug 26 10:51 CST 2014

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Thank you for the replay. Yes, the Turbo is fun and very quick, especially mind-blowing after driving my 240! But the 240 has a M47 and in the winter (with the AC off) it is fun. I have a VX Cam in it and the Turbo Exhaust, it will scoot around pretty good.

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ECT resistance chart 850

posted by B.B. on Fri Sep 23 07:23 CST 2022
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last visit: Mon Oct 6 13:15 CST 2014

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Check the ECT with your VOM

COOLANT TEMPERATURE SENSOR RESISTANCE TABLE (850 turbo)

Temperature -
F ( C)
Ohms
32 (0) .............................................. 7300
68 (20) ............................................. 2800
176 (80) ............................................. 300
212 (100) ............................................ 150

Resolve overheating problems ASAP, so you don't wind up with more serious issues.

Good luck, Bill

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ECT resistance chart 850

posted by rice240 on Fri Sep 23 11:22 CST 2022
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Oh that is great info. I need to get better with my multimeter. I am afraid of it!

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ECT resistance chart 850

posted by B.B. on Fri Sep 23 13:38 CST 2022
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last visit: Mon Oct 6 13:15 CST 2014

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The VOM is simple to use and not to be afraid of. When measuring high voltages
just keep your fingers on the probes and NOT on the high voltage.

You are reading Ohms to check the sensor, the symbol looks a little like a horse shoe.
Put one probe on each sensor wire and see what the resistance is on your meter.
Compare hot and cold resistance readings with the chart to check the sensor.

There's a pile of tutorial videos on line to help you get up to speed quickly with your VOM.

Just do it, it's easy.

Bill

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ECT resistance chart 850

posted by jwalker on Fri Sep 23 11:54 CST 2022
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last visit: Fri Jun 6 08:39 CST 2014

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I'm not good with electronics either. While getting up to speed with your meter you could visually check the condition of the wiring to the sensor. Particularly the connection at the sensor. 28 years of Texas heat might have damaged it!
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Will I buy another Volvo??? We'll see....

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Overheating at idle 850

posted by rice240 on Thu Sep 22 12:18 CST 2022
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Overheating at idle 850

posted by B.B. on Wed Sep 21 19:19 CST 2022
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last visit: Mon Oct 6 13:15 CST 2014

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My first guess, maybe the thermostat is stuck?
I'd suggest soaking the thermostat mounting bolts with mystery oil for
a few days before attempting to remove. They have a bad reputation for being stubborn to remove. Some long soak with MMO can make it easier.
Replace with an OEM quality thermostat and do use never-seez on all steel bolts going into aluminum on reassembly
Retap borked threads as needed.

Bill

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Overheating at idle 850

posted by rice240 on Wed Sep 21 20:03 CST 2022
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last visit: Tue Aug 26 10:51 CST 2014

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Thanks for the reply. I went and sprayed them at your suggestion with PB Blaster. Ordered a Genuine Volvo thermostat, temp sender and new bolts from FCP. I’ll soak them daily until it arrives. So if it gets too hot, I’ll lose coolant out of the cap I suppose? Temp seems fine while cruising. If I hit a light it creeps up. Plus it was in the high 90’s today here in Texas.

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