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What is causing my cooling fan to run for no reason?

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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98V70T5
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Year and Model: V70 T5 1998
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What is causing my cooling fan to run for no reason?

Post by 98V70T5 »

Hello,

I have a 1998 V70 T5. Absolutely love the car!

When I drive, I notice at random times, my coolant gauge will drop to the bottom, and my radiator fan will come on, at full power. This can happen even when the outside temp is 0F (I live in a very cold place), so it's not just occurring during the summer. The fan will remain on, even with the key off, and the car locked! One day, when I first noticed it, I was lucky to catch the problem, so I just unplugged the radiator fan connector, to save the battery!

The only way I figured out how to "reset" this condition, is to turn the car off, wait about a minute, the fan is still running during this time, then restart the car. After about 3 minutes or so, the fan will turn off, and I can continue to drive, or park the car without worrying about it draining my battery. Whenever I see my coolant gauge drop to zero, I know the condition is happening, so I will pull over, and reset the car. This is getting annoying, and I would like it fixed.

Can anyone lend insight into this problem?
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chrafael
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Re: What is causing my cooling fan to run for no reason?

Post by chrafael »

First and easiest thing to check is the coolant temp sensor and connector by the thermostat housing. I'm sure there's a chart somewhere in the Volvo Repair Database that shows what the resistance should be at various temps.
98V70T5
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Year and Model: V70 T5 1998
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Re: What is causing my cooling fan to run for no reason?

Post by 98V70T5 »

What explains why the fan runs with the key off, and the car locked? I know my friend's old VW would run the fan with the car off and locked, but it would time out after 2 or 3 mins. Mine will run until the batter dies.
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Re: What is causing my cooling fan to run for no reason?

Post by scot850 »

+1 on checking the temp sensor and the connector that mounts onto the power steering pump. Sensors have a lifetime, and I only use Volvo part although I know others have recommended an aftermarket brand, I don't recall the name. The fan relay could also be faulty (sits above the radiator). Your fan works so that is good.

The fan can run for a short time after the ignition is switched off, to reduce the engine bay temperature from suddenly spiking when the car is switched off. That is normal. I always found my turbos do this more than the NA as they get hotter under the hood.

Start with the temp sensor and connector first. There are resistance charts for various temperatures on the internet and I know I posted a link to them a few months ago.
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sleddriver
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Re: What is causing my cooling fan to run for no reason?

Post by sleddriver »

A defective ECT sensor will cause this. So will an open ECT connector. So you could install a brand new ECT and the problem would still remain. Thus, check the connector first. Been there, done that: Big Sled Thread
1998 V70 T5 226,808 miles. Original Owner.
M1 10W-30 HM
98V70T5
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Year and Model: V70 T5 1998
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Re: What is causing my cooling fan to run for no reason?

Post by 98V70T5 »

sleddriver wrote:A defective ECT sensor will cause this. So will an open ECT connector. So you could install a brand new ECT and the problem would still remain. Thus, check the connector first. Been there, done that: Big Sled Thread
I just read your fix, on your Sled. It makes sense now, why the coolant fan could be running, all the time, or randomly. I am going to check the connector. I'd imagine there is an issue with it. I'd even venture a guess my sensor is fine, and it's just the connection!

I also remember now, the engine runs really rough, during this episode, leading me to believe its getting a MAX reading from the sensor.


I appreciate your reply!
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Re: What is causing my cooling fan to run for no reason?

Post by polskamafia mjl »

This happened to me after my manual swap. After putting the engine back in and reconnecting the wiring harness I noticed the cooling fan ran all of the time and after shutting the engine off the fan continued to run for a while.

It turned out that the plug for the ECT sensor was damaged causing the ECU not to get any kind of signal from the ECT sensor. It seems that the fail safe then is to have the fan run all of the time and to continue running once the engine is turned off. Once I repaired the wiring the fan started working normally.

Check your wiring and replace the sensor as required but use an OEM one.
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98V70T5
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Year and Model: V70 T5 1998
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Re: What is causing my cooling fan to run for no reason?

Post by 98V70T5 »

Any tips or links to purchasing a new connector, or connector + pig tails? I'm just going to order it, anticipating this is the problem. Thanks!
98V70T5
Posts: 83
Joined: Tue Nov 02, 2010 9:45 pm
Year and Model: V70 T5 1998
Location: I wish it was Sweden

Re: What is causing my cooling fan to run for no reason?

Post by 98V70T5 »

QUICK UPDATE:

I have done some testing, and came up with a pattern of when the fan locks into high mode. Perhaps those in the know, will be able to help me pin point the correct route to take, in diagnosing and buying parts.

Observation 1: Starting the car up from cold, and letting it run for up to two hours at idle, the low speed fan cycles on and off, at temperature, and never locks "on". I've even turned the car off, just as the fan kicks on, and the fan will turn off.

Observation 2: Starting the car up from cold, with the AC ON, the first time the fan kicks on (it defaults to high speed mode) high speed, it locks into high speed mode, and won't turn off. It takes a few mins, after turning the AC on for the fan to kick on. The fan DOES NOT instantly go into high speed mode, the moment you turn the AC on. There is a period of time, perhpas 10mins before I hear the fan turn on at all. Turning off the AC does not turn the high speed fan off. The only way to get the fan to turn off, is to turn the key off, remove key, insert key, turn to ON, turn off the AC, then start the car.

Once the car starts, the temp gauge reads full cold, even though it was at normal operating temp just PRIOR to turning the car off, and the fan will run on high speed for about 3 minutes, then TURN ITSELF off, and all is good, UNLESS I turn the AC on, then the fan behaves as described above, locking into high speed mode. Keep in mind, where I live, it's 25F right now.

Do these observations help narrow the problem down? I pulled a used fan relay from the yard, but haven't installed it yet.

Thanks everyone!
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Re: What is causing my cooling fan to run for no reason?

Post by sleddriver »

?????
Have you tried the fixes suggested earlier?
Results?
I'm surprised your AC would engage if it's 25F outside.....
1998 V70 T5 226,808 miles. Original Owner.
M1 10W-30 HM
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