IPD sale Volvo Parts
Did you know? 🤔
Logged in users can get email notification of topic replies Log in or register (free).
Amazon Link Buy your stuff using this and it helps MVS!

1999 V70 Radiator Fan only runs when AC is on

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.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70
abskee
Posts: 2
Joined: Thu Mar 07, 2019 10:57 am
Year and Model: 1999 V70
Location: San Francisco
Has thanked: 0
Been thanked: 0
United States of America
abskee

1999 V70 Radiator Fan only runs when AC is on

Post by abskee » Thu Mar 07, 2019 11:09 am

My car has started overheating in stop and go traffic, especially if I'm driving on the freeway and then come to a stop for a few minutes. I assumed it was just a bad radiator fan or relay, but if I turn on the AC the radiator fan comes on as expected (it turns on maybe a minute after the AC compressor kicks in). The relay checks out too, I have 80k-ohms between either input pin and ground, and grounding the input pins on the relay turns the fan on both high and low speed. The temperature sensor also seems fine, I replaced it a few years ago (it had failed, so the fan was always on), but I get reasonable readings on from the engine temp gauge on the dash and from the OBD scan tool. Any ideas on what's going on? Does anyone know at what temperature the fan should turn on?

To recap:
  • Radiator fan never turns on due to heat. The radiator just boils eventually.
  • Fan turns on when the AC is on, so the fans, relay, and wiring seem fine.
  • I do get data from the engine temp sensor, and it seems reasonable, although I haven't pulled it out to test the accuracy yet.



User avatar
abscate
MVS Moderator
Posts: 16595
Joined: Sun Feb 17, 2013 5:54 pm
Year and Model: 99T5 ,99S70,2005V70
Location: NYC, ALBANY NY
Has thanked: 157 times
Been thanked: 477 times
Trinidad & Tobago
abscate

Re: 1999 V70 Radiator Fan only runs when AC is on

Post by abscate » Thu Mar 07, 2019 11:41 am

I did a series of observations in stop and go and got fan on at 105C and off at 87 C


1 SWMBO for 30 years
2 Volvos
3 VWs
4 Careers
5 cats/dogs/gears
6 Perfect Ladies in waiting
7 Drivers
8 Boats- with a big pointy metal thing on top

1999 V70 T5M 56 2005 V70 NA M56 VWs BMW

Chuck W
Posts: 121
Joined: Wed Dec 24, 2014 10:45 am
Year and Model: 97 854 T5
Location: Indianapolis, IN
Has thanked: 3 times
Been thanked: 8 times
United States of America
Chuck W

Re: 1999 V70 Radiator Fan only runs when AC is on

Post by Chuck W » Thu Mar 07, 2019 12:44 pm

Have you checked that ECT connector for corrosion? How about the relay input connector?

Could be bad wiring from the ECU to the fan relay.



abskee
Posts: 2
Joined: Thu Mar 07, 2019 10:57 am
Year and Model: 1999 V70
Location: San Francisco
Has thanked: 0
Been thanked: 0
United States of America
abskee

Re: 1999 V70 Radiator Fan only runs when AC is on

Post by abskee » Thu Mar 07, 2019 3:23 pm

Okay, dove into it a little more, I'm thinking my temp sensor is reading low enough to cause trouble, but just not low enough that I noticed an issue.

I unplugged the temp sensor and put a 150-ohm resistor across the contacts that go to the ECU The car turned the fans right on and the engine temp read 250 degrees F, which is about right for that resistance in a working temp sensor, so it seems like the ECU is reading and turning the fans on fine.

I ran the car until it overheated and the coolant starts boiling when the engine is reading like 180F, with the dashboard gauge just above 3 o'clock. So either water has failed and started boiling at 180F, or my engine temp sensor failed and it's reading like 50 degrees low. I tried cleaning the connectors at the sensor, no difference, so it's got to be that sensor. I've just never seen one fail and be a little low, they seem to always be completely shot.

I'm gonna swap the sensor out with a proper Volvo one this time and see how it goes. I'll report back.



loveMy850
Posts: 171
Joined: Sun Oct 08, 2006 2:55 pm
Year and Model: 1994 850 WAGON
Location: California
Has thanked: 12 times
Been thanked: 0
United States of America
loveMy850

Re: 1999 V70 Radiator Fan only runs when AC is on

Post by loveMy850 » Fri Mar 08, 2019 3:41 am

That's pretty much the norm on the volvo. they don't need a whole lot of fan.



User avatar
abscate
MVS Moderator
Posts: 16595
Joined: Sun Feb 17, 2013 5:54 pm
Year and Model: 99T5 ,99S70,2005V70
Location: NYC, ALBANY NY
Has thanked: 157 times
Been thanked: 477 times
Trinidad & Tobago
abscate

Re: 1999 V70 Radiator Fan only runs when AC is on

Post by abscate » Fri Mar 08, 2019 3:55 am

abskee wrote:
Thu Mar 07, 2019 3:23 pm
Okay, dove into it a little more, I'm thinking my temp sensor is reading low enough to cause trouble, but just not low enough that I noticed an issue.

I unplugged the temp sensor and put a 150-ohm resistor across the contacts that go to the ECU The car turned the fans right on and the engine temp read 250 degrees F, which is about right for that resistance in a working temp sensor, so it seems like the ECU is reading and turning the fans on fine.

I ran the car until it overheated and the coolant starts boiling when the engine is reading like 180F, with the dashboard gauge just above 3 o'clock. So either water has failed and started boiling at 180F, or my engine temp sensor failed and it's reading like 50 degrees low. I tried cleaning the connectors at the sensor, no difference, so it's got to be that sensor. I've just never seen one fail and be a little low, they seem to always be completely shot.

I'm gonna swap the sensor out with a proper Volvo one this time and see how it goes. I'll report back.
x

If you used a cheap aftermarket part first time, this is probably the cause.

The resistance vs temperature chart for the 1999 ME7 cars is logged in my T5 maintenance record if you can't find it here in this forum. It is paginated a bit funny, the columns need to be shifted over one notch , so look it over and ask questions here


1 SWMBO for 30 years
2 Volvos
3 VWs
4 Careers
5 cats/dogs/gears
6 Perfect Ladies in waiting
7 Drivers
8 Boats- with a big pointy metal thing on top

1999 V70 T5M 56 2005 V70 NA M56 VWs BMW

Post Reply