IPD sale XeMODeX - Experts in Volvo Electronics
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!

Temp gauge fluctuating even after replacing thermostat and CTS

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

Christgen
Posts: 1
Joined: Sat Sep 28, 2019 11:38 am
Year and Model: 1999 S70
Location: Pennsylvania
Has thanked: 0
Been thanked: 0
United States of America
Christgen

Temp gauge fluctuating even after replacing thermostat and CTS

Post by Christgen » Sat Sep 28, 2019 2:58 pm

A few months ago my temp gauge would fluctuate between operating temperature and below, so naturally I checked the thermostat. As I had expected it had broken and was stuck open which explained the drop in temperature. I replaced it with an oem thermostat and decided to replace the coolant temp sensor as well since it was the original. Now about 6 months later the coolant temp gauge is fluctuating again in the same way. I checked the replacement thermostat and it isn't broken. I hooked up a scan tool and the coolant temp does drop when I'm driving from 45 mph and beyond and comes back up to operating temp when stopped, just as it did the first time I had the problem. Any ideas as to what the cause of this could be?



User avatar
misha
Posts: 3977
Joined: Sun Dec 07, 2008 4:09 pm
Year and Model: '97 850 2.5 20v
Location: Serbia
Has thanked: 34 times
Been thanked: 94 times
Serbia
misha

Re: Temp gauge fluctuating at high speeds even after replacing thermostat and CTS

Post by misha » Sat Sep 28, 2019 4:34 pm

Thermostat.
If scan tool confirms drop in temperature on open road just like gauge....it's thermostat.
You can't know if it's bad just by visual inspection.
It can also partially fail....mid way open....not just stuck opened.
Oe & oem thermostats(read quality thermostats) always stuck open avoiding overheating of the engine.


'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS

RB3
Posts: 6
Joined: Sun Sep 29, 2019 4:47 am
Year and Model: 99 V70
Location: California
Has thanked: 0
Been thanked: 0
United States of America
RB3

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by RB3 » Sun Sep 29, 2019 4:55 am

I too am experiencing this as well after replacing the thermostat sensor not long ago. Though I'm not sure it's only at high speeds.



User avatar
erikv11
Posts: 9219
Joined: Sat Jul 25, 2009 2:03 pm
Year and Model: 850, S/V70, 06 S60R
Location: Iowa
Has thanked: 60 times
Been thanked: 202 times
United States of America
erikv11

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by erikv11 » Sun Sep 29, 2019 2:13 pm

To eliminate or pinpoint the thermostat as the issue, remove the stat and drive the car. If it still fluctuates, it wasn't the stat. If it stops, it was.


'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 140k
'98 S70 NA, 210k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 280k
'06 S60 R, 160k
gone: '96 NA 850 210k, '98 NA V70 182k

scot850
Posts: 5531
Joined: Mon Apr 05, 2010 2:46 pm
Year and Model: 2000 V70 R
Location: Calgary, Alberta, Canada
Has thanked: 7 times
Been thanked: 137 times
Canada
scot850

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by scot850 » Sun Sep 29, 2019 4:49 pm

I have found that the P80's are prone to air-locks when playing with the cooling system. These will cause random temp readings.

Try raising and supporting the front of the car, run it up to temperature, and then let the engine cool over night. Although the heating system does have a by-pass it is worth leaving it on hot to help max flow and maybe remove any air. Then see if the problem persists.

The other guys have also mentioned the ways to ID if it is a thermostat issue.

Carefully check the connection to the temp sensor. They are prone to getting fragile with age and can cause intermittent readings.

I think you said you used an OE Volvo temp sensor. If not chances are you will have issues.

Neil.


2000 V70 R - still being an endless PITA
2006 XC70
2003 Toyota 4Runner V8 Limited
2015 Kia Sportage EX-L
1993 850 GLT -Sold
1998 V70 XC - Sold
1997 Volvo 850 SE NA - Went to niece in California - Sold
2000 V70 SE NA - New project and test bed - Sold

User avatar
erikv11
Posts: 9219
Joined: Sat Jul 25, 2009 2:03 pm
Year and Model: 850, S/V70, 06 S60R
Location: Iowa
Has thanked: 60 times
Been thanked: 202 times
United States of America
erikv11

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by erikv11 » Sun Sep 29, 2019 9:31 pm

Typo alert, Neil probably already knows this fact: Actually the heating system does NOT have a bypass. Coolant always runs through the heater core, regardless of engine temp and regardless of where you move the control setting inside the cabin.


'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 140k
'98 S70 NA, 210k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 280k
'06 S60 R, 160k
gone: '96 NA 850 210k, '98 NA V70 182k

User avatar
Eddystone
Posts: 270
Joined: Mon Jan 20, 2014 4:30 pm
Year and Model: 1967 Ford GT40 Mk IV
Location: Philadelphia Metro Area
Has thanked: 14 times
Been thanked: 17 times
United States of America
Eddystone

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by Eddystone » Mon Sep 30, 2019 2:15 am

The air pocket theory sounds most likely to me, but the gauge doesn't really read temperature, but electrical resistance. It is suppose to react to changes in the sensor designed to change resistance as a result of changes in temperature. However, if you have a solder joint on the instrument cluster that has become high resistance or intermittent due to years of heating up and cooling down (on the circuit board) that change at the back of the meter will affect the position of the needle.

I think the troubleshooting advice given above is sound and should be followed. Just pointing out that something a simple as a bad solder joint will cause your meter to fluctuate, as well.


1998 V70 Non-Turbo/Auto
1993 945 Turbo/Auto
1999 S70 T5 Turbo/Auto
All U.S. market models.
All on the road and running.
PM me if you are near Philadelphia.
;-)

User avatar
abscate
MVS Moderator
Posts: 18436
Joined: Sun Feb 17, 2013 5:54 pm
Year and Model: 99T5 ,99S70,2005V70
Location: NYC, ALBANY NY
Has thanked: 211 times
Been thanked: 687 times
Trinidad & Tobago
abscate

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by abscate » Mon Sep 30, 2019 2:42 am

erikv11 wrote:
Sun Sep 29, 2019 2:13 pm
To eliminate or pinpoint the thermostat as the issue, remove the stat and drive the car. If it still fluctuates, it wasn't the stat. If it stops, it was.
That’s a powerful method, controlling all variable but one while manipulating it and monitoring outcome. You should patent that and name it something.


Empty Nester
A Captain in a Sea of Estrogen
1999-V70-T5M56 2005-V70-M56 1999-S70 VW T4 BMW

RB3
Posts: 6
Joined: Sun Sep 29, 2019 4:47 am
Year and Model: 99 V70
Location: California
Has thanked: 0
Been thanked: 0
United States of America
RB3

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by RB3 » Mon Sep 30, 2019 11:03 am

Gonna try this today. Stat and sensor replaced last fall. Not sure if OEM. Also had water pump and timing belt replaced 2 mos. ago so naturally coolant was involved. I haven't noticed any fluctuations since and only topped it once. But after you mentioned the air, I did just run the heat the past couple mornings/evenings.

Been having random electrical issues as well. Replaced battery 2 days ago.

Thanks for tip on Stat.



RB3
Posts: 6
Joined: Sun Sep 29, 2019 4:47 am
Year and Model: 99 V70
Location: California
Has thanked: 0
Been thanked: 0
United States of America
RB3

Re: Temp gauge fluctuating even after replacing thermostat and CTS

Post by RB3 » Wed Oct 02, 2019 10:59 pm

Removed the thermstat. It ended up fluctuating tho it never seemed to go as low as before and doesnt seem to be as often. I didnt drive too far. Store, gas, etc. So do I assume stat is ok? What's next? I'm having what might be a fuel/fuel pump issue as well. hesitatiion when accelerating. Not sure if the 2 are related in any way? Oh and license plate light is on when hatch is open but goes out when hatch is closed halfway :? That one is annoying. I dont think I can deal with that. Dont even want to think about it. One day (problem) at a time.



Post Reply