collant gauge drops off, any ideas?

[rahul]

Hi guys

I Noticed this yesterday on the coolant temperature gauge...whenever i turn the car off and back on...the gauge goes to the middle (if the cars warm) then after about 5-6 seconds the gauge drops off to 0 but no noticeable changes with the car itself...any ideas? I posted on Facebook as well, and suggestions have been a faulty coolant sensor or the cluster itself.




thanks

[JamesT5]

If your car is OBD2 then get a Vida read on the ECU, it will tell you if you have a fault relating to the sensor. See my thread as I've just changed mine along with the Thermostat.

[rahul]

Thanks alot, another thing i noticed was the internal fan and heating have stopped working...any clues?

[JamesT5]

Thanks alot, another thing i noticed was the internal fan and heating have stopped working...any clues?

Internal fan? Check the fuse for the fan blower unit (it will tell you in the handbook), if that's in tact then it could be fault with the motor for the fan, a resistor or something.

As for the 'heating', are your front carpets wet? Have you checked your coolant level? If there is no coolant or very little and just 'air locks' then your engine would actually overheat but you'd get little or no heat out of your air vents. You'd also crack the engine block.

There could also be an issue with the water pump not pumping the coolant around, again, it's likely your engine would overheat.

Start with the basic checks and go from there, so coolant levels, fuses, any obvious leaks etc.

[MoleT-5R]

Internal fan? Check the fuse for the fan blower unit (it will tell you in the handbook), if that's in tact then it could be fault with the motor for the fan, a resistor or something.

As for the 'heating', are your front carpets wet? Have you checked your coolant level? If there is no coolant or very little and just 'air locks' then your engine would actually overheat but you'd get little or no heat out of your air vents. You'd also crack the engine block.

There could also be an issue with the water pump not pumping the coolant around, again, it's likely your engine would overheat.

Start with the basic checks and go from there, so coolant levels, fuses, any obvious leaks etc.

ok to start with the obvious, what model volvo are we talking about, as this is looking electrical as far as I see

[rahul]

Haha so sorry. Its a 98 s70 2.5t manual

[LeeT5]

Well? Did you sort it? What was it?

I bet it wasn't a cracked head, water pump, fuse for the fan blower unit, resistor, wet carpets or coolant level.

I do know it was an electrical fault - because a mechanical fault would not cause the gauge to drop like a stone, as per your video.

[claymore]

Well? Did you sort it? What was it?

I bet it wasn't a cracked head, water pump, fuse for the fan blower unit, resistor, wet carpets or coolant level.

I do know it was an electrical fault - because a mechanical fault would not cause the gauge to drop like a stone, as per your video.

How can you say that, our resident 'expert' has said it's probably a cracked block, or possibly the brakes need bleeding. (there should be a disclaimer on the forum to warn new users to ignore advice from JamesT5,) unless it is backed up by at least two other respected forum members.

[Ettienne]

It's funny how he offers advise to newbies that may just follow blindly his words of wisdom.

[LeeT5]

It's funny how he offers advise to newbies that may just follow blindly his words of wisdom.

[Wobbly Dave]

I would suspect a faulty water temp sender as the gauge clearly works (at least initially) - especially if this is repeatable. Can't be a leak because if the car was leaking & the sender and gauge were working - then the temp would go up.
I would also be temped to change out the binnacle to rule out any fault within the dash itself.

ps I have a spare binnacle from a 99 C70 - but I suspect there maybe small differences.

[LeeT5]

Can you correct the thread title spelling mistake please Dave. It's bugging me!

[Wobbly Dave]

I only wish I could but sadly I have no powers

[LeeT5]

Can you correct the thread title spelling mistake please Dave. It's bugging me!

I only wish I could but sadly I have no powers

Admin!!!

[stribo]

Clutching at straws comes to mind. If the heater's not working, why would the carpets be wet?

[RollingThunder]

A more logical test comes to mind if someone can confirm how the coolant sensor works on these...

Assuming its a (temperature triggered) variable resistor, then earthing out the wire to the coolant sensor should return the gauge to zero? Conversely, if you apply a voltage to that wire the gauge should rise? If we could get the correct test figures for full deflection, half deflection and zero deflection, then that should indicate whether the coolant sensor is faulty, or whether the fault lies elsewhere?

Thats where I'd be looking anyway, checking the integrity of the connection and doing this test - but only after finding out if the presumption is correct. If the sensor is current based, then of course this is all bull££££

[Harvey]

A more logical test comes to mind if someone can confirm how the coolant sensor works on these...

Assuming its a (temperature triggered) variable resistor, then earthing out the wire to the coolant sensor should return the gauge to zero? Conversely, if you apply a voltage to that wire the gauge should rise? If we could get the correct test figures for full deflection, half deflection and zero deflection, then that should indicate whether the coolant sensor is faulty, or whether the fault lies elsewhere?

Thats where I'd be looking anyway, checking the integrity of the connection and doing this test - but only after finding out if the presumption is correct. If the sensor is current based, then of course this is all bull££££

As above & engine earth strap, that's my guess.

[LeeT5]

As above & engine earth strap, that's my guess.

No, no, its definitely a cracked cylinder head.