Temperature gauge reading low whilst at speed...

[Turbodave]

Car is a 1996 850R, standard.

On the motorway, the temperature gauge will sit roughly at 4pm (if that makes sense) however once in town/stationary it'll rise to nearer 2pm. I'm assuming the needle should sit around the 3pm mark, ie halfway on the gauge even on the motorway.

My first thought was the thermostat, either sticking open or some chomper has fitted a cool running thermostat which in Scotland, is as much use as an inflatable dartboard. So, going to grab a thermostat and pop it in over the weekend but anything else that it could be or I should be doing?

Fuel economy seems ok, well... it's brutal but also normal for a T5. Averaging around 32mpg on a run so assume the coolant temp sensor is fine, though again the engine running slightly cold won't be helping in the MPG stakes. Or, perhaps the sensor is dicky and is giving erratic readings?

Any thoughts?

[t5_monkey]

sounds like a ropey sensor they are always the first thing to go.

[Turbodave]

No problem chap, I'll perhaps just do it and the thermostat as a matter of course.

Similar topic but new questions, do these car have a live date function? Ie, with an OBDII reader can I access various data lists... ie, could I connect to the car and view what the ECU is seeing from said sensor? Eg, if the gauge says 70deg, the ECU is seeing 70deg and a laser thermometer on the housing says 95deg then we know there's an issue. Similarly, if the ECU sees the coolant temp rising from cold but starts spiking positively or negatively?

Or are the 850's not that advanced?

[Dan850r]

I can read live date with a delphi diagnostic machine i have, i can have a look if it reads coolant temp

[Dan850r]

Mines an obd2 850

[Turbodave]

Same as mine chap, definately OBD2 as I have an OBD2 adaptor lead for my laptop for use in modern Vauxhalls. I've popped a thread up in 'car chat' as I'm after the Volvo software, or looking for any recommendations though I do also have a hand held scanner so I'll give that a shot and see if it works too.

[glock19]

For low temp, it could be the thermostat.
For high temp, it could be thermostat and faulty radiator fan, not spinning as fast as required.

[wegal]

Stuck stat would cause both problems, especially if it isnt stuck fully open or fully closed.

[Dangerous Dave]

I would do the thermostat first and see how it gets on, mine was doing the same and it was the thermostat.

[Turbodave]

Drove the car again today. It takes a fair time for the gauge to react and start climbing and on the motorway it does sit low but as soon as the speeds drop, the gauge climbs up towards 90deg. Soon as the speed increases it drops right down. It's consistant with the speed so I'm also leaning towards the thermostat as I think a fault sensor would give merractic readings. I'm on the case.

Cheers

[Dangerous Dave]

Thermostat is cheap enough to change first, does sound like its stuck open if it takes ages to warm up and gets warm when in traffic.

If the sensor was playing up you would also experience poor mpg and other performance problems.

[Turbodave]

Thermostat is cheap enough to change first, does sound like its stuck open if it takes ages to warm up and gets warm when in traffic.

If the sensor was playing up you would also experience poor mpg and other performance problems.

Fuel economy isn't great but I think it's normal for the car. It runs fine, doesn't reek of fuel when it starts etc but again, if it's running cold due to the thermostat being stuck then that will also creating a slight overfuelling issue regardless if the coolant temp sensor is working or not.

[Dangerous Dave]

Yeah, didn't think that one through fully did I lol.

[960kg]

Fuel economy isn't great but I think it's normal for the car. It runs fine, doesn't reek of fuel when it starts etc but again, if it's running cold due to the thermostat being stuck then that will also creating a slight overfuelling issue regardless if the coolant temp sensor is working or not.

Everything seems if that and if this......the parts involved are so reasonably priced from Volvo that you will recover any money spent with better performance including economy. But only buy Volvo.

You must have doubts as you would not of posted!!

Bomb is correct do your thermostat first £18`ish then if no change do the Engine Temp. Sensor £36 `ish. and then your ok for thousands of miles.

[Turbodave]

Woah! £18... sheesh, is it gold plated? Picked one up earlier for under a fiver so off to fit it shortly. Also got a shot of a mate's OBD2 scanner but it's not communicating with the 850. It'll talk to the V70 (1999) but only ABS and SRS.

I shall report back...

[960kg]

Woah! £18... sheesh, is it gold plated? Picked one up earlier for under a fiver so off to fit it shortly. Also got a shot of a mate's OBD2 scanner but it's not communicating with the 850. It'll talk to the V70 (1999) but only ABS and SRS.

I shall report back...

Of course everyone to there own but the Volvo one is reliable and will last you out!

The cheap one could let your engine overheat eventually if you don`t notice it and then more expense! Some people you just can`t help.

[Turbodave]

Of course everyone to there own but the Volvo one is reliable and will last you out!

The cheap one could let your engine overheat eventually if you don`t notice it and then more expense! Some people you just can`t help.

Who makes the 'Volvo' thermostat? Serious question... is it made in a Volvo manufacturing plant using different meterials and techniques, or like the vast majority of car components, is it made by a third party who also make parts for various other manufacturers and also the after-market parts industry such as Whaler or Vernet

For example, many cars share common parts... a Saab heater motor is the same as the one found in some Vauxhalls. Most air flow meters are made by Bosch and the vast majority of bearings are made by SKF and similary, Sachs, Bilstein, Boge, Nippon Denso, Hella and so on all manufacture components for new cars and also the aftermarket supply.

Does the fact X part comes in Y box make it any better than another part? Yes, I accept some parts are much cheaper quality and should be avoided however a vast majority of parts are made to the exact same standards as the OEM component, possibly even by the same manufacturer. For instance, an 850 front indicator is made by Hella. The fact it comes in a nice blue box with Volvo on it doesn't make it any better than a Hella unit from say, Unipart or GSF.

As for an aftermarket component, in this case a thermostat, letting my engine overheat... I suspect the gauge heading north would be the first clue and secondly, what's to say a Volvo 'genuine' part wouldn't suddenly stick shut and create a similar situation? Parts can and will fail, the colour of the box and the price on the invoice won't change anything. I've used QH stats for many years, never had an issue with them.

But, I respect your opinion.

Cheers

[Turbodave]

New thermostat is it, old one is out and was a Whaler stamped one.

The temperature gauge came up much faster and hovered around the midway point and stayed there at speed to, whereas before it'd drop right down.

Came back, let the car run for a couple of minutes and waited for the fan to kick in. No fan kicking in and the gauge remained resolute just over the midway point. Disconnected the ECT plug, temperature gauge dropped out and the fan fired up. Reconnected it, gauge to just beyond halfway, fan went back off.

Just checked the resistance over the coolant temp sensor and currently it's around 220 Ohms which according to this...



...would suggest the coolant temp sensor was seeing around 90 to 92deg and again, according to the above the fan shouldn't be kicking in at low speed until 106deg and then high speed at 114deg. Both of which seem a bit hot but hey ho.

I'll take it a run again tomorrow and check the resistance over the sensor when it's properly hot (and first check it stone cold) but I was expecting the gauge to keep climbing when idling, past 3pm and then peak as the fan kicks in then drop back down...

Soem interweb searching and a call to an old colleague would suggest that's nott he case and the gauge will rarely climb beyond 3pm, even if the temperature has reached and indeed exceeded 90deg (thermostat opens at 91deg) and even with stage one fan kicking in a 106deg and stage two at 114deg, the gauge will remain at 3pm.

I stood and let it idle for a good few minutes after a good blast whilst watching the temperature gauge. It refused to go beyond 3pm and the fan still didn't kick in. I bottled out and decided the fan was dead - by which stage the top hose was too hot to hold, so started driving to get some air through in however based on the above... perhaps that was perfectly normal?

Any thoughts on that one?

Cheers

[Turbodave]

Now on 600 Ohms... so just under 60deg at the sensor according to that graph. Unfortunately I can't confirm that as a) I don't have a laser thermometer and b) it's outwith the range of the thermometer she uses to check the wee mans temperature. I'll need to wait till it hit 30ish degrees and try it again.

If I don't reply, I've been rumbled by an irrate other half... so ring the police please.

[Jimmie]

Glad your happy with your purchase and getting it into shape.
Just as well it was an 850 that needed a stat and not a phase 2.
You would not have had much change out of three figures for one.
A snip at the price would you say?