Engine: 70 T5: New thermostat, engine temp still dropping when coasting

[MikeS100]

So I got my new thermostat fitted this evening, it seems to be working ok as the top hose stayed cool until the engine temp was up to normal and then got hot suddenly which you would expect. But, when I went out for a test drive the temperature needle stayed dead centre for most of the time but dropped to cool on a long downhill stretch. So, if the thermostat is working properly what else could cause this? I don't think there is any air in the system as I followed all the proper procedures for refilling the coolant and got plenty of air out.

Any suggestions as to what else I could look for?

[Jas16]

The needle dropping is not a big problem. my s70 does the same thing and the 850 I had before that did the same too. Ford escort as well. Personally nothing to worry about unless the needle goes above the perpendicular to the red and if the needle takes ages to lift from the bottom. Over winter, going at 70 on the mway the needle was barely a few marks off the bottom, mainly down to cool air cooling the engine and I guess the thermostat not needing to open. Thats my point of view though

[blackrevolver]

Originally Posted by Jas16

The needle dropping is not a big problem. my s70 does the same thing and the 850 I had before that did the same too. Ford escort as well. Personally nothing to worry about unless the needle goes above the perpendicular to the red and if the needle takes ages to lift from the bottom. Over winter, going at 70 on the mway the needle was barely a few marks off the bottom, mainly down to cool air cooling the engine and I guess the thermostat not needing to open. Thats my point of view though

Jas am surprised you say that (although you may be right) but from what i read it should always stay at the middle mark once warmed up..

When i was having issues with mine, it would act in the same manner as yours on the highway, if i drove at high speeds, it stuck open, if i drove around town it would be fine.

Since i had my thermostat changed, it has never dropped below the middle mark once the engine has warmed up.

[MikeS100]

I've been thinking about it tonight and I've got a feeling the thermostat has dislodged and is now not sitting correctly in the housing It was quite awkward getting it lined up because of the design, it's not like a normal thermostat that just sits in the housing, if it's out a bit it won't seal properly so I may be taking it off again at the weekend to have another look

[blackrevolver]

Mike, did you use a genuine part? reason i ask,is that when i had mine changed and asked on here about what the problem was, everyone said to use a genuine part, as the aftermarket ones tend to fail quite quickly.

[deathrider311271]

if you bought a gen volvo one there are 2 types, for the turbo model there is anyway, one rared at 92 degrees and one rated at 87/88 degrees. The later one being for extremely hot climates and towing caravans.

When i replaced mine 2 years ago Volvo gave me the wrong one they gave me the 87/88 degree one, i didnt have this info at the time so just left it, anyway i have just fitted the correct 92 degree thermostat and the car runs better, better mpg opens and shuts as it should.

If on the other hand you have bought an aftermarket one, good luck, my original after market one lasted 3 days before doing exactly what yours does, where as both volvo ones stay bang on 3 o clock no matter what the outside temp is.

There should also be a bypass ball bearing, this needs to sit facing the front of the bonnett if i remember correctly

[OvlovS70]

Must concur, mine is rock solid with the gauge at three o'clock, well a smidgeon above since I replaced my original which had lasted 15 years.
I have been following your thread on this and see you have had to do the whole housing, great deal on the parts by the way.
You may well be correct in your thinking about it being dislodged.
Could your temperature sensor be at fault? Not sure at all about the set up of your model but maybe someone else can elucidate on this?
Cheers

[MikeS100]

It's genuine Volvo from my local main dealer, you can't get an aftermarket one for mine as it's the one where you have to buy the complete housing. I left the original housing in place as it is very awkward to remove and I think it means removing part of the power steering, but looking at the new one it has extra raised up bits moulded into it which would probably stop it from becoming dislodged so they are obviously aware that can happen and have changed the design slightly

[MikeS100]

Originally Posted by OvlovS70

Must concur, mine is rock solid with the gauge at three o'clock, well a smidgeon above since I replaced my original which had lasted 15 years.
I have been following your thread on this and see you have had to do the whole housing, great deal on the parts by the way.
You may well be correct in your thinking about it being dislodged.
Could your temperature sensor be at fault? Not sure at all about the set up of your model but maybe someone else can elucidate on this?
Cheers

I guess it could be a faulty sensor, but now I have looked more closely at the new housing I am thinking I will need to fit this as well and in trying to save myself some work I have actually ended up with more to do

I'm going to start another thread about removing the power steering pump as I think I will have to tackle this at the weekend. Once that is out of the way changing the thermostat housing should be relatively easy.

[960kg]

Originally Posted by MikeS100

So I got my new thermostat fitted this evening, it seems to be working ok as the top hose stayed cool until the engine temp was up to normal and then got hot suddenly which you would expect. But, when I went out for a test drive the temperature needle stayed dead centre for most of the time but dropped to cool on a long downhill stretch. So, if the thermostat is working properly what else could cause this? I don't think there is any air in the system as I followed all the proper procedures for refilling the coolant and got plenty of air out.

Any suggestions as to what else I could look for?

That is normal!!

If it was a very long stretch like down the M20 hill at Wrotham Hill, Kent it will drop as mine does.

When you have no throttle the ECU cuts off the fuel so therefore you have NO combustion happening to heat up the coolant and so it gets colder and the needle will drop.......Simples.

The same thing happens in Winter with a cold headwind into the radiator the engine coolant system cannot overcome the extreme cold air so it runs cooler and the needle will be lower. If you then turn around and have a cold tail wind the needle will read normal in the middle as the cold wind is now behind you.

Remember old school motors with radiator blinds?