Overcooling? Where does your temp gauge sit?

[Laird Scooby]

Originally Posted by martin calva

To my amazement, the car had no thermostat. And, in view of the difficulty of undoing the bolts on the thermostat, housing it had been like that for a long time.

Surprised it didn't warp the head and blow the head gasket - lack of a 'stat causes uneven cooling (and therefore heating) of the cylinder head which creates hot spots which lead to warpage.

Even a weal 'stat will protect the head as it restricts flow to hole in the middle of the 'stat which helps to even the temperature out.

Originally Posted by AllHailKingVolvo

My current 940 sits at just a hair past the midway point...maybe 53%. Never moves once warmed up, though. It could be that it has the 92deg stat in for NA cars and should have the 87. I'm not in a huge rush to check and change it as five degrees won't cause any loss of sleep, but will sort it soon enough.

If it ain't broke Phil, don't fix it! If you do have to change the 'stat, stick with the 92C version.

[Rversteeg]

I remember once having a sudden drop of the temp gauge when driving on the motorway. When leaving the motorway the dial went back to normal. When I took the thermostat out I found that the little aeration plug had become wegded between the valve and housing. Appearently its hole had worn out over the years allowing the pin to move too much. All solved with a new thermostat.
In the attached picture you can just see the little pin stuck between valve and housing.
Changing the thermostat is quite easy if you first drain the expansion tank with eg a syringe. No need to fully drain the system as the thermostat is quite high up and you will hardly loose any coolant.

[lnparry]

Originally Posted by Rversteeg

I remember once having a sudden drop of the temp gauge when driving on the motorway. When leaving the motorway the dial went back to normal. When I took the thermostat out I found that the little aeration plug had become wegded between the valve and housing. Appearently its hole had worn out over the years allowing the pin to move too much. All solved with a new thermostat.
In the attached picture you can just see the little pin stuck between valve and housing.
Changing the thermostat is quite easy if you first drain the expansion tank with eg a syringe. No need to fully drain the system as the thermostat is quite high up and you will hardly loose any coolant.

Hi Rversteeg, I'll look out for that. Does the thermostat housing have a paper gasket or just the rubber sealing ring around the thermostat?
Thanks,
LeeP

[Laird Scooby]

Originally Posted by lnparry

Hi Rversteeg, I'll look out for that. Does the thermostat housing have a paper gasket or just the rubber sealing ring around the thermostat?
Thanks,
LeeP

The thermostat has a proper sealing ring Lee, it has an internal groove that fits round the edge of the 'stat - advisable to use a smear of silicone grease on the edge of the 'stat and on the outside of the seal to help it find its water-tight position and to enable future remoal without need for slide hammers!

[Rversteeg]

It is not so much something you should look out for, but a possible explanation for the indicator to suddenly give a lower reading. A thermostat is more or less a wear part anyway, costing less than 20 GBP and quite easy to replace, so just go for a new one.

[bob12]

Thirty years on and still the original thermostat and water temp sensor on the 745 are working well with the temp gauge sitting nicely near the centre mark.

Only once was it really tested to the red when the back heater hose blew and, I didn't spot it until the car started to 'stutter' and steam also started to emit from the bonnet n/s edges!! Then I looked down at the gauges.

That's Volvo motoring.

Bob

[kelvinp]

Originally Posted by Rversteeg

I remember once having a sudden drop of the temp gauge when driving on the motorway. When leaving the motorway the dial went back to normal. When I took the thermostat out I found that the little aeration plug had become wegded between the valve and housing. Appearently its hole had worn out over the years allowing the pin to move too much. All solved with a new thermostat.
In the attached picture you can just see the little pin stuck between valve and housing.
Changing the thermostat is quite easy if you first drain the expansion tank with eg a syringe. No need to fully drain the system as the thermostat is quite high up and you will hardly loose any coolant.

Have to say, never seen a jiggle pin jam a thermostat before, but then I've only ever had to change one other dud thermostat before and that was a bellows type.

[lnparry]

Originally Posted by capt jack

For what it'll cost definitely change the thermostat. And from recent experience with our S70 if you can get a genuine Volvo one you'll be surprised at how little it'll cost - and it will of course fit and work perfectly.

But do go carefully if the stat housing is the same soft alloy as on the x70 five pot engines. It's easy to crack them with over-enthusiastic loosening of the Torx bolts - which themselves are made of soft chocolate.

As well as the thermostat I'd suggest getting a couple of spare bolts too, and then soaking the old in WD40 before attempting removal.

Jack

Hi Jack (and everyone else),

Soaked the studs and 10mm nuts with WD40 for the last few weeks. Top one came off a treat but the bottom one rounded off despite a quality socket. Looking at it I think it was damaged when last fitted (not me).

Any tips for getting the rounded nut off? Mole grips? Drill? Hacksaw? Access is not brilliant.

Cheers,
LeeP

[Ian21401]

Is it possible to cut one side of the nut off with a hacksaw or mini Dremel type saw or grinder. Without damaging the thread on the stud of course. I’ve done it once a long time ago on some other ruined nut somewhere but cannot remember where or when. Once there is only a thin piece of the nut against the stud I was able to turn the nut with whatever would fit over it, spanner or mole grip. The heat generated in the process may also assist. Just a thought.
I am planning to renew my thermostat ASAP as the temp gauge is reading about 30% when it used to read 50%. Although I haven’t noticed any reduction in the heater temperature.

[lnparry]

Originally Posted by Ian21401

Is it possible to cut one side of the nut off with a hacksaw or mini Dremel type saw or grinder. Without damaging the thread on the stud of course. I’ve done it once a long time ago on some other ruined nut somewhere but cannot remember where or when. Once there is only a thin piece of the nut against the stud I was able to turn the nut with whatever would fit over it, spanner or mole grip. The heat generated in the process may also assist. Just a thought.
I am planning to renew my thermostat ASAP as the temp gauge is reading about 30% when it used to read 50%. Although I haven’t noticed any reduction in the heater temperature.

Thanks Ian,

Yes, I have had a similar thought but I've seen some special "rounded nut removal"sockets on the interweb that I might have a go with first. They seem to have some sort of thread inside that bites into the nut.

When you do yours I would certainly endorse soaking with WD40 for a week or two beforehand as someone on here mentioned. The uppermost nut cracked off a treat. Cheers, Leep