There are several thermostats for the 240's - 91, 88, 81 Degree C. I understand that thats when they begin to open. But, do they control the final stabilized operating temperature after car is completely warmed up?

In theory, once they are full open they should all allow the same flow - but I may be wrong. The various ones just control how fast it stabilizes?

During warm up my gauge climbs to about 10 o'clock then slowly settles to 9:30 position. Would a lower temp thermostat get it to 9 o'clock?

Thanks

As long as it is not extremely high on the gauge and it rides about the same place after warm up I think it is fine. I run an 87 degree one in all my Volvos.

Removing the compensation board removes a trouble maker from the system:
http://cleanflametrap.com/tempFaker.html
--
Any twenty minute job is just a broken bolt away from a three day ordeal

In case it helps, here are some notes on thermostats from my collection:

Thanks all. I am using a CALOROSTAT - 87 degree - once stabilized needle about 9:30 - so will keep an eye on things. May replace the fan clutch since its cheap and easy as well.

Hey Mike have you dealt with the Temp compensation board in the cluster yet?

No, the needle is quite stable just a little high - 9:30 and the rad is several years old and clean - but I am changing the fan clutch - its very old and corroded

Removing the temp comp board will give you an actual temp read all the time.

Not just removing but bypassing.

Some feeble minded person like myself might not understand why their gauge suddenly doesn't work.


--
'79 242, '84 DL 2 door, '80 DL 2 door, '89 DL Wagon, '15 XC70 T6 AWD

By jumpering pins 1 an 3 with a piece household wire

There is a way to do this bypass without disassembling the cluster.

Scroll to External Wiring Method:

Notes on the Temp Faker - Or That Temp Comp Board

--
Art Benstein near Baltimore

Did you know actor Raymond Burr had a brother who was a lumberjack? His name was Tim.

I do not know about the 2 series, but in the 700 series they offer two thermostats.

The one with the lower temperature rating is use for turbo engines as there is more equipment in the engine compartment, including a heat producing turbo.

Interestingly, in one of our 850s a thermostat failed in the open position (it was designed to fail open ) on the highway, the temperature actually went down at speed. In that case the thermostat would close some or all the way.

BTW - I read about a high performance BMW that had two thermostats and a hose to bypass the radiator when flying along an autobahn in the mountains of Germany to keep the engine hot.

If your temperature gauge has a circuit to stabilize its reading, the reading that you see if it is not normal, is probably worse than you think.

When I got my 544 I was surprised to see how much the temperature gauge changed under conditions such as climbing a hill, or coasting.

Hi, Mike

I agree with AmazonPhil that you are possibly running to warm due to a dirty radiator. It’s either the outside fins or the core tubes inside that are clogged.
If it’s an older radiator or tap water use and with hopefully antifreeze but it’s clogged
.
With a 92 C thermostat that working properly the needle should be horizontal or slightly less.
What you describe is overshoot of which is common with some less expensive thermostats or an aged one, especially, if it’s slow to rise up and stays lower.
By it staying up and not overheating the radiator comes into question quite easily.

If you want to define the actual opening of a thermostat “the degree stated” is when the thermostat first open or cracks loose from the seat circle.

When testing mine in vegetable oil the observation is more accurately done as oil is more stable than an open pot of boiling water. Radiator water is under pressure so thereby no bubbles.
So, What water is up against the wax pellet is a solid transfer of heat.

The mass of wax continues to expand in its chamber and that precise volume moves the diaphragm against a calibrated spring.
A degree or so will expand the mass more but it’s still a small amount of mass.
The coefficient of expansion and precision dimensions of its vessel its in are crucial IMO.
All springs have a tolerance range within a specification curve.
The curve must be similar to a wax consistency, of all things.

Same principles are still reliable. Imagine that.
The type of materials are used in combination and unit is, like tuned, for repetitive performance.
How long is that, is the bigger question, that I see as most important.

I have a preference to what Volvo used from the factory and back in production they used WAHLER that is now owned by Borg Warner.
Despite the change of hands, they have kept using brass and copper components and still put a date of manufacture stamped in each thermostat.
There must be a reason and I have noted no other manufacturers doing it. Why?
I have left mine in so long, that I’m amazed that one was 17 years old from 1978. I still have it but I changed it out to a new one years ago just from fear that I knew it had to be old. I’m the original owner but I have many more 240s that I have bought used.
Those developed issues and they had other brand thermostats every time.
Since no date and a failure of repetitive needle movements of my gauge I give respect to Wahler products.

I’m really glade that you are that aware also!
Between the coolant gauge and a voltmeter gauge they are a “navigator of highways” best information to keep an eye on!

On an airplane the temperature and voltage gauges are even more important.
Using the BRICKBOARD forum is like having a good radio to get requests answered.

Phil

the thermostat will open sooner and allow more flow sooner if it is a lower temp one. i think it should also affect the operating temp of the engine. keep in mind your issue could be a plugged up radiator, or a head gasket issue,and the temperature sender could be off. some may choose to change it seasonally but I always found that to be a hassle.. maybe you want different ones to match your climate. a warmer one might make the heater work better or a cooler one might make some difference in keeping things cooler.

watch for any mysterious emptying of the water bottle or if you see water dripping from the exhaust or the sweet smell of antifreeze in the exhaust, if you see that suspect head gasket issues, often the first sign is that the temp will fluctuate in an odd manor or overheat. another sign is the need to add water and that can be blowing through the head gasket into the combustion chamber and out the exhaust. you may also see the level in the bottle going whacky , overflowing or emptying as the air gets in the water system which is normally a closed loop.

my 240 blew a head gasket a short while ago. second time. the first time I rebuilt the whole engine and that was ok for a decade or two but it happened again. I tried one of those head gasket repairs where you empty the rad add the stuff run the engine and it's supposed to plug the leak.. It turned out to be a waste of time and so I'll plan to pull the head off, maybe have the head surfaced if needed. waiting for nicer weather now..