850 non-turbo with temperature problem

[fk2001]

Hello everyone

My 850 non-turbo has developed a temperature problem. During the last few months the temperature gauge has stopped moving all the way up to the 3 o-clock position.

However at bumper to bumper traffic the gauge does go the normal position but drops again when driving on highways. That sounds just like a stuck-open thermostat, so I replaced that, but the problem persists.

I thought the temperature sensor may give a false reading, so I wanted to verify this. I measured the temperature on the thermostat housing right after I came to a stop. Temp. gauge was at 4 o’clock position and the temperature was 82 degrees.

I let the car idle, watching the gauge and the thermometer. At the guage´s 3 o-clock position the temperature reached 104 degrees. A little later at 107 degrees, the fan came on. It ran until the temperature dropped to 104 degrees.

In the Haynes repair book it says that a 90-degrees thermostat starts to open at 90 and is fully open at 105 degrees. It doesn’t say anything about when the fan comes on, but it seems logically that the fan starts after the thermostat has opened max.

Can anyone confirm what the normal running temperature is for the engine when the gauge stays at the 3 o-clock position?

And at what temperature is the fan supposed to come on?

Thanks for any help.

[capt jack]

I doubt that measuring the temperature of the outside of your thermostat housing will actually tell you very much - it's the temperature of the coolant inside that's important - which is what the temp sensor should be measuring.

When you changed the thermostat did you get the orientation right, and did you replace the rubber sealing ring? If the sealing ring doesn't seal, it's like driving with the thermostat half open all the time - and you'll get over-cooling.

It's also possible that you've got an air-lock in the cooling system. When you changed the thermostat did you lose any coolant? If so did you replace it, make sure you ran the engine up to temp with the heater controls set to the hottest setting? Then did you get any air out by gently squeezing the radiator top hose, and carefully releasing the pressure by slightly undoing the water tank cap?

It's not impossible that your new thermostat is faulty too!

If the ECT - engine coolant temperature signal - is wrong then the ECU should store a fault code, which it will also do if the engine cooling fan is faulty. Has any warning light shown up? Can you check for any stored fault codes?

But I think that the place to start is to re-check the installation of the new thermostat, and make sure that the rubber seal is in place OK.

The other thing to check is that you don't have any coolant leaks of course.

Cheers

Jack

[960kg]

Originally Posted by fk2001

Hello everyone

My 850 non-turbo has developed a temperature problem. During the last few months the temperature gauge has stopped moving all the way up to the 3 o-clock position.

However at bumper to bumper traffic the gauge does go the normal position but drops again when driving on highways. That sounds just like a stuck-open thermostat, so I replaced that, but the problem persists.

I thought the temperature sensor may give a false reading, so I wanted to verify this. I measured the temperature on the thermostat housing right after I came to a stop. Temp. gauge was at 4 o’clock position and the temperature was 82 degrees.

I let the car idle, watching the gauge and the thermometer. At the guage´s 3 o-clock position the temperature reached 104 degrees. A little later at 107 degrees, the fan came on. It ran until the temperature dropped to 104 degrees.

In the Haynes repair book it says that a 90-degrees thermostat starts to open at 90 and is fully open at 105 degrees. It doesn’t say anything about when the fan comes on, but it seems logically that the fan starts after the thermostat has opened max.

Can anyone confirm what the normal running temperature is for the engine when the gauge stays at the 3 o-clock position?

And at what temperature is the fan supposed to come on?

Thanks for any help.

The engine will run at about 91 or 92 centigrade in normal weather and use.
The fan comes on at 107 C

The running temp will drop according to what the temp of the airflow is going through the radiator, that is why the thermostat has room for automatic adjustment, fully open at 107 C

Did you fit a new Volvo thermostat, or are you going to?

[fk2001]

Jack,
I used a thermocouple wire to measure the temperature which should be pretty accurate for measuring on metal surfaces. I use this setup in my daily work. I also believe the thermostat housing’s temperature represents the coolant waters temperature as the thermal resistance for water and metal is much lower than the air around the housing.

About the orientation, the Haynes didn’t mention anything about this. But I’m certain that it’s not upside down if that’s what you mean.

I didn’t lose any coolant, I drained 2 litres before replacing the thermostat. But I did have a little bit of a challenge getting it back in, but by squeezing the top hose as you mentioned, the coolant eventually sank down. I reused the coolant and I believe it sits at the same level in the reservoir as before.

There are no warning lights, but I don’t have a code reader. How is the ECU supposed to know if the ECT is off? Does it have another reference?

As you suggest, I will check the thermostat installation. I did use a new rubber seal, and I felt a bit of compression when I tightened the screws, so I assume its sealing properly.

What about checking the thermostat in hot water to see if it’s opening too soon? Shouldn’t I be able to see when it starts to open? I just inspected the one I took out. This one is not completely closed. When I shine on it with a torch, light comes through. There is probably a 0.5mm opening half way around. I don’t know if this is to be expected. By the construction, I doubt it can seal completely.


960kg,
If you are sure that the fan comes on at 107, and my measurements are correct, my ECT should be ok, I guess.

I fitted a Whaler thermostat as recommended. This is actually my fourth thermostat in four years (but my first one from Whaler). Every time the problem is the same, the gauge sits lower and lower, and after I fit a new thermostat, the gauge is back to 3 o-clock position – just not this time.

Thanks to both of you for your comments.

Frank

[capt jack]

Hi Frank

Interesting questions. Sounds as though things are working almost OK but not quite.

One thing does surprise me and that is that you 'felt the compression' as you tightened up the housing bolts. When I've done this job I don't remember that sensation particularly. As for orientation, sorry, yes I did mean is it in the right way around? I don't mean to question you at all, but we've all done strange things without meaning too!

The rubber gasket is grooved, and is fitted around the outer rim of the thermostat body before the complete assembly is dropped into the lower half of the thermostat housing.

Is there any chance that the rubber ring is not seating properly around the thermostat?

And yes, it will be possible to see the thermostat working by dropping it cold into a pan of boiling water on the stove in the kitchen. Just make sure that Mrs Frank is OK with this idea first!

I think it's right to say that if the ECU doesn't get a valid reading of coolant temperature it will record a fault code.

Otherwise, have you checked the temperature of the top and bottom hoses off the radiator, and where the heater hoses go through the engine bulkhead?

If all is well then with the car's heater fully ON, the temperature of all the hoses should feel pretty much the same. If one of these hoses is much cooler than the others you may have a partial blockage in radiator or the heater matrix.

Cheers

Jack