thermostatic switch question
 

Dear Friends
I am still struggling to regulate my cooling/heating system after fitting a thermostat where there wasn't one before. Two thints strike me as odd.

1. The temperature of the water in the system has not risen at all and still sticks with the temp gauge needle just above the first, lower marking.

2. At this point, the fans come on, which strikes me as too early.


SO, here are my questions for those willing to reply.

- Where should the needle be for normal operating temp for the engine? Midway?

- WIth the needle just above the lower marking, could we assume this is only warm and not enough for hot air to blow through into the car?

- How common is it for thermostatic switches to come on too early?

- Can one be changed without removing the radiator?


thanks in advance to those good people who have the patience for all this and want to share their knowledge. it's greatly appreciated.


MJ in Beirut

The guage could be off or the sender bad. A couple of other things to check first. Do you have access to an infrared thermometer to check the temp on the upper hose? Is there heat in the car? Is the cooling system building pressure?

If the gauge is off it might be bad, the sender could be bad, or maybe the needle just needs a gentle little twist to recalibrate it. Watch how much it moves as it warms up. It should move about 1-1/2 to 2 marks as it warms up. Normal operating temp is 1/3 to 1/2.

don't trust the gauge. use a real thermometer to see if it is running right. it should run 100 degrees F over ambient temp, or 15 degrees above the thermostat point, whichever is higher. there should also be at least a 30 degree F difference between the inlet and outlet of the radiator, but not more than 70 degrees F after the thermostat has opened.

I dot have access to one of those, no, sadly. When you say 'sender' do you mean the temp sensor in the block?

The temp on the top hose is not as hot as it should be. Even i can feel that.

No heat in the car

It's not getting to the 1/3 mark.


MJ

Direct answers to your questions:

1. The temperature of the water in the system has not risen at all and still sticks with the temp gauge needle just above the first, lower marking.

Between first white mark and center mark

2. At this point, the fans come on, which strikes me as too early.

No, if fans are coming on and AC system is off, that's good.

SO, here are my questions for those willing to reply.

- Where should the needle be for normal operating temp for the engine? Midway?

- With the needle just above the lower marking, could we assume this is only warm and not enough for hot air to blow through into the car?

No, your heater valve may not be opening, or your heater system has some other problem.

- How common is it for thermostatic switches to come on too early?

Pretty rare.

- Can one be changed without removing the radiator?

Yes.

These are generalized instructions.

Since you don't have a thermometer to measure coolant temp, try this:

1. From cold engine start, put you hand on the hose that goes to the thermostat to feel the temperature. It should be as cold as the rest of the engine.

2. Remove your hand and then check the hose a minute or so later. It will feel cold/cool/warm.

3. Keep checking the hose going to the thermostat. At some point it should suddenly get hot.
This means that the thermostat has opened, and the water pump is circulating the coolant.
It will not have anything to do with when the fan(s) come on.

If you feel the thermostat open, and the gauge still reads low, you may need to replace the sender, or check the wiring going to it.

For assistance, go to Clark's Garage Home Page
Click on "Garage Shop Manual" on the left side, then under the red labeled "Engine" column, scroll down to "Cooling System." There you will find help.

I think you might be on the money as the levers for the heater don't feel as though they are connected. Is there an easy way of checking them without removing the whole dash?
Also, by your own post, my car is running a little cooler as it only gets to the first mark and not close to inbetween the 1/3 and half way mark.
Still don't think i have a wrong thermostatic switch?

thanks

MJ

the 944 gauge doesn't show "normal range" like newer cars...it shows actual temperature.
first line is ok if you are in cool weather, which you are right now in Beirut.

that is still warm enough to make the heater work.
the low-temp fan switch comes on at about that first mark, so i suspect that is what you have.

SO that would suggest the heater flap itself is possibly not switched on (the arms are not connected). Any idea if that is an easy job to do?

The heater valve is at the back of the engine behind the oil filler cap and under the intake manifold, you should be able to easily see if the cable from the cabin is connected or not.

thanks Vrocket2. That would normally have been enough detail but i still can't see it. Can you be even more specific. Is if immediately underneath the last tube of the manifold itself? Can it be seen from leaning onto the engine bay from the side and looking from above? What does it look like exactly?


thanks for your patience

MJ

85.5+ is vacuum-actuated and earlier cars and 924S's are cable actuated IIRC. There is a hose going into a valve almost shaped like a top or a cone, and then a hose coming out of it going into the heater core through the firewall. It's almost in your direct line of site when you are trying to observe the OT mark on the flywheel where the speed/ref sensors are on my car, which is a 924S and would be similar to a pre 1985.5

i have found such a hose with a tap, but that is on the other side next to the exhaust manifold. THe one you described is in the OTHER side right next to the oil filler. My 944 is 1986. Do you think there is another one down there?

That's the one! It will lead you to the heater valve if you follow it.

it jsust goes into the car firewall. The valve you are talking about must be inside the dashboard

From what I recall the temperature sensor activates a solenoid under the dash. This solenoid connects to the vacuum reservoir via a hose through the dash on one side. The other side also goes into the engine compartment and connects to the heater valve. These are small vacuum lines. You should hear the solenoid click if it is working. The click will be up and to the left of the glove box.

Beirut, I would go back to posts 2, 3, 4 and 6 above and focus on the gauge and the thermostat. I don't think the heater valve is significant right now.

If you determine your thermostat is working properly and you are not getting heat, then start worrying about the heater valve which incidently on some models could also be located under the distributor on the water pipe.

i think it must be the heater levers themselves on the dash. They are not connected so i have to assume tha they are in the off position and the tiny army which connect them have been disconnected.

It's a hot country and sometimes people do dumb things like this, especially mechanics.

If anyone has any advice how to peal off that panel and have a look, i would be v grateful


MJ

The sliders are electric switches so there is very little resistance to move them. Therre are two electric motor actuators under the dash that move the internal flaps for defrost and heat adjustments. Sometimes the motors go bad.

For the temperature of the air there is the rotary switch and the heater control valve which is in the 3/4" diameter heater core coolant line near the firewall or near the distributor. It is vacuum controlled. (google 944 heater control valve for a picture)

There is a very complicated electronic gizzmo (climate control module) that controls all of this that could also be bad.

Look in the drivers footwell and you cna watch to see if the blend door lever moves when the slider is moved.

look in the engine compartment to see if the heater control valve moves when the knob is turned.

Have you looked at Clarkes, there is a good write-up there about all of this.

From Clarks Garage --> Garage Shop Manual (top right) --> Temperature Control Removal and Replacement

Introduction
This is a procedure which I've had requests for many times in the past. I've simply put off writing this procedure for some time. If you need to replace your clock, cigarette lighter, temperature control unit, or light bulb for the clock or cigarette lighter, this is the procedure you need to use.

Tools

Stubby Phillips head screwdriver
Regular Phillips head screwdriver (optional - may use stubby Phillips for all)
Small flat tip screwdriver
Small set of needle-nose pliers
Temperature Controls Removal

1. Remove the control knobs (4) for the temperature control unit.
NOTE
Be extremely careful when removing the fan speed control knob. It has a light bulb behind it and it is very easy to break the bulb or the retaining tabs for the stem of the control knob. It may be necessary to slide a small flat tip screwdriver behind the control knob and apply pressure gently while pulling the control knob off the stem.

http://www.clarks-garage.com/graphics/trim-front3.jpg

2. Remove the temperature controls cover by carefully sliding a small flat tip screwdriver under each outside edge to loosen the trim piece.

http://www.clarks-garage.com/graphics/trim-front4.jpg

3. Behind the temperature control unit cover you will find four (4) Phillips head screws which hold the unit in place. Remove the screws to slide the control unit out.

http://www.clarks-garage.com/graphics/temp-control.jpg
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