After many summer months of using my TD4 with the heater control set to minimum, a few days ago I needed a boost of cabin heat and was most disappointed the result. With the Water temp gauge just below half way, I assumed correct running temperature but after connecting OBD, the water temp was reading between 65 and 70 degrees, much too low. I assumed a sticking thermostat (partially open)
Reading around the subject on the forums, the following points were noted.
1. Access to thermostat is a long job which requires removal of water pump (although there are reports to the contrary).
2. Don't be fooled by the electric radiator fans running whilst undertemperature. The engine fans come on whenever the A/C comes on and the A/C comes on whenever the heater control knob is in the demist (windscreen) or windscreen/footwell position and the cabin booster fan knob is on (1,2,3,or 4) - This fact is irrespective of the main A/C button - The A/C is comes on to aid demisting and cannot be overidden.
So after altering the heater to prevent A/C & fans coming on, I tried again, this time reaching only about 72 degrees, it was still running cool.
I really did not want the hassle of changing the thermostat but also wanted a toasty cabin for the cold months ahead.
Then I had an idea, what if I could force the water temperature above the opening temperature of the thermostat (about 85 degrees), maybe there was a piece of crud stuck in the thermostat when it last closed (or perhaps it closed incorrectly mechanically) therby holding it partially open. Once the wax sets in the thermostat it is locked in position untill it is allowed to open once again. The fact that it's partially open means that the water temp can never now get hot enough to open the thermostat once more.
So simply by resricting the top radiator hose with the engine running & fans disconnected, it's possible at fast idle to allow the water temp to get to above 90 degrees (mine reached 95). The internal temp gauge at this point was about half way.
The thermostat now has fully opened and perhaps whatever caused the closing problem last time has cleared itself.
I removed the restriction in the top hose and drove the vehicle around for a test drive.
Positive results - Water temp is now about 85 Degrees and heater is as I would expect.
Time will tell whether this is a long term fix or the thermostat will jam again but for the 15 minutes or so to crush the top hose and rev the engine, it's probably a worthwhile test for you to try if you've got a similar problem.
Reading around the subject on the forums, the following points were noted.
1. Access to thermostat is a long job which requires removal of water pump (although there are reports to the contrary).
2. Don't be fooled by the electric radiator fans running whilst undertemperature. The engine fans come on whenever the A/C comes on and the A/C comes on whenever the heater control knob is in the demist (windscreen) or windscreen/footwell position and the cabin booster fan knob is on (1,2,3,or 4) - This fact is irrespective of the main A/C button - The A/C is comes on to aid demisting and cannot be overidden.
So after altering the heater to prevent A/C & fans coming on, I tried again, this time reaching only about 72 degrees, it was still running cool.
I really did not want the hassle of changing the thermostat but also wanted a toasty cabin for the cold months ahead.
Then I had an idea, what if I could force the water temperature above the opening temperature of the thermostat (about 85 degrees), maybe there was a piece of crud stuck in the thermostat when it last closed (or perhaps it closed incorrectly mechanically) therby holding it partially open. Once the wax sets in the thermostat it is locked in position untill it is allowed to open once again. The fact that it's partially open means that the water temp can never now get hot enough to open the thermostat once more.
So simply by resricting the top radiator hose with the engine running & fans disconnected, it's possible at fast idle to allow the water temp to get to above 90 degrees (mine reached 95). The internal temp gauge at this point was about half way.
The thermostat now has fully opened and perhaps whatever caused the closing problem last time has cleared itself.
I removed the restriction in the top hose and drove the vehicle around for a test drive.
Positive results - Water temp is now about 85 Degrees and heater is as I would expect.
Time will tell whether this is a long term fix or the thermostat will jam again but for the 15 minutes or so to crush the top hose and rev the engine, it's probably a worthwhile test for you to try if you've got a similar problem.