Running cold

[grahamjf]

Hi all

My car runs cold very seldom the car gets above 50 degrees unless it's getting booted up a hill then drops back to the 50 again.
Changed the thermostat to a 88 degrees still the same running cold.
Plugged in live data temperature gauge reads correct when I drive watching the data screen I can see the temperature rising going up a hill and dropping back going down a hill.
When i do a diagnostic check on it comes up with engine coolant temperature sensor changed that for a genuine audi one cleared the codes still comes up with that fault
Took the thermostat out, put it in a jar of boiling water at 88 degrees, I can then see it opening. Poured in some cold water it closes.
No mental black smoke, the heaters good but not mental hot, some times I get 53mpg some times as low as 40mpg all under the same driving conditions.

Top and bottom radiator hoses dont get too hot and the hoses going to the internal heater are not hot (just warm)

Any ideas on this one? I'm totally lost

2005 Audi A4 B7 2.0 tdi

[Trevor]

Could only imagine that there is some air in the system....possibly a bleed point in the heater area?

[grahamjf]

Pulled back the hose at the heater. There was a flow of coolant then a pause then flowed again.

[Trevor]

sounds like there was air in the system then...or a slight blockage?

[grahamjf]

took the car for a 30 minute run temperature still at 50 (cold) Heater warm.
Got back home left the car running took the hose of at the heater matrix with the pin hole. Put the heaters to hottest setting and full speed
Ran the car for ten minutes no sign of any water coming out of that hole or bubbles, Took the expansion tank of and lifted it as high as it would go for 5 minutes still no water.
Switched the car off took the cap off the expansion bottle and after about two seconds there was a good flow of water came out.

Is my water pump gone?

Top of the engine is not hot, you can put your hand on it

Any help on this i'm lost

[Trevor]

It could be the water pump but with the thermosyphon principle of coolant circulation within the engine, it should still circulate coolant to the top of the engine.

The only other thing to do would be to backflush the cooling system by running a hose through it in the opposite direction to normal flow....that'll flush out any crap in there.

[grahamjf]

Thanks for the reply

How do I go about a backflush?

Wouldn't a blockage in the cooling system cause the car to overheat?

[Magnet]

Hello Graham,

Not sure how much of this is going to be helpful since you seem to have covered most of what would be seemed logical to cover, so it may be time to further question the way in which you have done things. Apologies if this appears pedantic but this is what I would do I terms if rechecks:- 

With coolant at cold, turn the heater control to max. hot and drain the system (collecting the coolant if you can). Remove the thermostat and place in very hot water on the stove, and continue to heat the water until the thermostat is open. Carefully remove the thermostat from the water with a long nose pliers and insert a length of cotton between the body and the open valve (be quick!) The valve will now close and jam the cotton, and you can suspend the thermostat by the cotton thread. Armed with an accurate thermometer, gradually reheat the water - with stirring- and note the temperature at which the thermostat falls from its suspended cotton. This should be 88c or very near to this. Simply placing it in boiling water and making sure it opens and then adding cold water to make sure it closes is not accurate enough, You need to actually measure the temperature at which it opens, and assure youself it is 88. 

When the system is refilled, as you know, you will need to squeeze the hoses to eliminate as much air as possible and then bleed the remaining air via the bleed screws. I don't replace the reservoir cap at this stage, but start the engine and allow the coolant to rise until the thermostat opens and the top hose gets warm, at which stage I replace the cap and allow the engine to run until the fan cuts in - keeping an eye on the temperature gauge. Obviously making sure fingers and fan are kept well apart, I continue to squeeze the hoses, particularly the heater hoses which should now both be at the same hot temperature. Leave the car to thoroughly cool without slackening the cap. Top up when cold and road test the car with the heater still at hot.

If the thermostat passes the correct opening temperature test and the coolant temperature still fluctuates then it's head scratching time again!

Water pump faulty? Not had one do that yet and obviously  agree with Trevor. 

Probably a lot of rambling and maybe not a lot of help, but...

Kind regards,

Gareth.

 

[grahamjf]

Thanks for the reply

 

I'll give it a try.

[grahamjf]

Took the car out today for a 30 minute drive, With the engine running pulled back the bleeder hose on the heater matrix and a good flow of coolant came out straight away. No sign of any air.