Help Please! Coolant problems following water pump and thermostat change

[4WheelDrifter]

I always leave the cap off to start with too. But the system won't pressurise, so the fan may not kick in.
Make sure you take a bottle of coolant on the first drive too, just in case.

[Error404]

Steve its not uncommon for new stats to not work correctly - I always test mine in hot water before fitting to be sure.

Before you strip it all out to change the stat, you can do a few things though to be sure.
Run the engine from cold with the cap off the expansion tank until it starts to overflow then replace the cap.
Bleed off any air in the matrix but pulling IIRC the left hand hose (the one that leads to the head) carefully back to allow a tiny gap for any air to escape. (The B5 and later matrix pipes have a small hole near the end for this purpose.)
Lift the expansion tank a few inches and open the bleed screw on the rad to allow any air to escape there also.
Once no more air comes out, you should be bled properly - keeing an eye on the temp gauge take a cautious drive for a few minutes on some very local roads to get the water pump spinning at a decent rate to circulate coolant through the system. Then allow the car to cool down and check and adjust the coolant level.

If that doesn't work then I would feel confident you have a bad thermostat.

HTH

[benntenn67]

I would say thermostat, either faulty or incorrectly fitted, the thermostat on my 5 cyl passat had an arrow stamped into it - to show the position it should be fiited - that must be for a reason (function, airlock etc)

[Fat Audi 80]

Thanks again chaps. I will let you know how I get on once I get some time again...

[Fat Audi 80]

Sucess! I didn't do a lot differently tonight. Well, I did loosen the inlet hose to the heater matrix to try and bleed that, I loosened the bleed screw on the top of the rad and lifted the expansion bottle a little higher. The thermostat seemed to eventually open and I have coolant flowing around the entire system.

A shake down run has shown the car to remain steady at temperature and the fan kicks in at speed one normally. My only remaining minor issue (which didn't help the initial bleeding process is the temperature gauge sits at 1.5 - 2 notches ABOVE 90 and the fan kicks in at 3 notches above 90 deg. I am not seriously concerned about this as I have just fitted a new MFTS which provides this signal and the fan is kicking in exactly the as it did previously.

Has anyone else changed the MFTS and had a significant change of dash temps? Incidentally, the old MFTS is 4 pin, the new on 3 pin, is this correct?

Generally though I am over the moon to have the car back working properly and chuffed that I have completed it all myself.

Thanks for all the help and words of encouragement.... TOP FORUM.

[Monkeymagic]

the new switch is 3 pin as the extra earth has been removed. not sure about readings though.
i have an infra red thermometer as you can't always trust the readings given on old cars.
the Thermo gives very accurate readings

[AndyP]

Everybody I know who has fitted one of the new 3pins MFTS, be it dealer or aftermarket, has said they over read so I wouldn't worry about it.

[Fat Audi 80]

Everybody I know who has fitted one of the new 3pins MFTS, be it dealer or aftermarket, has said they over read so I wouldn't worry about it.

As I suspected. Thanks Andy.