disco heating problem,help please

hi guys,ive looked through previous posts concerning heating,but cant really find anything that satisfies my question,probably there somewhere...
bought this car in september,with the recent cold weather its become apparent that the heaters werent working properly and gauge slow to move,so i bought a new thermostat,after removeing the stat housing to replace it,it didnt have a stat in.since putting one in(wednesday)its toasty warm,but the temp gauge is off the map,goes up as far as it can past the red,i got home tonight from work,a 10 mile journey,and checked the rad top hose and it was cold,and the fan was on,but needle on gauge was skyward,does this mean ive got air in the system,if it helps its had the HG and waterpump replaced,so im lost............

DAZ

Faulty Temp Sender?

Sounds like u got a blockage some where or trapped air flush the cooling system and refill it with correct mix of antifreeze and quick oh and make sure you bleed it up properly this time. apart from that some one else will be along shortly to say I'm wrong and give u some more idea's

Sounds like an air lock, bleed the system n all should be good

Sounds like you got air mate, fill expansion tank and remove it from holder, hold the tank about 4 inches higher than the top hose and open the bleed screw, make sure plenty of water comes out to remove all the air, then run it up and just slacken the bleed screw to make sure no air is in system, put the cap on, job done

If you're bleeding for an air lock, might as well bung a new sender in too?

thanks guys,really appreciate all your help,ill do that,thanks again....

DAZ

ive bled the system as instructed,but i dont seem to be able to feel water in the top hose,and the top hose stays cold to luke warm,aarrrrgh.

you say top hose is cold, what about the radiator if thats cold, maybe its blocked, try removing top and bottom hose from rad and running water through it, ie with a hose pipe the water should flow through the rad easy, maybe thats why there was no stat in, there before could also be the reason for hg going in the first place

thanks mate ill try that,just to note,the fan is on constantly,not just when it needs to be??..........

the viscous fan will be on all the time so dont worry too much about that bit.

there is a thread on here somewhere explaining how they work and you will find there are quite a few folk who do away with them completely.

ok guys,i did everything you advised,its all been ok till last night,the gauge is skyward again,i noticed today the gauge was half way,then when i put my lights on it flew up,turned lights off and it came back down,if i use wipers or indicators the gauge fluctuates virtually in time with wipers or indicators,without sounding stupid,this indicates an electrical fault,but where do i start looking,again,many thanks for all your help so far,thinking about getting rid now,doing my head in although im hoping its something simple................

You've got an earth fault somewhere.
I'd start with the main body earth just behind the battery, looks like a cable clamp.
Take it to bits, clean all surfaces to bright metal, give the surfaces a coat of vaseline and re-assemble.
Which model of car by the way.

its a disco 300tdi mate,thanks for your reply...

ive just disconnected the sener unit and the temp dropped to cold,could this be the problem or still something more sinister?

By disconnecting the temp sensor you've just made the gauge drop to zero.
You've still got an earth problem.

ok mate ,thanks again,but also in the manual it says run to operating temp,then disconnect sensor,if gauge falls the sensor is dodgy???

dont seem to be able to find main body earth,ill check again...

problem now sorted guys,you were right it was an earth fault,i couldnt reach the main body earth without taking rad out,so fitted another earth strap,seems ok now,fingers crossed,thanks for all the help...

DAZ