Help please!!!!

Right i have a 300tdi disco 97 plate with 160k miles on the clock.
I am having an irregular fluctuation of the temp gauge, it will stay fine for days then it will rise towards the overheat mark but never gets to the top.
If i take my foot off the gas for a bit the needle drops back down, same up hill with high revs.
Also i am struggling to get any heat from the heater it just blows very mild.
I have changed the coolant, top hose, thermostat.
I took it to a mates garage where i was told its the Impeller in the pump not working properly, yet the guy i took it in Swanseavale4x4 said if there is no heat in the cabin then the heads gone.

I bled the system last night the way swanseavale told me took it for a run and had loads of nice heat blasting out of the heater, also i gave it some welly and the needle didnt budge off a third.

Yet today i am back to mild warmth from the heaters.
I am stumped.....

coolent leak causing an air lock?
head gasket?

Rather stupidly i have forgotten to check if the hoses going into the heater matrix are actually hot or if there is a blockage before them.
Will give it a try tomorrow.

try and run the engine upto temp an when you park up lay a large sheet of cardboard under the engine bay to see if a hose is leaking and dripping to the floor after the engine cools slightly, mine did that when the water pump p gasket went,
if you don't find a leak that way then ya H/G fooked.
good luck mate!

Clutching at straws and in a vain attempt at being positive i was told the water pump was changed before i bought it.
Hopefully they did it wrong at fooked the p gasket.

Got it up to temp this morning on way to work, left engine running and checked coolant level, that was bang on.
Did the cardboard test, no drips.
Undid the bleed screw, the coolant bubled up nicely.
Checked the pipes going into the matrix, they were cold and empty.
I presume there is a blockage there somewhere.
Will be getting it tested for gasket failure this afternoon at my nephews garage, fingers crossed.

I must have done something right this morning as it is now pumping out lots of hot air, i gave it some high rev welly earlier and the temp gauge is rock solid on the one third mark.
:clap2:

hope thats it sorted for you then mate, they can be a bastid when they get air locked!
my brother in law can vouch for that, took him weeks to get rid of the air in his disco

Well i had it confirmed today by 2 different garages, head gasket on its way out, both quoted around the 600 mark.
Does that sound about right, the first was from Swanseavale 4x4 and the second and the one i may go with was Autec.
I was informed that the guys from Autec are the best in swansea with diesel engines.
I could phone around all day tomorrow to bring the price down, but i want it done once, not again in 6 months time by a professional.

The 600 is for strip down, pressure test, skimming, full clean and re-build and new oil/filter and coolant.
Was gonna be cheeky and ask for the timing belt aswell as its in bits.

i dont understand how your engine can be running fine but need a new head gasket? surly when there gone the engine goes up in steam and you also smell coolent in the zorst or get oil in the coolant!!

With Paul on that... you have a cooling system issue with no loss of coolant. If the coolant ain't going nowhere it can't be a head gasket.

i hear people all the time saying that heating problems are related to the head gasket. i have a heating broblem that only occures on the motor way any other time is ok and i hardly ever neet to put the electric fan on. but the head gasket cant cause my over heating the engine is in good nik and pulls like a train.

The heating and coolant problem is fixed, its just that all the overheating has ****ed the gasket up, its blowing coolant out of the exhaust system and i am losing water, there are no drips from anywhere in the engine so it has to be through the head.