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Help please gents!

My 300tdi Disco has developed a strange fault... the heater has suddendly gone cold! It has been fine since i have owned the old girl, yet after a pay and play day last weekend the heater has suddenly gone cold.


The left hand outlet (or inlet) pipe from the heater matrix that goes directly into the top of the head is hot, the right hand pipe which connects from the heater matrix to the metal pipe that goes to the front of the engine then connects to the bottom radiator hose is cold (standing in front of car).

When im driving i occasionally hear a poping sound from the heater matrix area in the dash, to me sounds like an air lock, but the water level has not droped, i have tried to let it bleed itself by leaving the expansion tank cap of overnight but no change.

I have drained the system and refilled...no change

There doesn't seem to be excess pressure in any of the water pipes

When i rev the engine with the expansion tank cap off the water level rises slightly the falls when i back off.

There are no bubbles in the expansion tank

Cylinder leakage tester shows no exhaust gases in the water

No cream cheese on oil filer cap or on dipstick

Engine runs fine

New radiator,water pump, expansion tank, thermostat, p gasket, and water pump 6 months ago

Pacet electric fan

No white smoke out of exhaust.

Could it be a blocked heater matrix????

Any ideas greatly recieved as im pulling my hair out

Thanks for you time reading this essay!!

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Once the engine is up to temperature both hoses should be hot - regardless of the heater switch setting on the dashboard. Try back flushing through the core with a garden hose. Any air in the system may well end-up in the heater matrix and restrict or stop air circulating through it. Unusual for a TDi engine - they usually self-bleed any air out of the system.


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Flushed out matrix, water flows straight through so can see it having a blockage.

Took the water pump off and replaced it with a new spare one, filled up the system again, and still onlt the left pipe getting hot.

Could be imagining it but the pipes seem to be pressurising a bit more now.

Any further ideas.. got me completley stumped, wanted to go to Broxhead on Monday but dont want to risk it if i cant solve this!!!!!!!! :(

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Try disconnecting the 'cold' hose whilst the engine is running to see what happens.

try raising the front of the car to see if its an air bubble in the heater matrix

try disconnecting the 'hot' host from the engine to see what happens

Its got to be either a water flow restriction somewhere, or an air bubble I would have thought.

It may be that on the pay & lay day the car was inclined up or down a steep enough gradient to dislodge either an air bubble or some blockage??

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Thanks Steve, think ive found it!

Did as you sugested and disconnected cold and hot pipes and there seemed to be very little flow either in or out!

Put garden hose on to block and got good flow put on bypass pipe and got good flow, so seemed when engine was running there was poor flow, took new water pump off and checked all looked ok , impeller was fine no play etc, just about to put it back on when i noticed that te impeller was about 10mm away from the pump casting, had a look in the pump housing on the engine and could see where it had been rubbing, looked at other pump i took out on friday and impeller again was away from pump casing!

Took a trip round the corner to local car spares and luckily that ahd a water pump on the shelf, compared it to my two and low and behold the imeller was about 2 mm from the pump casing!!!!

Parted with some cash fit new pump and low and behold heater worked perfectly!!!

Moral of this is dont buy water pumps of ebay!!!! though it was a bargain buying two for the price of one, but two carp ones and hours of head scratching dont make a happy bunny.

Will invest in one of the ones from island4x4 with the better cast impeller next week.

Thanks for all the replys, hope this helps someone else in the future and beware of cheep ebay carp! :rolleyes:

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Glad its sorted - & good detective work checking that impeller clearance, bloomin' pattern parts strike again!

I wonder how many other owners have done this and just put up with poor heater - and ultimately poor cooling in extreme conditions.

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