Hi,

I am new to the forums on here, and am by no means a mechanic, so any replies would be appreciated in laymans terms hehe (I am a lady after all, and relatively new to the underneath of a bonnet).

My 1996 discovery 300tdi started blowing cold air from the heaters when they were set to hot. Initially I thought that there was no water in the system, but the header tank showed normal level when I checked it. I was at a loss as to why this was happening for a week or so, the heaters would sometimes blow hot, but then go cold. Eventually I realised that I was loosing coolant and the water pump began making a kind of "dry bearing" sound.

Sure enough the water pump and gasket had failed. I bought a water pump, gasket, antifreeze and blue gasket sealer, and my friend proceeded to take the water pump off to put the new one on. The gasket had previously been superglued on, and it took him ages to get it off and get a good seal again for the new gasket and pump. Anyway we bled the system using the radiator plug, thermostat housing plug technique and left it overnight to cool down. This seemed to do the trick, once my husband had filled the header tank to the correct level with water this morning. We ran it for over an hour, driving round locally, heaters blew hot and temp gauge stayed just below half as normal. The only thing different was that when we stopped the temp gauge dropped slightly and then when we set off it would rise again to just below the halfway mark. But just as we got excited thinking we had solved the problem, the heaters went cold again!!!!! The engine is not over heating, however the pipe that runs from the thermostat housing to the rad is cold, until the rad cap is taken off then it seems to fill with warm water.

Little bit confused as to whether this is still an air lock or rad problems, or thermostat problems. Praying that it is not head gasket (no smoke, and oil filler cap is fine!!!). The only other thing we noticed about the coolant in the car when we have checked was that it was a very rusty colour!!!

Please please can someone help, or point me in the right direction as to what I can do!!

Thank you (and sorry for the long post, just wanted to be thorough)

check after running it that all hoses are hot and expansion tank is hot also check that the thermostat bypass hose is not blocked that rust coloured stuff can block the valve at the middle of those hoses and screw the water pump up again and check the 2 hoses going into the bulkhead are hot when you run the disco again keep heaters up on hot also check to see if carpet is wet in footwell as heater matrix can leak on these motors. you could try a rad flush toget rid of the dirty water

The bypass pipe from the thermostat housing to the rad stays cold, as does the header tank after running. The pipes that go over the bulk head are not particularly warm, but the pipe that goes from the rad to the water pump is hot. Forgot to mention as well, it seems to have developed a squeak around the pulleys for the fan belt and pas (I think thats what these are), although this sounds totally different from the noise that the water pump developed when it was on it's way out!
My hubby is totally draining the system as we speak. With regards the rad flush, can I do that with normal water, or do i need to buy the actual rad flush fluid to do it!!!
I have toyed with the fact that the termostat wasn't working correctly but the car doesn't overheat now!!! I do feel like there could be a blockage in the pipes at the thermostat housing though.
Thanks for your response. I have read so many threads on this problem, but they all seem to have the motor overheating, and mine isn't!

viks3457 said:

The bypass pipe from the thermostat housing to the rad stays cold, as does the header tank after running. The pipes that go over the bulk head are not particularly warm, but the pipe that goes from the rad to the water pump is hot. Forgot to mention as well, it seems to have developed a squeak around the pulleys for the fan belt and pas (I think thats what these are), although this sounds totally different from the noise that the water pump developed when it was on it's way out!
My hubby is totally draining the system as we speak. With regards the rad flush, can I do that with normal water, or do i need to buy the actual rad flush fluid to do it!!!
I have toyed with the fact that the termostat wasn't working correctly but the car doesn't overheat now!!! I do feel like there could be a blockage in the pipes at the thermostat housing though.
Thanks for your response. I have read so many threads on this problem, but they all seem to have the motor overheating, and mine isn't!

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I don't think from what you describe that you have any major problems.
300tdi heaters can be very difficult to bleed properly.
After you have flushed the system, water will do, fill the system with water and antifreeze as you did before and then gio and have a run in the car. When you come back let the engine cool and then check the coolant level again, it will probably have dropped a bit. This just air in the system-it takes a little while to collect at the top. Go for another run.
Let the engine cool again but this time undo the heater flow connection off the top of the cylinder head. This is the pipe that rises vertically off the head at the back, not the metal pipe running along the top of the head.
Hold the rubber pipe up vertically and get someone to put their thumb over the pipe connection on the head.
With a jug fill the vertical pipe slowly until its overflowing and then quickly put the pipe back on the head connection and tighten the jubilee clip.
Your heater should now be vented and full of water. The heater should now work(!)
Keep checking the coolant level for a couple of days just to make sure all the air is out.
Best of luck.

nicedayforit said:

I don't think from what you describe that you have any major problems.
300tdi heaters can be very difficult to bleed properly.
After you have flushed the system, water will do, fill the system with water and antifreeze as you did before and then gio and have a run in the car. When you come back let the engine cool and then check the coolant level again, it will probably have dropped a bit. This just air in the system-it takes a little while to collect at the top. Go for another run.
Let the engine cool again but this time undo the heater flow connection off the top of the cylinder head. This is the pipe that rises vertically off the head at the back, not the metal pipe running along the top of the head.
Hold the rubber pipe up vertically and get someone to put their thumb over the pipe connection on the head.
With a jug fill the vertical pipe slowly until its overflowing and then quickly put the pipe back on the head connection and tighten the jubilee clip.
Your heater should now be vented and full of water. The heater should now work(!)
Keep checking the coolant level for a couple of days just to make sure all the air is out.
Best of luck.

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Thank you very very much, I love laymans terms and you description is very easy to understand. Hubby has flushed rad with water and sure enough loads of "bits" came out. Put it all back together and filled up again. Left it sat idling for a few minutes with header cap off and then he's going to go for a run in it then check coolant. Thanks again and I will post once I have done the heater pipe venting as you have suggested. Thanks again

HI, just a quick update.
The thermostat appears to be a problem. We have bled the system, but the pipe from the thermostat housing to the rad is still cold. Took the stat out, dropped into boiling water - nothing!!!!
Could this be the problem??
Thanks

viks3457 said:

HI, just a quick update.
The thermostat appears to be a problem. We have bled the system, but the pipe from the thermostat housing to the rad is still cold. Took the stat out, dropped into boiling water - nothing!!!!
Could this be the problem??
Thanks

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The chances are your thermostat may be faulty due to the age of your car, while you have it out you might as well replace it for what they cost.
Unfortunately it has no bearing on your heater problem. The pipe from the thermostat housing to the top of the radiator probably is cold, it simply means the thermostat hasn't opened for what ever reason. 300tdi's are vastly over cooled such that the radiator rarely comes into play in cool/cold weather. My radiator is almost never used .
If your thermostat housing is hot, check to see if the metal pipe running along the top of the head is also hot.
If it is you have water circulation thro the heater, if not you still have an airlock, or the heater matrix is blocked with debris. They can block.
When did the heater last operate?

nicedayforit said:

The chances are your thermostat may be faulty due to the age of your car, while you have it out you might as well replace it for what they cost.
Unfortunately it has no bearing on your heater problem. The pipe from the thermostat housing to the top of the radiator probably is cold, it simply means the thermostat hasn't opened for what ever reason. 300tdi's are vastly over cooled such that the radiator rarely comes into play in cool/cold weather. My radiator is almost never used .
If your thermostat housing is hot, check to see if the metal pipe running along the top of the head is also hot.
If it is you have water circulation thro the heater, if not you still have an airlock, or the heater matrix is blocked with debris. They can block.
When did the heater last operate?

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It last operated fully for over an hour yesterday but this morning it only got luke warm after about quarter of an hour of running but then went cold again.
Thermostat has been replaced. There was no movement at all in the thermostat when I dropped it in to the hot water.
Unfortunately the water pump seems to be squeaking again now. This does come and go this noise though?????
Sorry to seem a bit vague!
Thanks

Hi,
Just another quick update - new thermostat fitted and the pipes are now hot - the only one that isn't is the metal pipe that runs to the heater matrix - so we are going to let it cool and then do the pipe removal on the back of the head, and fill it up with water.
Hopefully this will solve the heater issue.
The odd squeaking noise is still there though.
Wasn't there before water pump was changed!!!!
Thanks

Just another quick update - filled the pipe that rises vertically off the back of the head with water (as my hubby had his thumb on the bit I took it off). Put it back on very quickly, and low and behold, the heaters are still cold!!!!!! lol
That pipe that we filled up is getting hot, but the one that runs from the metal pipe on top of the head is cold!!! Any ideas??
Thanks

Hi, can't offer any words of wisdom on your heater problem but the odd squeak issue might be the fan belt. They often make noises that has been described as sounding like "a box of budgies".

When it's squeaking spray a small squirt of wd40 onto the alternator pulley, (taking care not to get anything caught in the moving belt of course!). If the squeak instantly disappears, it's the belt. It'll start squeaking again a couple of minutes later.

If it is the belt you need to do the penny trick. It's dead easy to do and works a treat. Do a search on here for it, there's pictures that show where to insert the penny.

viks3457 said:

Just another quick update - filled the pipe that rises vertically off the back of the head with water (as my hubby had his thumb on the bit I took it off). Put it back on very quickly, and low and behold, the heaters are still cold!!!!!! lol
That pipe that we filled up is getting hot, but the one that runs from the metal pipe on top of the head is cold!!! Any ideas??
Thanks

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Thats disappointing. Given that you said the heater worked a few days ago I can only guess you still have an air lock.
What I would now do is to undo the pipe at the top of the head as before and connect a garden hose to the metal upstand pipe and leave the rubber hose open and turn the hose on until water comes out of the rubber hose in a constant stream. Shouldn't take much. Then refill and reassemble as before.
If this works you will need to add a bit more antifreeze to the coolant as you will have diluted it a little.
Lets know how you get on.

nicedayforit said:

I can only guess you still have an air lock.

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I wonder if some debris has been dsitrubed and the heater matrix is now blocked? May be it needs back flushing...

I am fairly sure that I have an airlock somewhere. I have back flushed the heater matrix to no avail. SO I have bypassed it for now. Thought I had sorted the problem all the pipes got hot. Then low and behold, car sat idling for over 2 hours no overheating at all, then the gauge began to rise when we took it out for run. Got it home (we were only 30 secs away from home and the guage had almost reached 3/4, and the thermostat housing again was dry!! We are just going outside now to begin to try to bleed the system again!!!!!! No coolant loss at all (until of course we drain it hehe). I am really tempted to drain the full system AGAIN!!!!!!
However can I just pick brains, where the pipe runs from the water pump over the top of the engine (through the metal pipe) and then into the heater matrix, which side of the heater matrix does that pipe go onto!! Sorry for the bad description but it looks to us like the inlet goes into the heater matrix on the pipe on the right and then the one on the left brings in out and goes back into the engine!!! Would that be right??
What I have also noticed is that the metal pipe that runs across the top of the engine is also the same level as the thermostat housing, so I think air is rising to that point instead of the termostat housing. Anyway I can overcome this??
Thanks
Vikki

Sounds like an air lock, Run the engine for a while with the header tank cap off

viks3457 said:

However can I just pick brains, where the pipe runs from the water pump over the top of the engine (through the metal pipe) and then into the heater matrix, which side of the heater matrix does that pipe go onto!! Sorry for the bad description but it looks to us like the inlet goes into the heater matrix on the pipe on the right and then the one on the left brings in out and goes back into the engine!!! Would that be right??

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Having fun aren't we?

The above is correct, The flow connection to the heater rises off the back top of the head, the return connection is the metal pipe that runs on top of the head and connects with the suction side of the water pump.The heater matrix is only a pipe coil with fins on it.
I tend to agree that you have an air lock /blockage in the metal return pipe.
The only way I can think of to clear this is to fill the rubber flow pipe as before , thumb etc, but this time undo the rubber hose from the front of the metal pipe seal the rubber hose with a cork etc or clamp it and the fill the heater flow hose as before. When the heater circuit is full water should pour out of the end of the metal pipe ie its full of water. Refit hose to end of metal pipe and finish filling rubber flow hose and refit. If this don't work you are pulling fresh air into the coolant system. Check the connections on the inlet side of the pump, the hose from the bottom of the radiator. Although it may not leak coolant air can get sucked in when the pump runs.

Can you park on a slope, with the front of the car pointing up slightly, when you bleed it? Might help

I had the same problem on my 300 tdi turned out to be a dodgy thermostat, have you checked the new one is working, could be a faulty part.

i took the hoses off the bypass the other day and found it blocked with brown gunk from old header tank i put on a t-piece connector and working fine but i think it nackerd my old water pump and thermostat so i will check it when i service the motor

Hi

I had exactly the same problem as your experiencing and i tried everything that you have done.
The one other problem that i had which i dont think you have is when it got hot it (sometimes) spilled water out from the header tank.
I tried thermostats, bleeding, pressure tests, block tests etc etc and they all seemed to come out ok.

I finally decided to take the head off to find the gasket seemed ok, so i took the head to a specialist and he found that the head was warped.

I had it pressure tested and skimmed and iv fitted it back on and all seems OK now.....TOUCH WOOD!!

Sorry to give you the bad news but it may solve your problem

Hope you get it sorted