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300 TDi Auto Overheating Problem

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After a week and half of my 1996 2.5 TDi Automatic Discovery being off the road due to gearbox oil problems I finally got my Discovery back on the road and in use.

While it was parked up it had a new radiator and pipes fitted along with a new thermostat.

I test drove it when it was first fitted when we thought we had solved the gearbox problem and the temperature gauge went up to 3 quarters and dropped back down to half way.

Today I drove 6 miles and wasn't watching the temperature gauge (stupidly I know), and as I was pulling into a parking space I noticed my temperature gauge was literally 1mm or less below the red marker. So I turned the engine straight off and found that the water had pressurised in the expansion tank. I waited half an hour before starting the 6 mile journey home, At first if the revs stayed below 1500rpm and the speed was 30 or lower the temperature stayed at half way, then as soon as I picked speed up the temperature gauge shot up. It did this twice. Both times I stopped before the gauge read above the top white line. After that I tried going slow and it made no difference anymore, I had to stop 1 more time and wait a few minutes and then got it home.

What could this be? My other half and I are spending the afternoon servicing it anyway, so would like to try and sort this out.

There is no signs of water mixing with the oil.

Cheers

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The thermostat is brand new, but I suppose it could be faulty. I may have an air lock. I really need it to not be the head gasket.

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Thermostat checked, I have bled the system thoroughly, the car is still over heating. I think it is safe to say the head gasket has failed.

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Only smoke when it's running is a tiny but of black smoke, and I mean tiny, otherwise it doesn't smoke at all. I will pop out and do what you said Landy-Novice and see if there is any bubbles and come back with the results.

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Is the water pump run on the Cambelt or Fanbelt?

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I'm wondering water pump...

or iffy thermostat.

Just because it is new doesn't mean it works.

When it's "hot", is the top hose & radiator hot?

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My new fan belt had ATF spilt on it when the mobile mechanic was topping the gearbox oil up, I am wondering if the belt is slipping. I agree totally about the thermostat, but at the same time I haven't had the water pump replaced, it was supposedly done by the guy I got it from. So it may well need a new water pump.

I have gone as far as I physically can with the car, I have made myself very ill today and am now unable to walk at all despite all the medication. So Monday, I am going to have to pay a garage to diagnose it for me.

I was hoping that bleeding the system would solve it..

Thank you for all your help though. I will right on here exactly what it was that is found to be at fault. I am looking to get the car into a garage Monday or Tuesday if I am lucky.

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Yes the top radiator hose and radiator were hot when the engine was hot.

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stupid question incoming....

since the new radiator, it has been filled with coolant, not just water?

if your not sure, you can test it putting a tiny bit on your tongue, if its sweet, it has antifreeze. (thats how i was told to in college. :) )

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At the moment it has roughly 50/50 mix of Anti Freeze and Water. I would never put just water in a coolant system. The Antifreeze can be diluted to 1 part coolant and 3 parts water.

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At the moment it has roughly 50/50 mix of Anti Freeze and Water. I would never put just water in a coolant system. The Antifreeze can be diluted to 1 part coolant and 3 parts water.

ah, thats good. but was it ready to add or concentrated? (not questioning your ability! just an easy mistake to make and eliminating an easy to rectify issue to help find the issue)

and yeah, giving a 25% mix (far from optimum) and if adding to much will cause engine to run hot as well...

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You say on first drive the gauge went to 3/4 then dropped back - thermostat could be 'lazy' in that its slow to open and could have got slower .

One good check I found was the heater output - airlocks tend to cause intermittent output from heater . Once engine has warmed up and heater is putting out hot/warm air it should continue to do so . if heat output fluctuates without any action on your part then you could still have an airlock .

Another simple check I found was that

a) with engine hot hoses are fairly rigid/solid due to increased pressure ;

b) when engine is fully cooled down hoses should soften BUT if a failed headgasket is causing the problem the hoses tend to stay

rigid/solid even with engine cold . Not very scientific method :closedeyes: but I found it to be an indicator .

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It was Concentrate. And no fluctuation in the heating. It is cold all the time. Never gets warm at all.

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If heater does not at least get warm then I would suggest you still have an airlock. Check the 2 hoses that go from the engine bay into the heater - see are both getting warm .

You will probably find that only one is getting warm which means the coolant is not circulating through the heater matrix . And if there is air in there it will expand as things warm up and over pressurise .

there .

The heater can be difficult to bleed and there is plenty of info available - just Google 'bleeding 300 Tdi cooling system' or something similar . This is one link but there are many others :

http://www.devon4x4.com/index.php?option=com_kunena&id=29309&catid=5&Itemid=106&view=topic

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Does this mean I need to drain the entire system and start again? As I would be tempted to fill the heater matrix directly through one of the pipes and then fill the rest of the system afterwards. Is it worth me getting another thermostat to be on the safe side?

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No you wouldn't have to drain the system - your aim is to get coolant flowing through the heater .

You could disconnect the pipe thats remaining cold and try to get coolant to flow through it and then reconnect .

Squeezing the top and bottom hoses along their length can also help as you assist the flow of coolant - just be careful if the pipes are hot .

As you squeeze the hoses you may notice some movement in the expansion tank ; sometimes if you top it up to full and just leave it for a while with cap off the coolant may slowly displace the air .

If you spend a while on Google as I said there is a wealth of information on this subject - and you will also see that it is a common problem.

As regards thermostat you could take it out and test it . Suspend it with a piece of thread or string in a saucepan of water . As the water nears boiling point the thermostat should open .

If it checks out then concentrate on bleeding the system

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I will see how I feel tomorrow and how the weather is. I might try the trick where you blow into the expansion tank to bleed up to the thermostat on the heater matrix pipes.

Just to confirm, is one of the heater matrix pipes the one that does directly into the top of the engine passing from the left to the middle by the rear rocker cover bolt?

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try taking the thermostat out and take it for a little drive, that will eliminate thermostat problems

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Just a thought, but you do have the thermostat installed the right way up with the air bleed hole at the top, and if your's doesnt have an air bleed (some I've seen dont have one) drill one in - around 3mm dia and position it at the top

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Yeah, mine is the right way round with the bleed thing on top.

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