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637Nook

300TDI Overheating problems......

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637Nook    0

Hi Guys,

I wonder if any of you techies out there has any ideas, my brother has a 300tdi its run fine for the past three years apart from blowing the head gasket about 9months ago which was replaced without incident and has been running fine since.

Now to the problem, about 6 weeks ago the belt tensioner on the front of the engine some how loosened itself and came off, this in turn shredded the fan/alternator/water pump belt I managed to get the 90 home without the temp gauge getting anywhere near the red, the tensioner was refitted and a new belt added everything ran fine........or so we thought.....

short hops below 40mph the engine temp stays low, as soon as you do a longer/faster journey the temperature gauge goes up into the red, the internal heaters blow cold while the temp gauge keeps rising....they will then suddenly blow hot and the temp gauge will drop down to normal running temp, after a very short time the blowers go cold and the temp starts going up again!....

My first thought was thermostat, this was replaced with a new one (checked and working before installation), no change.... <_<

Water pump checked, replaced with a new one, no change..... :huh:

Expansion cap replaced (in case the system was not self releasing air properly) no change...... :(

All the hoses removed and water blasted through the system by hose to remove/check for blockages, no change..... :o

We are now running out of ideas and the problem remains.... :blink: !!?

Anyone out there got any ideas or suffered anything serious? the only other thought we have had is that the head gasket has gone again and is over heating/pressuring the system but I thought before we pull the head off i'd ask if anyone has any ideas!?

Cheers Guys

Andy

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western    211

reckon you've covered all the bases, might be worth having the cooling system pressure tested before condeming the head gasket again, at least the results will point you in the right direction or it could be a big airlock.

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Tetsu0san    15

Like western said it could be an airlock, but it sounds like a head gasket to me I'm afraid (or a cracked head) :(

When they did the head gasket before, did you get a replacement head or just the gasket? It could be that the head was OK before but in overheating this time it may have cracked it, especially if you had it skimmed before. 300Tdi's are known for cracking heads (as I found out...)

However, get a pressure test done on the coolant and see if it is rising above the norm while the engine is running.

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637Nook    0

Cheers guys, I'll try and find someone that can pressure test it....

we did the head gasket ourselves as were both pretty good with the spanners, just replaced the gasket, head looked fine and went back on and ran fine for the 9months so far until this problem

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muddy    27

The temp gauge can only give you a coolant reading for the coolant that it is sitting in. Because you had no waterpump drive the water will not have been circulating properly through the cooling system, the coolant in the water jacket around the head could have been twice the heat showing on the gauge and you would not know because the heat will not nessacerily transfer to the area around the sender.

Old cars were engineered to circulate the coolant without a pump hence old cars having very tall radiators with the top hose at the top of the system however the 300 system does not have this and therfore cannot cope without the pump running. I'd say its time to cut you loses and redo the head/head gasket.

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637Nook    0

Cheers Muddy that makes a lot of sense, never thought of that! back to the garage to pull the head off again then.... if its cracked are we liable to be able to physically see it?

Cheers for the advice appreciate there's a lot of experience on here :)

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cackshifter    22

I've discovered if you blow hard(ie by mouth) into the expansion tank you can pressurise the system - if you then release hoses at high points, eg heater, top of thermostat, air followed by coolant emerges, and you can then reconnect the hoses knowing there is no air in. If there is air in the system, you can feel it as springiness when you blow into the tank, and when you stop and look into the tank coolant will be forced back into the tank, presumably as the trapped air expands again. OTOH if there is no air, there is very little springiness or flow back. I obviously can't recommend you do this as ethylene glycol is poisonous, but recently when I was stuck it bled the system a treat, and I only had a faint taste of antifreeze, reminiscent I think of some German wines. Once the air is all out, and the system topped up to the correct level it should be fine. If you get air in again there has to be a fault, head gasket has to be prime suspect then.

Nigel

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bigstevemex    0

just to add a bit more on bleeding systems.i dont recommend doing it with your mouth.if you have a coolant pressure tester you can use that if not try this.get an old plastic drink bottle.cut off base turn upside down.put in radiator or exp bottle neck.seal joint with o ring/tape/silicon,whatever you can find.top up coolant so bottle is half full at least.run engine ensuring heater valve is open.the extra weight of water will often help the air escape and clear the airlocks.the bottle needs to be i.5 or 2 litre size.hope this helps used it many times.

p.s if you think about the cooling system like a radiator in your house the bleed point is at the top.when bleeding your system if you can raise the front of the vehicle(or the side where you are bleeding from)this also helps.

thanks steve

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Davey1000    0

You don't say whether the problem vehicle is a Discovery or a Defender. I'd guess its a Disco as owing to the shape of the bonnet, the header tank is mounted lower than what it (IMHO) ought to be. The nett result is that unless the head, block and gasket all make a 100% perfect hermetic seal, gas will get into the cooling system and create air locks. In actual fact on this design once the engine block temperature exceeds about 110 degrees water will be expelled from it and it will run dry! The high mounted water pump also exacerbates the problem. This is the reason why old Discoveries are so cheap. The viscous coupled fan and in particular the oil cooler in the radiator is IMHO a disaster as this puts all ones eggs in one basket. An oil-to-air heat exchanger is on the other hand invincible and it will continue to remove a good percentage of the engines heat even when the water has gone. One other snag with the 300TDi engine is its petrol ancestry. The middle two exhaust ports are next to one another. With a petrol engine this was done to provide heat for the "hot spot" that was used with down-draught carburettors. Unfortunately having two exhaust ports side by side also creates a hot spot in the cylinder head and it is here where the head gaskets usually fail.

At the time of writing the "going rate" for a bare cylinder head made in South Africa is about £230 and the consensus of opinion is that Discoveries with "cooked" heads usually need a new one. When one considers the cost of skimming the old head and ending up having to do the job twice it is probably better to bite-the-bullet and pay the money.

On my Discovery I hope to raise the header tank even though this will entail creating a bulge in the bonnet.

Good luck!

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Buzza    0

You don't say whether the problem vehicle is a Discovery or a Defender. I'd guess its a Disco as owing to the shape of the bonnet, the header tank is mounted lower than what it (IMHO) ought to be. The nett result is that unless the head, block and gasket all make a 100% perfect hermetic seal, gas will get into the cooling system and create air locks. In actual fact on this design once the engine block temperature exceeds about 110 degrees water will be expelled from it and it will run dry! The high mounted water pump also exacerbates the problem. This is the reason why old Discoveries are so cheap. The viscous coupled fan and in particular the oil cooler in the radiator is IMHO a disaster as this puts all ones eggs in one basket. An oil-to-air heat exchanger is on the other hand invincible and it will continue to remove a good percentage of the engines heat even when the water has gone. One other snag with the 300TDi engine is its petrol ancestry. The middle two exhaust ports are next to one another. With a petrol engine this was done to provide heat for the "hot spot" that was used with down-draught carburettors. Unfortunately having two exhaust ports side by side also creates a hot spot in the cylinder head and it is here where the head gaskets usually fail.

At the time of writing the "going rate" for a bare cylinder head made in South Africa is about £230 and the consensus of opinion is that Discoveries with "cooked" heads usually need a new one. When one considers the cost of skimming the old head and ending up having to do the job twice it is probably better to bite-the-bullet and pay the money.

On my Discovery I hope to raise the header tank even though this will entail creating a bulge in the bonnet.

Good luck!

Erm, its in the Defender Forum, :unsure:

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