Td5 cooling

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Originally Posted by Franksd

Thanks James. On driving it this afternoon I noticed the coolant temp jumped from 83 to 89 then back to 83 in a matter of seconds.

I lifted the bonnet as it jumped back up to 88. The top radiator hose was rock hard. As I removed the expansion tank cap and there was no pressure releases all which is normal for my ute. The coolant level was at the cold level. I could hold my fingers in the coolant so I am guessing it must have been no more than 40 degrees.

About 30 seconds later the top hose went soft and coolant in the expansion tank raised to the usual hot level. It was scolding hot.

Does this sound like a cracked head?

Dan.

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What seems to happen is that pressure builds up at the top hose, the gas/air being lighter than water, but will to some degree self bleed when the pressure builds up too much.

The temp sensor readings jumping around are *probably* due to the sensor probe going from being in coolant to not.

The one thing that would concern me regarding it being a head/head gasket, would be the lack of pressure at the radiator cap.

But the rest sounds like at least a head gasket.
What year is the car? EU2 or EU3?

If it's older it could still have the plastic dowels, the head will shuffle and wreck the head gasket.
I've even seen the plastic dowels being used again (new ones)when the head gasket has been changed, and it will then last another 100 000 km and let go again.

Use the steel even in the early heads although I think the land Rover official docs say you can't in the early ones.

The head will need to be tested for hardness if it is to be reused, as well as cracking/warping.

Cheers
James

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Originally Posted by shack

What seems to happen is that pressure builds up at the top hose, the gas/air being lighter than water, but will to some degree self bleed when the pressure builds up too much.

The temp sensor readings jumping around are *probably* due to the sensor probe going from being in coolant to not.

The one thing that would concern me regarding it being a head/head gasket, would be the lack of pressure at the radiator cap.

But the rest sounds like at least a head gasket.
What year is the car? EU2 or EU3?

If it's older it could still have the plastic dowels, the head will shuffle and wreck the head gasket.
I've even seen the plastic dowels being used again (new ones)when the head gasket has been changed, and it will then last another 100 000 km and let go again.

Use the steel even in the early heads although I think the land Rover official docs say you can't in the early ones.

The head will need to be tested for hardness if it is to be reused, as well as cracking/warping.

Cheers
James

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The vehicle is 2005 td5 defender. Not sure if the previous owner has had the head off. It has done 180000kms

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Originally Posted by Franksd

The vehicle is 2005 td5 defender. Not sure if the previous owner has had the head off. It has done 180000kms

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I'd get the coolant checked for exhaust gas, then you know for sure, are any hoses leaking?

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Originally Posted by shack

I'd get the coolant checked for exhaust gas, then you know for sure, are any hoses leaking?

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The only leak I have is a small weep from the top bees screw which occurs when the hose goes hard. My mechanic suggested the crack may be so small and only opening up under specific conditions so testing the coolant probably won’t tell me anything.

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Originally Posted by Franksd

The only leak I have is a small weep from the top bees screw which occurs when the hose goes hard. My mechanic suggested the crack may be so small and only opening up under specific conditions so testing the coolant probably won’t tell me anything.

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Doubtful, once the gases from engine combustion have made their way into the coolant they will remain there.

Secondly it's almost impossible to tell whether it's just a head gasket without pulling the head off, unless you've had it proper hot... 120°^ if you have had it this hot then yes you will also require a replacement head.

I’d put money on a head gasket
Just do the radiator and oil cooler at the same time
Don’t forget injector washers and seals

Use steel dowels and go again

Another thing to suspect would be the temp sender itself.
They aren't infallible.
Also the connector and or wire to it.
Check for a secure connection of the wire at the sender unit, give it a spray(WD or whatever you have).
If you could test the temp sender yourself would be cheap and easy way to be sure you're not getting false readings.
Otherwise just replace the sender unit.
Do you have a infra red thermometer to play with. If so, use it on the head to double check actual temps. In not, even the cheapies off ebay work well enough for diagnosing issues.

Going by the description that the coolant reading jumped from 83 to 89 and then back in a matter of seconds, I'd say it's a cable/connector issue.
I've had this myself on my 300 Tdi. I have a VDO style temp sensor on the top coolant bleed port leading to a thirdparty gauge. The location of the sensor rubs on the bonnet felt stuff, just lightly enough that with vibration the cables connector used to come loose off the sensor. The thirdparty temp gauge(digital readout) would show fluctuation in temp in seconds ... ie. no head gasket issue!

Also .. get an IR temp probe! [thumbsupbig]

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Originally Posted by AK83

Another thing to suspect would be the temp sender itself.
They aren't infallible.
Also the connector and or wire to it.
Check for a secure connection of the wire at the sender unit, give it a spray(WD or whatever you have).
If you could test the temp sender yourself would be cheap and easy way to be sure you're not getting false readings.
Otherwise just replace the sender unit.
Do you have a infra red thermometer to play with. If so, use it on the head to double check actual temps. In not, even the cheapies off ebay work well enough for diagnosing issues.

Going by the description that the coolant reading jumped from 83 to 89 and then back in a matter of seconds, I'd say it's a cable/connector issue.
I've had this myself on my 300 Tdi. I have a VDO style temp sensor on the top coolant bleed port leading to a thirdparty gauge. The location of the sensor rubs on the bonnet felt stuff, just lightly enough that with vibration the cables connector used to come loose off the sensor. The thirdparty temp gauge(digital readout) would show fluctuation in temp in seconds ... ie. no head gasket issue!

Also .. get an IR temp probe! [thumbsupbig]

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Thanks for the advice. I have a thermal camera so might use that to confirm if the sender is playing games. I will definitely be investigating further.