Time for a new head?

Evening all,
My coolant loss continues.... on a long hard pull coolant will start spewing out through the cap. I’ve mentioned this before but it was suggested it was down to coolant flow, I’m not entirely convinced as I’m sure it would also do it at idle?
Anyway I’m thinking cracked head... could this be possible? 10P td5 Defender 97k miles

Tom could this not just be a head gasket that is required? It would be a damn sight cheaper than a new head

Discodevon said:

Tom could this not just be a head gasket that is required? It would be a damn sight cheaper than a new head

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With no other symptoms? I’m going to do a pressure test on the coolant system later in the week

tom1979 said:

With no other symptoms? I’m going to do a pressure test on the coolant system later in the week

Click to expand...

Yes it would seem you’re coolant is pressurising which would indicate head gasket failure, but then I may be wrong? Is changing the head gasket a job you could do?

Discodevon said:

Yes it would seem you’re coolant is pressurising which would indicate head gasket failure, but then I may be wrong? Is changing the head gasket a job you could do?

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Think I could manage that!

Several people tonight have suggested
Cracked head since it only occurs under heavy load when driving. Im not going to rush out and buy an amc head but I wanted to know if this could be a possibility

tom1979 said:

Think I could manage that!

Several people tonight have suggested
Cracked head since it only occurs under heavy load when driving. Im not going to rush out and buy an amc head but I wanted to know if this could be a possibility

Click to expand...

If the head was cracked wouldn’t you have water in the engine oil or the other way round?

Discodevon said:

If the head was cracked wouldn’t you have water in the engine oil or the other way round?

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Personally I would expect all kinds of **** to be going on but I suppose it depends where the crack is (or where the gasket is damaged)

IMO with a crack which brings combustion gas into the coolant to pressurise it the engine should overheat under load cos the coolant is mixed with 400*C hot gas ... and then the coolant should leave through the overflow pipe not through the cap... better try with another new cap and make sure it seals well

sierrafery said:

IMO with a crack which brings combustion gas into the coolant to pressurise it the engine should overheat under load cos the coolant is mixed with 400*C hot gas ... and then the coolant should leave through the overflow pipe not through the cap... better try with another new cap and make sure it seals well

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I think 6 brand new genuine caps is enough! I'm not getting any overheating, which is puzzling. There's no overflow pipe on a Defender?

Have you changed thermostat and it's been fitted wrong the dog leg should be facing engine block
Just a thought I've seen it done and it causes all sorts of issues

triggersbroom said:

Have you changed thermostat and it's been fitted wrong the dog leg should be facing engine block
Just a thought I've seen it done and it causes all sorts of issues

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I haven't changed it yet, I have never changed it in the 7 years I've had the vehicle. I am going to do a pressure test on the coolant system tomorrow when the proper kit comes (normally use some garden hose and a Schrader valve!). I would upload a data log of it happening but there seems no way of doing it here. @sierrafery makes an interesting point about the overheating. When it happens the max temp is 94*C which I would expect anyway during that kind of driving. During my test run last night the max temp on the whole 5-6 mile trip was 100*C.

Just thought, I could Dropbox it : https://www.dropbox.com/s/8rszhy5sllupyd2/NEW-17092019.CSV?dl=0

Things I am wondering about:

- I changed for an Allisport (please don't laugh, and no I didn't have to wait 6 months for them to make it ) header tank just before Christmas and then this started. I then changed for a new plastic header tank although not genuine one (Allmakes PCF101530). I changed from the allisport one back to plastic because I thought maybe the threads weren't right.

- I have never changed the thermostat (although no reason to)

tom1979 said:

I think 6 brand new genuine caps is enough!

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yes that's enough... try with the third tank then

sierrafery said:

yes that's enough... try with the third tank then

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What sort of temps would I expect if the coolant was being pressurised from combustion gas ?

All the cases i've seen with combustion gas leak into the coolant were overheating... which means the gauge went to the red zone(120*C +) and the top hose rock solid... which is logical, what ever problem occurs the coolant MUST leave the system through the overflow pipe, it is not supposed to be any way for the coolant to pass near two o-rings and a seal while there is a release valve built into the cap to let the coolant to the overflow

sierrafery said:

All the cases i've seen with combustion gas leak into the coolant were overheating... which means the gauge went to the red zone(120*C +) and the top hose rock solid... which is logical, what ever problem occurs the coolant MUST leave the system through the overflow pipe, it is not supposed to be any way for the coolant to pass near two o-rings and a seal while there is a release valve built into the cap to let the coolant to the overflow

Click to expand...

And with there being no overflow on the Defenders I’m guessing it has to go through the cap?

BTW ... did you try all those 6 caps on the allisport tank then fitted the plastic back and tried on it? ...cos if the metal tank has a problem it could have ruined all those caps, i insist that there should be no way for the coolant to get out near the cap and not through the overflow in case of overpressure

EDIT... i misssed that it's about a defender, sorry

sierrafery said:

BTW ... did you try all those 6 caps on the allisport tank then fitted the plastic back and tried on it? ...cos if the metal tank has a problem it could have ruined all those caps, i insist that there should be no way for the coolant to get out near the cap and not through the overflow in case of overpressure

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noooooo! New caps with new tanks.

There’s no overflow on defenders, it has to come through the cap vent????

I copied this from the Defender Td5 workshop manual

Publication Part No. LRL 0410ENG (2nd Edition)
Defender Td5
Land Rover 2001

26 COOLING SYSTEM



The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to

allow excessive pressure and coolant to vent through the overflow pipe. The relief valve is open at a pressure of

1.4 bar (20 lbf.in) and above.

I have not much experience with defenders

sierrafery said:

I copied this from the Defender Td5 workshop manual

Publication Part No. LRL 0410ENG (2nd Edition)
Defender Td5
Land Rover 2001

26 COOLING SYSTEM



The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to

allow excessive pressure and coolant to vent through the overflow pipe. The relief valve is open at a pressure of

1.4 bar (20 lbf.in) and above.

I have not much experience with defenders

Click to expand...

I’m not sure what they mean then as there are two outlets on the tank, one at the bottom and a small one on the side which is the return.

They might have copy/pasted the description from the D2 manual then cos even the component layout diagram looks similar with the square tank while the defender has a round tank... i'm a bit stumped about this kind of setup but i can see now that in case of overpressure the coolant can get out only near the cap on a defender