D4 2.7 mystery coolant leak

[Squanderer]

This much-loved and proactively maintained second owner vehicle has a mystery leak that is getting worse but is inconsistent. Initially noticed leak apparently from coolant bottle cap after driving a long day back from Canowindra to Blue Mts, as if over-pressuring . Took to mechanic( trusted well known Sydney indie who I respect) who pressure tested and couldn't find anything so we agreed to replace the EGR pipes as it may have been leaking down the exhaust. Pipes subsequently bypassed as coolant loss continued after drive sydney to canowindra again (300ml loss) and again coming back from trip to Singleton to sydney (700ml loss in total there and back), which I detected when the low coolant light came on the next morning when I went to start it from cold (and then topped up the estimated 700mls ).

Following the latest repair, just had another trip to from sydney to Turon over Blue Mts-lost nearly a litre. Return trip, barely lost 50ml. Bizarre. Mechanic suspects head gasket but no bubbling in coolant bottle when cold, no coolant in oil or vice versa, no low coolant light (except on cold start-up after Singleton trip), performance not affected. Just once, engine (?? or under bonnet noise) made odd noise like chuffing briefly for 5 seconds or so on a hill this most recent trip, but not otherwise on any other inclines. (and we have done a few).

Engine has done about 160000km and car 300000km. Radiator new, coolant bottle (and I assume lid) new, EGR bypassed including pipes, pressure tested, no visible leaks and I asked for the front inlet plastic housing on top of the v of the engine to be replaced as well after the first time the leak was detected.

My googling suggests possible culprits are the water pump, a plastic inlet on the left side of the block (??), coolant bottle cap and possibly a dud replacement inlet on top of the v of the engine? But i can't for the life of me see any drops except a couple down near the coolant bottle. Smell of coolant noticeable. I want to discuss with the mechanic and see if we can do what we can before I contemplate the body off and $$ of head gaskets? I have already spent a great deal with the EGR aspect. (I assume body off for gaskets??). Forum search suggests Hg is uncommon, unless from a catastrophic failure with massive coolant loss.
Any thoughts?

Thanks
Squanderer

[Eric SDV6SE]

Oil cooler sitting in the V leaking coolant into the void between the two banks, this then either evaporates or drains down the back of the block externally when driving.

Plastic fitting into the block can crumble if disturbed, but then you'd lose all the coolant at once.

Head gasket - unlikely if engine is still running well, being a diesel they run high compression so a head gasket leak is pretty evident.

[Squanderer]

Thanks Eric I’ll add oil cooler to the checklist.

[Tombie]

Is the coolant bottle OEM / Genuine? What about the Cap?

If eaither of these arent, throw them out!

[CountOtto]

I recently replaced my coolant bottle and noticed a small leak on the bleed valve on the bottle . Turns out the O ring wasn’t sealing when hot leaking coolant. Replaced with larger O ring and all good. The only telltale sign was a very small trace of red coolant down the side of the bottle.

[Squanderer]

Is the coolant bottle OEM / Genuine? What about the Cap?

If eaither of these arent, throw them out!

Both genuine thanks Tombie and replaced recently (8 months ago). Having the car pressure tested again over the whole long weekend, will try new cap anyway and larger o-ring as per next post and renew water pump otherwise it's massive dollars. I'm meant to be driving out to the Dig Tree and back from Sydney in July with mates and won't do it with a leak

[RANDLOVER]

I had a similar leak, that would need topping up randomly and not show on pressure test, turned out to be the plastic dog leg fitting into the lower part of the block, which broke off when my mechanic tried to remove the hose, unfortunately the leak corroded one of the securing bolts so took ages to remove.

[Squanderer]

So, indie ran out of time to do head gasket on my D4 2.7, which was the only thing we arrived at as the cause (sometimes losing coolant, no source, only occurs when under load eg going up over the Blue Mts from Sydney, but, weirdly, not coming back. Nil other HG symptoms eg no coolant in the oil, no oil or diesel in the coolant, nil loss of power, nil white smoke on startup (only blue puffs, ho ho)). The system was pressurising, no obvious coolant leak, possible culprits changed eg top of engine valley plastic bit, and including, most recently, water pump. Elbow checked (see previous post). Drove home last night all of 35 mins, going up a small but steep hill, smelt coolant. Checked under bonnet at home 2ks later. Small leak from reservoir cap.

So here's the thing: my supposedly genuine cap says 'FOMOCO', made in India. I assume it's one for a Territory 2.7. I just had a new cap arrive in the post, also supposedly genuine LR one, with green and white packaging sticker saying 'Bearmach, Land Rover, made in Canada'.. It looks better printed (red warning sticker etc, some sort of plastic black fitting/ventilated shroud over the relief valve spring thing at the inside top of the cap (where the FOMOC one had no protective shroud), dark grey rubber seal rather than black, which to me looks like a flat-faced washerBearmach cap.pdfFOMO cap.pdf rather than an o ring, but I have no mechanical knowledge/training so I'm not sure). I will try that. Can anyone comment on whether the FOMOCO one is also genuine or not?

Also took cap off and watched coolant for bubbles. Couldn't smell anything like exhaust but will have to get hydrocarbon(?) test done. There were bubbles, but it was like the froth of a garden hose, coming from the thin black rubber pipe that comes across the radiator from the driver's side and enters the reservoir near the bleed screw, pumping coolant in. The coolant in the main part of the reservoir wasn't moving. From another Aulro thread this bubbling from coolant being pumped in is apparently normal?

Anyway, off to get hydrocarbon testing done and maybe try another hill with the new cap on...and then fingers crossed on an outback camping trip that people will travel into Sydney from OS and interstate for, and which I can't cancel, after a year's planning.

[Squanderer]

PS just noticed the o ring sitting on top of the seal. D'oh!

[Squanderer]

PPS just noticed the FOMO one doesn't have an o ring! I will call myself stupid before anyone else does, but feel free. What I thought was the o ring was just the rubber washer. So hopefully I have just saved myself thousands...Now back to the D2 with the leaking water pump and Ace pipe