Coolant under Rocker Cover

The specimen: 2000 Defender 110 Td5 LHD (245,000 km)

Purchased with 226,000 km on the clock approx 1 year ago. It's had a coolant leak from day one however the leaks were visible around top hose, thermostat, radiator and would puddle under car when parked. The coolant was flushed a few weeks after purchase. Since then, new radiator, thermostat, top hose and expansion cap installed - still losing coolant.

Things gradually got worse to the point of heavy white smoke on start up and while driving engine would stutter at 100km/h . Head gasket replaced last October, white smoke eventually cleared and the exhaust is now normal. Coolant is still disappearing at the rate of 1l per 5-600 km of driving. Other parts replaced since October: valve cover gasket, fan clutch assembly, MAF sensor, exhaust manifold gasket, turbo gaskets, oil pressure sender, intercooler, vacuum pump feed hose.

The coolant system has been pressure tested numerous times and holds pressure. While removing the rocker cover to replace the injector wiring loom (red ECU plug was contaminated with oil), I noticed traces of coolant under the cover:



Cleaned and checked 1 month later, same traces of coolant. The car runs well, no visible signs of coolant leaking in the engine bay, the three core plugs are dry.

Local LR mechanic is stumped - any ideas?

A guess but the head could be lifting causing coolant to mix with oil. Is it tuned at all? Being a pre 10p engine they have plastic locating dowels which can fail

bankz5152 said:

A guess but the head could be lifting causing coolant to mix with oil. Is it tuned at all? Being a pre 10p engine they have plastic locating dowels which can fail

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It's not tuned, plastic dowels were replaced with steel when HG was done.

Where new studs used?

You have pressurised coolant leaking into low pressure oil, have you checked the sump for coolant? If it's just in the cam cover check for leaking coolant gallery plugs.

bankz5152 said:

Where new studs used?

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Not sure but I suspect they would have been replaced if needed. I also neglected to mention that the block was skimmed when the HG was done.

wammers said:

You have pressurised coolant leaking into low pressure oil, have you checked the sump for coolant? If it's just in the cam cover check for leaking coolant gallery plugs.

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I've only checked oil from the filler cap, are you recommending to drain it completely from the sump plug? If the gallery plugs are the same as core plugs they are dry.

Tommieboy said:

I've only checked oil from the filler cap, are you recommending to drain it completely from the sump plug? If the gallery plugs are the same as core plugs they are dry.

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No the dip stick should show up coolant in oil, if there is enough of it oil will be milky. Are you sure it is coolant in the cam cover and not just moisture caused by short runs and bad engine breathing. You maybe losing coolant elsewhere and have just not found the leak.

wammers said:

No the dip stick should show up coolant in oil, if there is enough of it oil will be milky. Are you sure it is coolant in the cam cover and not just moisture caused by short runs and bad engine breathing. You maybe losing coolant elsewhere and have just not found the leak.

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Oil on dipstick looks good and maintains proper level, no milky appearance. The color of what I found under the rocker cover is green and closely resembles my ethyl glycol conventional coolant - I could be mistaken but I'm quite sure it's coolant. My runs are a mix of 15 - 60 km daily. Oil/filter and air filter are changed regularly.

Have you double checked under the vehicle for the lost coolant?

A good hiding place for a slow leak on the Td5 is under the turbo, at the back of the oil cooler.

Cheers

neilly said:

Have you double checked under the vehicle for the lost coolant?

A good hiding place for a slow leak on the Td5 is under the turbo, at the back of the oil cooler.

Cheers

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Thanks, I will check in case there's a slow dribble that dries off while driving but the ground when it's parked is dry...of coolant.

Tommieboy said:

Thanks, I will check in case there's a slow dribble that dries off while driving but the ground when it's parked is dry...of coolant.

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While you are there also check the plug behind the exhaust manifold. They are known to leak.

Cheers

If there was a litre of coolant leaking into the engine oil every 300 miles the oil would be like milk.

wammers said:

If there was a litre of coolant leaking into the engine oil every 300 miles the oil would be like milk.

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It may well be something else, these are the observations I've made so far. I can't say definitively that the entire coolant loss is going into the oil just that I've found traces under the rocker cover as per the pic above. I'll check more closely behind the exhaust manifold and under the turbo as was suggested.

neilly said:

While you are there also check the plug behind the exhaust manifold. They are known to leak.

Cheers

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I had that bar steward thing!

checked plug behind exhaust manifold took off heat shield and checked behind turbo and oil cooler - all dry. Checked the oil dipstick again, proper color, proper level.

What's also strange is that the coolant level in the expansion tank fluctuates considerably. The last few rides I've checked it immediately after arriving home. I slowly release the cap and let off the pressure, yesterday it was down almost 1.5" from the cold fill line and after checking today it was only down by 1/4". I didn't top it up yesterday, in fact I haven't topped it for the last 200 miles or so. I'll keep an eye on it and see how far I get without topping up to the point of needing a top up. Is it better to check the level the next morning after it's completely cold or does slowly releasing the cap achieve the same result?