Hi guys, My 66 Reg 2.0l SE Technology recently developed a low oil/low coolant/oil in the coolant problem. No error messages or high temperature noticed until “check coolant” message appeared on starting one day. Black oil sludge mixed with coolant in expansion tank which was a bit low (tank so opaque can’t see through to judge easily). Also oil was almost down to minimum mark on dip stick.

Took to local garage who confirmed oil in expansion tank, explained about bag in expansion tank, mentioned likely oil cooler problem, but couldn’t help anytime soon due to long list of other jobs and staff taking holidays. Suggested local VAG specialist.

Local VAG specialist said the most likely problem and cheapest solution (£400) was an oil cooler failure, with the oil (presumably under greater pressure than the coolant) getting through some crack into the coolant. The solution being a new oil cooler, flush out coolant system and replace with new coolant etc. followed by a recommended second flush after about 500 miles.

The other possibilities mentioned were cylinder head gasket, and third was cylinder head itself - both were suggested to be probably terminal due to cost of inspection and repair vs residual value of car (180,000 miles). As an aside he also mentioned that once cylinder head taken off and seal broken, new job was never as good as old engine.

So had oil cooler replaced (and expansion tank). Since then I have done two 200 mile trips checking regularly en route. First trip showed a slight loss of coolant but no noticeable oil loss. Some black sludge still apparent in coolant when I dipped a wooden splint into expansion tank, but while noticeable was much more like new coolant. So took into the VAG specialist and was topped up and I was told could have been due to an air lock clearing in coolant system.

However, after second trip it showed a slight oil loss (2mm on dipstick) but an almost totally empty coolant expansion tank. N.B. No check coolant message.

This seems to be a fundamentally different set of symptoms compared to the initial problem where oil loss was much greater and coolant level loss much less (presumably due to oil in coolant forcing coolant out). Also no warning messages at all for coolant or oil.

Any hope? Any suggestions?

Thanks in advance.

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

However, after second trip it showed a slight oil loss (2mm on dipstick)

Could just be burned. 2mm isn't much at all and almost within margin of error considering how and when it is checked (eg hot or cold, some oil still not drained back to sump after running engine for a bit)

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

but an almost totally empty coolant expansion tank.

Possibly same as this

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

been due to an air lock clearing in coolant system.

Maybe they didn't bleed it properly.

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

Some black sludge still apparent in coolant

May require a coolant flush as the VAG garage suggested. Some residual oil in coolant system is expected.

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

Also no warning messages at all for coolant or oil.

2mm of oil loss not gonna show a warning.

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

So had oil cooler replaced

I'd say this was the cause and you are seeing some effects of residual oil and an unpleasant system.

I'd keep topping it up and watch it. If still using coolant after 500 miles, maybe another leak.

I'd certainly be letting the garage know as their inability to bleed the system properly may cause damage to the cylinder head.

On 15/09/2025 at 19:21, DefinitelyDodgyDave said:

So took into the VAG specialist and was topped up and I was told could have been due to an air lock clearing in coolant system.

This is where they admitted it may not be properly bled. I think it will be fine but a significant air lock can cause overheating in parts of the head which will lead to cracking.

Run the heater a bit to promote coolant flow. That might help bleed the system

Edited 24 September, 202524 Sep by BlueWagon