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[RolandL]

I have been chasing a coolant loss problem for some time. Current rate of loss is from correct level to coolant low light, one week.

 I have changed the HBV, Radiator and the water pump (which was showing some signs of the seal leaking) slight improvement, but still losing coolant.

  I have also changed the thermostat, O ring (also showing signs of seal leaking) and transfer pipe O rings  no improvement in loss.  I have checked all the coolant hoses and unions, no signs of any leaks.  There are no signs of any leaking fluid on the ground or around the engine.   Have also checked the expansion tank, no signs of any leaking. No oil residue in the expansion tank and no signs of water (emulsion) in the oil, other than some on underside of cap.  But this is no more than usual as wife does short journeys, and not present on longer runs.

Also checked inside cabin, all dry no signs of water leaking from the heater matrix.

I am at a loss as to what to do next.  Any ideas??

Roland


Also have a slight knocking noise from under a cam cover, which sounds like a sticking hydraulic lifter.  Is Forte Top end treatment any good for unsticking it?

[JamesV6CDX]

Coolant bridge, oil cooler plate, nearside head gasket, all possibilities

What's the year, engine, mileage and coolant history?

[JamesV6CDX]

Would be worth pressurising the cooling system with the valley exposed and engine cold to help ascertain where it's going

[RolandL]

Hi James,

It's a '99 Mini Facelift 2.5.  190k

Coolant changed every 2 years.

If it was the oil cooler plate or the head gasket (why nearside?) wouldn' it show in the oil and expansion tank? Forgive my ignorance but where is the Coolant bridge?

[amba]

Had a similar mysterious coolant leak for several years with my old 2.5..1998...eventually went for sale at 228k

Did everything you have done and eventually concluded that it was the n/s head gasket at the back edge.It seems that the gasket in effect rots due to years of leakage from the scuttle area which destroys just the water seal on the gasket.Given the age/mileage of mine and it only being a small loss which never got worse as in effect the head area is quite high up,I just put up with it and checked coolant/topped up more regularly than most.

Coolant bridge is at the back of the valley behind the oil cooler plate and has dowty washers that seal the hollow bolts into the block.Washers have been known to fail as also the 0 ring on the transfer pipe which sits below that so all possible areas.   

[TheBoy]

head gasket (why nearside?) wouldn' it show in the oil and expansion tank?

1998 3.0l appear to have a weakness at rear of cyl6. Not seen it on a 2.5 though, so hopefully your safe

Coolant leaks to outside, and drips off bellhousing

[vauxsull]

More than likely its my nearside head gasket gone on my X plate 2.5... Everything else has been changed or resealed.. Only got 115k on the clock too

[dbug]

Coolant bridge, oil cooler plate, nearside head gasket, all possibilities

What's the year, engine, mileage and coolant history?

I would look at these, plus radiator, if other avenues exhausted.

Re your knocking lifter - does it go away with running?  Regular/frequent oil/filter changes often cure, I've used the Wynn's lifter treatment product in the past which has helped.

[JamesV6CDX]

head gasket (why nearside?) wouldn' it show in the oil and expansion tank?

1998 3.0l appear to have a weakness at rear of cyl6. Not seen it on a 2.5 though, so hopefully your safe

Coolant leaks to outside, and drips off bellhousing

Although as a forum we first started seeing this on 1998 3 litres, I'm afraid I've also seen the exact same failure on 2.5's of that Era

I think the most recent 2.5 to suffer this was Sir Tiggers

With the mileage, if it's not the cooler plate or bridge, it does to me still seem likely

[JamesV6CDX]

Should also say I've seen it on a couple of 2000 mv6's, my V plate the most recent

Never seen it on a 2.6 or 3.2 with multi later metal gaskets

[Nick W]

Both gaskets on my 2000 3.0l were rotten at the back. It ran OK, but was losing water as steam; I could see it from the exhaust. Surprisingly, it wasn't pressurising the cooling system.

[JamesV6CDX]

Both gaskets on my 2000 3.0l were rotten at the back. It ran OK, but was losing water as steam; I could see it from the exhaust. Surprisingly, it wasn't pressurising the cooling system.

This is because the mode of failure is between the water jacket and the outside world, the fire rings around the pistons are the one thing that remains intact

Which is why testing for the presence of exhaust gasses in the header tank in this situation won't tell us anything

[TheBoy]

Both gaskets on my 2000 3.0l were rotten at the back. It ran OK, but was losing water as steam; I could see it from the exhaust. Surprisingly, it wasn't pressurising the cooling system.

This is because the mode of failure is between the water jacket and the outside world, the fire rings around the pistons are the one thing that remains intact

Which is why testing for the presence of exhaust gasses in the header tank in this situation won't tell us anything

Which shows Nick W's was a different failure mode, if it was coming out of the exhaust

[Nick W]

That was my point; I could understand it leaking out of the head joint and down the block, or the combustion pressurising the cooling system but not the coolant leaking into the cylinder.

[YZ250]

head gasket (why nearside?) wouldn' it show in the oil and expansion tank?

1998 3.0l appear to have a weakness at rear of cyl6. Not seen it on a 2.5 though, so hopefully your safe

Coolant leaks to outside, and drips off bellhousing

I have, on my old 2.5 at around 80K. Nearside rear outer corner, the engine heat dried it before it became visible so the leak was a pain to find. Only exterior sign was a whitish salty mark on the block in that area. I was unaware of the 1998 issue at that time.