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[kingers]

The car has been lying up for 2 months and I've been doing a few jobs as I'm putting it back on the road.

My old header tank used to weep a bit of coolant through the cap, I'd say about a cupfull every 500 miles, the coolant level sensor was also shot in it so I replaced the tank with a 2nd hand one with a good sensor.

I filled it back up with roughly 50/50 coolant mix.  Now it has started drinking coolant - about 1.5 litres in 150 miles (90mph motorway drive).....

I went out to it today and filled it up from cold to the correct level, left cap off and ran the car until warm to ensure there was no air in the system.

I then gave it a good reddining (cap on) and examined the pipes for leaks - nothing.

No mayonnaise on filler cap or dipstick, no white smoke when it's hot, so is that enough to rule out Head Gasket Failure?

Any thoughts on what this is / how to diagnose the problem?

[freecall666]

put some water dye in even food colour will work but not in exhaust systerm(will not see it), run till up to pressure and leave it, come back when cooled down and have a good look round top pipe is a good place to look top pipe on front rad, or radiator cell is another.

[henryd]

Any sign of leakage under the car ?

[cem_devecioglu]

The car has been lying up for 2 months and I've been doing a few jobs as I'm putting it back on the road.

My old header tank used to weep a bit of coolant through the cap, I'd say about a cupfull every 500 miles, the coolant level sensor was also shot in it so I replaced the tank with a 2nd hand one with a good sensor.

I filled it back up with roughly 50/50 coolant mix.  Now it has started drinking coolant - about 1.5 litres in 150 miles (90mph motorway drive).....

I went out to it today and filled it up from cold to the correct level, left cap off and ran the car until warm to ensure there was no air in the system.

I then gave it a good reddining (cap on) and examined the pipes for leaks - nothing.

No mayonnaise on filler cap or dipstick, no white smoke when it's hot, so is that enough to rule out Head Gasket Failure?

Any thoughts on what this is / how to diagnose the problem?

I'm afraid no.. gaskets develop a small leak point at the beginning (which mine did) and give none of the obvious hints..

[ScaniaV8]

Have you checked out the normal culprit...the dreaded HBV. ??

I also dumped lots of coolant via this horrible little device stuck in a shitty location at the back of the engine underneath scuttle and wiper motor.

Pressure test system would I'm sure give you the source of the leakage, advice in the maintemance guides is useful as is one for HBV replacement.

good luck.

[kingers]

Thanks guys, I think I've found it, signs of sprayed coolant at filler cap and top of airbox so the cap needs replacing I think. Fingers crossed!

[Andy B]

Thanks guys, I think I've found it, signs of sprayed coolant at filler cap and top of airbox so the cap needs replacing I think. Fingers crossed!

check the neck of the header tank, it's not unheard of for them to crack here. A new header tank is IRO £35