loosing coolant

[jumbojake]

bit puzzled by this.

on my last service, I noticed my 2013 IS200d had low coolant level.  I topped up and it dropped again... I keep adding, but it drops, pretty quick (below 'low' line)..and stops... even after another 500mile round trip, it doesn't appear to drop much further.  I topped up again tonight, and after 5miles it was again below the low line

If there was a leak, having dropped so quick.... a long drive would have emptied it.

If the pressure cap was weak, the overflow pipe would be wet (it isn't)

If the head was going, I'd have either have emulsified oil, or lots of smoke out the back .... don't have either.

I have not seem any movement in the temp gauge... rock solid in the same place it has been for  2years.

Any thoughts? 
 

[Fat Boy]

You need to get it pressure tested 

it could be leaking onto a hot spot 

these are the dangerous leaks that kills head gaskets 

if the level drops just below the head gasket line , the temp. Gauge will still read normal ,but burn the head gasket causing damage to many other parts 

get it sorted 

oil burner don’t like to be overheated 

[Britprius]

Most car cooling systems have two coolant top up points. One on the header tank with pressure cap, and another on the radiator without a pressure cap "just a sealing cap"

When the system is cold check the level at the rad cap. Fill this up right to the top of the filler point, and replace the cap. Then fill the header tank to the full level, and replace the cap. Check the header tank again after a run to see if this cures the problem.

John 

[johnatg]

That's not how the IS models are arranged.

There's no radiator cap as such - the pressure cap is located on the thermostat housing and is described as the 'Radiator pressure cap'.

The header tank has a non-pressure cap.

I suspect the OP has a head gasket problem. You don't necessarily get mayonnaise or other signs of oil leakage into the oil. The water can just go one way through a failing gasket - the failure point can act as a one way valve. Relatively small amounts of water don't show up in the exhaust - my MX-5 has water injection and nothing shows in the exhaust!

I agree with Terence - you need a pressure check - sooner rather than later.

[J Henderson]

Yup, a number of trucks at my place of work all suffered from cracked cylinder heads and didn't display any of the classic symptoms - mayonnaise oil, smoke etc. They just consumed more and more water until they finally packed-in.

[jumbojake]

I've had a good look and the expansion tank cap has a pressure relief valve integrated to it (not sure if this was a variant just for later IS200d).  I could see lots of coolant stains above the seal, so it has clearly been letting stuff out at some point.

I have fitted a new cap and so far seems stable..... something to keep an eye on... if it drops again it's time for a pressure test.