Another coolant leak!

Johnr32 · Post by **Johnr32** » Sat May 12, 2018 12:32 pm

Ok so the z4 is driving me mad. I've replaced the expansion tank, thermostat and the temp coolant sensor now.

It only seems to drip coolant when I open the cap on the expansion tank to check the level. Seems to drip just below the expansion tank area. The dripping stops after an hour and there is no leaking under a compression test (1bar) or when the engine is hot and running.

Any ideas as I'm ready to drive it off a cliff.

firebobby · Post by **firebobby** » Sat May 12, 2018 12:41 pm

If it's not loosing water when left alone... then it leave alone and see after a week or so if the coolant level has dropped. If not, it must be something to do with an over flow on the cap maybe.

Scooba_Steve · Post by **Scooba_Steve** » Sat May 12, 2018 1:03 pm

Tried a new cap?

Johnr32 · Post by **Johnr32** » Sat May 12, 2018 2:15 pm

It doesnt leak when the car is hot and during/after a very spirited drive then I doubt its the cap? It seems to only leak (tiny drips) when its cold and only when I open the expansion cap (doesnt physically make any sense what so ever?) Will try and get under the car after work and when its not raining to get a better visual.

Scooba_Steve · Post by **Scooba_Steve** » Sat May 12, 2018 2:30 pm

Usually I'd expect the cap to leak under pressure but if you're right that it only leaks when you take off to check then surely a new cap is worth a try.

Scooba_Steve · Post by **Scooba_Steve** » Sat May 12, 2018 2:30 pm

And also a cheap attempt!

firebobby · Post by **firebobby** » Sat May 12, 2018 5:34 pm

Johnr32 wrote: ↑Sat May 12, 2018 2:15 pm It doesnt leak when the car is hot and during/after a very spirited drive then I doubt its the cap? It seems to only leak (tiny drips) when its cold and only when I open the expansion cap (doesnt physically make any sense what so ever?) Will try and get under the car after work and when its not raining to get a better visual.

So if you don't take the cap off, it doesn't leak when hot or cold ? If this is the case, leave the cap alone.

Johnr32 · Post by **Johnr32** » Sat May 12, 2018 6:26 pm

firebobby wrote: ↑Sat May 12, 2018 5:34 pm
Johnr32 wrote: ↑Sat May 12, 2018 2:15 pm It doesnt leak when the car is hot and during/after a very spirited drive then I doubt its the cap? It seems to only leak (tiny drips) when its cold and only when I open the expansion cap (doesnt physically make any sense what so ever?) Will try and get under the car after work and when its not raining to get a better visual.
So if you don't take the cap off, it doesn't leak when hot or cold ? If this is the case, leave the cap alone.

Leaving the cap alone isnt my style as I like to check all fluids weekly. I'll have a proper look when its not so wet outside.

Rufus59 · Post by **Rufus59** » Sat May 12, 2018 8:45 pm

Stupid question, are you sure it's coolant? I ask because I mistook water on the under tray for coolant until i dabbed it with a tissue and noticed it had no colour.

jack07 · Post by **jack07** » Sat May 12, 2018 9:57 pm

Try the cap change,and clean the plastic threads,then a little silicone spray on them before tightening

Johnr32 · Post by **Johnr32** » Sun May 13, 2018 11:21 am

http://s84.photobucket.com/user/johnthe ... sort=3&o=0

Seems to be dripping from the bottom of the expansion tank then down to the lower radiator hose and blue drain plug? is there an o-ring at the bottom if the expansion tank? could it be a faulty expansion tank even though its new?

Grumpyowl · Post by **Grumpyowl** » Sun May 13, 2018 3:23 pm

I have a similar problem. Replaced expansion tank, both drain plugs, bleed plug coolant temperature sensor and water pump.
Went out for roughly a 50 mile run yesterday everything perfect the car is driving superbly.
Checked the coolant level this morning and it's lost about half a mug full of fluid. Looking below the expansion tank and I can see a slight drip the top 2 hoses are completely dry can only think it maybe the bottom hose !!!

It'll have to wait till next weekend now to get it on ramps and again remove the engine cover all very frustrating .

Johnr32 · Post by **Johnr32** » Sun May 13, 2018 4:34 pm

Grumpyowl does yours leak when hot and running? Mine seems to only do it when it's cold even then it's not all the time.

Grumpyowl · Post by **Grumpyowl** » Sun May 13, 2018 6:09 pm

John I'm confused to be honest, I think the problem is when it's hot and things have expanded.
However the car runs perfectly and the temperature gauge never goes above normal .
After topping up when cold it does seem to hold its level maybe the float drops a tiny fraction .

The car has been layed up over winter, I first noticed a problem after letting it idle to temperature then running an engine flush for 20 mins before an oil change. After putting it back in the garage, the next day I noticed a fluid spill on the garage floor.

After a good run of 70 miles over to DLV for Vanos seal upgrade when I got there the fluid level was low.
Mike did a preasure test and there was no leakage.

Driving the car home everything was ok but after checking the next day the fluid was down.

Hence like you doing a maintenance upgrade with expansion tank, temp sensor, water pump and drain plugs.
There was no sign of problems with any of the hoses .
I thought I'd cured it until we went out for a run round derbyshire yesterday about 50 miles the car ran perfectly.

Checking the coolant this am and I'd lost about half a mug full and there seems to be a small drip under the expansion tank, the top 2 hoses seem to be dry and now I'll have to get it up on ramps and check the bottom hose but I'm only guessing at the moment.

Grumpyowl · Post by **Grumpyowl** » Mon May 28, 2018 10:00 am

@ Johnr32, Did you get this sorted ?
Cured mine put new radiator (expansion tank) Cap on, the preasure from this blew the bottom hose.
Which was good news as that confirmed my suspicions . new hose fitted, been driving and checking it all weekend and touch wood all seems to be fine now.

Hope you sorted yours

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