Coolant Problem ?

[BadgerUK]

Hello,

I have owned my 35 plate Z4 3.0 since June last year. In that time I have had to top the coolant up in the expansion tank a couple of times but only very very small amounts after I first picked it up. Since then it seemed ok and I stopped checking it regularly. A couple of weeks back I checked it again due to being under the bonnet and noticed it was almost completely empty. So I topped it up and have been checking it every weekend and once again its going down very slowly. I have googled this and seen loads of topics about coolant leaks but they always involve over heating problems or the coolant light showing on the dash, neither of which I've had.

Anyone have any idea what could be causing this before I give BMW a ring and ask them ?

Thanks

Stephen

 

[Stratts]

What's causing it? You have a leak in the system somewhere.

The cooling system is sealed/closed so any loss is down to a leak somewhere. Most commonly this is from one of the easily accessible spots at the front of the engine, so have a good look at the thermostat housing and all of hoses connected to the radiator. The tell tale sign is a small puddle of 'water' on the undertray.

The coolant system also runs into the cabin area to heat the car, the hoses for this are much smaller but you can easily see them (the benefit of the Z4 over other cars that share this engine) and they run alongside the intake manifold and near to the sound generator. Check all of the connections/hoses that you can physically see and reach to make sure they are completely dry.

Other things to check are the expansion tank itself (where it connects to the rad) and the water pump. For things like this it is always best to stick the car on ramps/stands and whip the undertray off and have a good root around with a torch from underneath. You will find it if you methodically the system.

As long as you can get heat from the cabin vents then you have enough coolant in the system (loss of heating is a telltale of imminent failure so be aware).

I deliberately haven't mentioned head gasket as a) it is highly unlikely and b) there are obvious symptoms of this and a very slow loss of coolant isn't typical (normally it's a bit quicker and you'll have steam from the exhaust).

Like I said, keep a close eye on it - as long as it remains a very slow leak and you are keeping an eye out for the signs of more urgent issues then you'll be fine. If the temp gauge ever moves even slightly above centre, stop immediately.

The chances are that one of the hoses (and especially the connections) has got a tiny leak. The light will only come on when your level goes below the switch at the bottom of the expansion tank, and as long as you keep checking it and topping it up you will not experience any issues, just don't let it drop too far or you'll let air into the system.

 

[BadgerUK]

Thanks for the reply.

Can you just expand on the head gasket part just so I can be 100% sure its not that. How quick is quick ? Talking a few hours of driving or days. Only "steam" I have seen from the exhaust is the normal stuff from a cold start at this time of year. Never seen any on a warm day or once the engine warmed up.

When we next get a decent weekend ill have another poke around the engine. Don't have the space (drives on a ramp) or tools to do much unfortunately.

 

[simonlpearce]

Hairline crack in expansion tank is most likely. Its a very common issue on the M54 engine.

Depending on mileage, if its anywhere near/above 80k, then i would start budgeting for a complete overhaul of the system. So Rad, Expension Tank, Thermostat (including housing) and water pump.

Also check the bottom of your rad to see if its bowed like a banana, another sign things are on their last legs.

 

[Stratts]

Hopefully others can join in as I've not had any experience of HG issues, but I'm talking obvious coolant steam (sweet smelling) from the exhaust, probably some rough running and eventual overheating, as well as oil in the cooling system and white mayo on the oil filler cap. Can't tell you the speed as it's dependent on how long you drive for. I would honestly discount it as an issue as it just complicates matters.

So, ignore HG and concentrate on the easier bits.

A decent torch and some kitchen roll will do a job, place the roll on the joints and hoses and other parts as mentioned and see if you can find any wet areas. It can be frustrating and time consuming (especially as sometimes any coolant loss will be hidden as it evaporates on a hot engine) and some leaks are only apparent when the engine is running, but you are losing it from somewhere.

Last resort (or maybe first) is to whip off the undertray and drive the car over a large piece of cardboard and see if you get any drips on it. You could leave it running or leave it overnight, it's a trick I've used in the past but it won't always find an issue (especially if the leak is from the heater matrix area).

 

[BadgerUK]

Thankfully my cars only just gone to 47k (30k when I picked it up), so hopefully its got a few more years in it before I start needing to change large amounts of stuff. And I have not got any of those issues associated with HG failure so hopefully that's ruled out.

Guess its a weekend inspecting hoses and parts and going from there. Depending on whether I decide to move to a Z4M sooner rather then later if I have no luck ill take it to BMW for a full test, oh well joys of cars.

 

[Bazoz4]

Signs of internal head gasket failure would be buildup of greyish sludge when removing oil filler cap..hopefully not..cheers Baz