Help with car overheating

[toastybase]

I drove 400 miles for Christmas but my car has overheated. It's safely on the drive but I don't want to drive it to the garage.

I'm not sure what to do as o feel it's the water pump that needs replacing. Should I get aa cover and then get them to check it first?

It's a BMW Z4. 3.0si 2006

Edited by toastybase on Thursday 31st December 13:52

[davebem]

Have you checked anything? e.g. check the coolant level, check the electric fan is kicking in?

[wjwren]

is there a noise or squeal from engine? any water pissing out underneath? Whats coolant level like?

[toastybase]

The coolant level is good as well as the oil level. The fan kicked in as I could hear it running when I pulled over.

Car starts fine but I haven't driven it since.

I would just like to fix it without overpaying. Is it worth checking fuses?

Eta. No squeal or odd noises

[Monkeylegend]

Could be as simple as a sticking thermostat, assuming they still have one, or failing that the water pump.
If you run the car with the header tank cap off, does the water seem to be flowing/moving?

[toastybase]

Monkeylegend said:

Could be as simple as a sticking thermostat, assuming they still have one, or failing that the water pump.
If you run the car with the header tank cap off, does the water seem to be flowing/moving?

I'll try this. So do I just remove the cap and start the engine?

The temp gauge is now back down to cold (blue) so I would have thought that if it were a stuck thermostat it would immediately rise to red once the engine is on.

[Ozzie Osmond]

How do you know it overheated? Just temp gauge or big cloud of steam?

How's the coolant level? Correct, or has some been blown out by normal pressure or over-pressure?

If there's coolant in there the car should be fine to drive gently to a garage provided you aren't sitting in traffic and it's not too far to travel. Top up the system before you start if the coolant level is low. Use the bleed valves if necessary to avoid airlocks (if the pump is running in air the water won't move).

If, and this is a big if, it's a car with plastic vanes on the water pump and they've sheared off, the question becomes one of where the pieces have got to.... Hopefully that's not the case. I don't know what pump was used on Z4.

It is quite common for water pump wear to lead to a small leak down the water pump shaft. You may never see any "wetness" because it only leaks when the engine is hot and the system is under pressure. But because the engine is hot the leaked coolant evaporates off very quickly leaving nothing to see. When the coolant level drops far enough the pump is running in air and your car will overheat. This may well be what's happened to you. So carefully check and top up the system, then see how the car behaves. Keep a careful eye on that temp gauge until you find out exactly what the problem is. [Suddenly joining AA is unlikely to worthwhile because, amongst other things, you haven't broken down!]

[Krikkit]

toastybase said:

The coolant level is good as well as the oil level. The fan kicked in as I could hear it running when I pulled over.

Car starts fine but I haven't driven it since.

Chances are it'll be water pump or sticky thermostat then. Given how easy it is to change the latter I'd do that first. Is the water pump aux belt powered on that engine?

[Ozzie Osmond]

Thermostat usually fails "open", not "closed", for engine protection. I'm told they can sometimes fail closed though. One way to protect your car in that case is to drive the car gently with the cabin heater on full blast.

Standard practice on BMWs is to change water pump and thermostat at the same time. If they haven't failed yet, they will eventually!

[Ozzie Osmond]

Note: If you have an airlock the coolant header tank can appear to show "full" even when a lot of coolant has gone missing. If as soon as the engine warms up the cooling system starts hissing and fizzing you've probably got an airlock. Switch off IMMEDIATELY and let things cool down - then bleed the system.

If a BMW is being a real pig to fill you can open a bleed screw, put you mouth to the header tank and blow gently into the system. Once the air is purged coolant will begin to emerge from the bleed screw valve. Once that happens, quickly tighten the screw. If you are doing this, proceed carefully to make sure the header tank doesn't get completely empty - or you'll be blowing more air into the system.

[Monkeylegend]

toastybase said:

Monkeylegend said:

Could be as simple as a sticking thermostat, assuming they still have one, or failing that the water pump.
If you run the car with the header tank cap off, does the water seem to be flowing/moving?

I'll try this. So do I just remove the cap and start the engine?

The temp gauge is now back down to cold (blue) so I would have thought that if it were a stuck thermostat it would immediately rise to red once the engine is on.

Make sure the engine is cold before you remove the filler cap, it will be underpressure when it is hot. A cold engine will take a while to heat up so it won't go straight from blue to red.

[toastybase]

Monkeylegend said:

toastybase said:

Monkeylegend said:

Could be as simple as a sticking thermostat, assuming they still have one, or failing that the water pump.
If you run the car with the header tank cap off, does the water seem to be flowing/moving?

I'll try this. So do I just remove the cap and start the engine?

The temp gauge is now back down to cold (blue) so I would have thought that if it were a stuck thermostat it would immediately rise to red once the engine is on.

Make sure the engine is cold before you remove the filler cap, it will be underpressure when it is hot. A cold engine will take a while to heat up so it won't go straight from blue to red.

Ok thanks for the above advice. Ive check this morning and the coolant level is now very low (nothing in there).

It was full when I left the car previously.

So just to recap;

Temperature needle shot up to red
I limped back and parked up
Now engine is cold, I checked coolant and it's all gone

I would really like to diagnose this myself as much as possible before taking it to the garage this week. I then need to make the 400 mile trip home for work this week.

Edited by toastybase on Sunday 3rd January 14:24

[Monkeylegend]

You clearly have a significant leak so I would check the coolant header tank, they are known to leak on the Z4.

[lostkiwi]

First step is to refill with coolant (water will do at this stage).
Run it up to temperature on the drive and look for any signs of water leaks.
Allow to cool, and recheck coolant level. It may be low as there may be air introduced into the system which it will pump out into the header tank. Repeat above again twice more. If coolant level is stable take for short drive. Allow to cool and recheck coolant level again.

It may be the coolant level dropped without you being aware (when was the last time you checked it?).

You can also buy UV leak test kits on ebay. This is added to the coolant and the engine run. Check at night with the supplied UV torch and the leak will clearly show up.

Edited by lostkiwi on Sunday 3rd January 18:35

[Who me ?]

toastybase said:

Now engine is cold, I checked coolant and it's all gone

I would really like to diagnose this myself as much as possible before taking it to the garage this week. I then need to make the 400 mile trip home for work this week.

Edited by toastybase on Sunday 3rd January 14:24

What is state of oil- is it clean or gungy. if it's clean, then it'd be safe to assume that there's no path between water and oil- so you have a leak, perhaps a head gasket failure, but no oil /water contact. Could be as simple as a hose leak.
Naughty, but some of the larger breakdown blokes don't care. Most relay services insist on a 24hour period before you access them. But do it now. Some quote by car make & age.

[james_gt3rs]

Chances are it's the radiator leaking. I assume it's mounted quite low, so vulnerable to the elements. I'd top up with water than just leave to idle until up to temp, and check for leaks under the car. If you managed a 400 mile drive then it's probably a small leak (for now)

[Spangles]

A mobile mechanic may be the safest option.

[lesstatt]

Back to school tomorrow eh

[Trixxz]

Ahhh self repair of BMWs - Heres some handy links for you so you can poke around with some semblance of knowing where things are.

Interestingly, It seems you have an electric Waterpump that doesn't look too complicated to replace if needed. Anyway have a look.

Waterpump and Thermostat - http://www.realoem.com/bmw/en/showparts?id=DU52-EU...

Hoses and Locations - http://www.realoem.com/bmw/en/showparts?id=DU52-EU...

Back when I owned BMW's I used the part numbers off that site and my local dealer located the relevant parts on their system.

Good luck!

Edited for Shpelling

[boz1]

lesstatt said:

Back to school tomorrow eh

Let's hope you are.

toastybase said:

Ok thanks for the above advice. Ive check this morning and the coolant level is now very low (nothing in there).

It was full when I left the car previously.

I think this just means that when you first looked shortly after parking up, that was before the engine had cooled and all the air in the cooling system had worked its way to the top of the system (or the coolant subsequently continued since to drain out of whatever leak has arisen in the system). Also, in case you are not aware, never take the radiator cap off when the car is fully warm because you will likely get a face full of boiling steam...

toastybase said:

So just to recap;

Temperature needle shot up to red
I limped back and parked up
Now engine is cold, I checked coolant and it's all gone

I would really like to diagnose this myself as much as possible before taking it to the garage this week. I then need to make the 400 mile trip home for work this week.

There's only so much you can diagnose yourself without some equipment, or without running the car, which risks overheating it again. However, if the electric water pump runs on ignition only (i.e. engine not running), then you could potentially top the system up and look for leaks.

Other than trying to visually sight which components has failed (could be radiator, hoses, water pump or thermostat), it's going to be hard to diagnose on the driveway without some dye and a system pressure tester.

Do not try and limp the car anywhere else however because you will risk overheating it again and there is a major risk on these engines that you will blow the headgasket. (Hopefully, that has not happened as a result of the initial overheat, given that you pulled over when the temperature rose.)

If you like the car, take it to a garage and let them fix it properly. Clearly, it is not a good idea to start trying DIY when you are stressed about the breakdown and under a time constraint because you need to use the car again.