So, after my E46 radiator expansion tank blew in spectacular fashion, the system has been fixed, refilled and bled.

Driving home from the Garage and about 20 mins into stop start traffic the Thermostat gsuge climbs up to 3/4, stops and starts to go down really slowly (estimated 10 mins back to normal). I “forced” it back in 30 secs but turning the interior heating on full blast.

I tested again later by leaving the car in the garage with all the same electrics on (aircon, lights, bonnet closed) and although no overheating occurred I notice the the front most fan (my BM has two, a rear fan and a more forward fan directly under the grill) never came on – presumably this is only for an overheat issue?

As the work was costly, could anything still be wrong? Could it have been some trapped air or something?[/s]

Any advice appreciated.

Thanks

head gasket gone ? – terminal event on my E39 🙁

possibly not properly bled – issue MAY have sorted itself by driving the trapped air into the expansion bottle ….
That’s what id hope for anyways 😉

Airlock. Bet you my bike(*).

(* – offers of bike-related stakes are fictional)

(offers in writing are legally considered formal)

scaredypants – everything else was fine, no lights on the dash etc, would that not manifest itself pdq?

There is what appears to be a bleed screw* to the right of the rad cap. I’m tempted to turn it when it all cools down and see if it releases anything.

* why else would there be a 1p size bolt shape screw there?

Note that I know nothing about beamers. Some of what you wrote might indicate air in the system. Does the rad need topping up?

Is there a sensor that switches your fan on and off? Somewhere in the radiator, with wires to is. Are the wires plugged in properly?

If you short them does the fan start working, but not otherwise? That sensor could be your problem.

Note that I know nothing about beamers.

Cover engine with plastic sheeting when cold and reverse jet wash the radiator, youll be amased at the amout of dead flies that fall out the front, also remove the tiop and bottom hoses and put a hose pipe on top hose entry on the rad and bung in a rag to seral around hose, then gently turn on hose and see all the crap flow out of bottom hose conection of radiator, try some rad flush as well.

mine did it once, no dash lights except temp the 1st time.

Nothing for a year or so

Major overheaty boiliness after a motorway run, no warning lights at all that time. Sorted by AA man who said probably HGasket, shoved in the chemical equivalent of a raw egg and bled out all the “air” in the system.

Got me to my weekend in the lake district, running fine.
Next time I started it (2 days later) major overheating and exploding plastic pipes in the cooling system (and only 300 miles from home 🙄 )

ENded up scrapping the car as the repair was going to cost more than the thing was worth

My first thought was head gasket. How does the oil look? Any mayonnaise appearance around the filler cap?

Airlock/blockage due to a collapsed thermostat?

My E39 V8 did this, and the only thing you could see was one of the hoses deforming due to the blockage.

Its a while ago since mine, but I do remember there are two bleed screws that need to be done in a certain order when filling / topping up (one on the rad and the other on the thermostat housing IIRC) to stop trapped air. Hopefully its something that simple.

I got to do this a process a fair bit as my 528 had intermittent coolant dumps (from the safety valve) – always the day after a long journey or being stuck in traffic. In the end it was diagnosed as a small crack in the cylinder head.

geoffj – Member
My first thought was head gasket. How does the oil look? Any mayonnaise appearance around the filler cap?

Nope, otherwise I will be scrapping mine too I guess.

To answer the fan question, it has two fans – the one nearest the block is always on, the one furthest away under the grill isn’t on but could only be used in overheat I guess.

Re the rad flush – done at the garage – becuase the cracked expansion tank occurred in there work shop after the Air con was topped up.

I’ll have a go at the bleed screws and see what happens.

I’ll have a go at the bleed screws and see what happens.

Could you not take it back to the garage and just get them to sort it – including taking it on a proper test drive, to check that all is well.

The two fans – One is for the A/C and will be permanently on when it is, the other is the radiator fan that switches in and out according to engine tempreature. Instead of just replacing the expansion tank, I’d be looking at why it failed? Faulty/stuck thermostat? These should always be replaced after a cooling system issue for the sake of a few extra £’s IMO (Vehicle Tech)

oink1 – they did replace the thermostat. They reckon that was faulty, which has over pressurised the system which is where the expansion tank comes into play. Its an original part on a 13yo car with 104k miles. Internet searching reveals its a weak / cheap plastic component on E46’s and is prone to cracking due to deterioration after age / use has taken its toll.

Thanks for the fan advice – turning the A/C off does indeed halt the inner fan.

geoffj – Member
I’ll have a go at the bleed screws and see what happens.
Could you not take it back to the garage and just get them to sort it – including taking it on a proper test drive, to check that all is well.

Unfortunately I picked it up at 5.30 and they close at 6 – and I’m off on holiday (not with the car) at 5am tomorrow – it’ll have to wait.

Have you noticed any drops in the volume of water in the expansion tank? i.e. when you picked it up it was at MAX but when you got home its dropped below that? Indicates an air leak that has cleared.
Keep an eye on the coolant level and top it back up to max when its cold.

Will check that bigyinn, thanks.

Right checked. The engine is still “warm” but… In the expansion tank (which has the filler cap on top) there is a float & rod. The diagram indicates if the rod is pushed anything more than level with the filler cap, its ok. Well, with the cap off, it was about 3″ above and shining a torch in I could see the float level with its “stop” and fluid under. I nudged the rod with my finger and the whole lot moves freely.

I also checked the Oil cap and dipstick, no sign of any gunk what so ever.

As previously suggested – find the radiator fan switch, remove the plug and short the two wires to check the fan cuts in. (The garage should have checked that though when they refilled the system, water pump? – have come across some horrific ones in my time with plastic impellers that disintegrate with time – old shape Mondeo V6 springs to mind!)

BMW e46 s need a specific bleeding process even with right technique sometimes takes three goes. I d try that if it still over heats try water pump and thermostat both easy DIY replacement

I’d go with an air lock too. It should have been bled properly and tested before handing it back to you really as it’s very easy to kill the engine as you know.