520i temp gauge/overheating?
 

Hi - hope someone can help with this. I'm new to this group so
apologies if this has come up before, but I couldn't find the same
problem described.

I have a 520i (P reg UK) and last night as I was driving home, I
noticed the temp gauge go into the red zone (where the red light came
on, which is what made me notice). I thought the engine was overheating
and was about to stop, but when I took my foot off the accelerator it
went back down to 'normal' temp. I wouldn't have expected this if the
engine was genuinely overheating (e.g. if the fan belt had broken or a
hose had burst) - in that case I would expect it to stay hot until I
switched off. I continued to drive home slowly (only a couple of miles
in all), and this behaviour repeated itself a couple of times.

Does anyone know what this could indicate? Could there be a thermostat
problem? I was hoping someone would recognise the symptoms and be able
to advise.

Thanks

Flummoxed

520i temp gauge/overheating?
 

When I blew a headgasket on my 735, exhaust got into the cooling system.
what would happen, tho not as rapidly as you are experiencing; would be the
engine would be hot (indeed, overheating) becuase the air was at thermostat,
preventing the coolant to circulate and the temp to raise to the "danger" mark.

If I QUICKLY raised teh rpm or dropped it it seemed to inject enough <something>
so make the coolant circulate again and coolant from teh radiator would hit the
temp sensor/thermostat & then the temp would drop (only to raise again later)

How's your coolant level?

On 18 Apr 2006 01:28:27 -0700, "Flummoxed" > wrote:

>Hi - hope someone can help with this. I'm new to this group so
>apologies if this has come up before, but I couldn't find the same
>problem described.
>
>I have a 520i (P reg UK) and last night as I was driving home, I
>noticed the temp gauge go into the red zone (where the red light came
>on, which is what made me notice). I thought the engine was overheating
>and was about to stop, but when I took my foot off the accelerator it
>went back down to 'normal' temp. I wouldn't have expected this if the
>engine was genuinely overheating (e.g. if the fan belt had broken or a
>hose had burst) - in that case I would expect it to stay hot until I
>switched off. I continued to drive home slowly (only a couple of miles
>in all), and this behaviour repeated itself a couple of times.
>
>Does anyone know what this could indicate? Could there be a thermostat
>problem? I was hoping someone would recognise the symptoms and be able
>to advise.
>
>Thanks
>
>Flummoxed


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520i temp gauge/overheating?
 

>How's your coolant level?

I checked the level and it was low - I put about 0.8 litres in to bring
it up to the "Cold" level. Does anyone know if that would be low enough
to cause the effect I described?

(Of course the question remains as to why it was low, but it could be a
long time since I checked the level. I couldn't see any obvious signs
of a leak, although I've yet to drive it since I topped up the cooling
system).

Thanks

Flummoxed

520i temp gauge/overheating?
 

Did you bleed the system? or just top it off?

If there's air trapped in the system, topping it off won't fix it.....


On 18 Apr 2006 12:46:15 -0700, "Flummoxed" > wrote:

>>How's your coolant level?
>
>I checked the level and it was low - I put about 0.8 litres in to bring
>it up to the "Cold" level. Does anyone know if that would be low enough
>to cause the effect I described?
>
>(Of course the question remains as to why it was low, but it could be a
>long time since I checked the level. I couldn't see any obvious signs
>of a leak, although I've yet to drive it since I topped up the cooling
>system).
>
>Thanks
>
>Flummoxed


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520i temp gauge/overheating?
 

Ooerr, good thinking. No I didn't bleed it, I don't know how to at the
moment. I'll have to look it up.

Cheers

Flummoxed

520i temp gauge/overheating?
 

Had a similar problem witht the bizarre temperature guage problem, mine
lasted like a day and then disappeared. It was followed a week later by
the engine cutting out problem which was diagnosed as a faulty cam
position sensor. During the replacement of the sensor, the mechanic
discovered that the thermostat housing was broken. The
thermostat/housing might be what's causing your problem..

520i temp gauge/overheating?
 

In article .com>,
Flummoxed > wrote:
> I checked the level and it was low - I put about 0.8 litres in to bring
> it up to the "Cold" level. Does anyone know if that would be low enough
> to cause the effect I described?

Could well be. The temp gauge on these cars isn't a straightforward
thermocouple device that gives a true read out of the temp. It appears to
work like one, but in fact the ECU will keep it in the middle over a wide
range of actual temperatures that are within the normal running ones.
Exceed that and it goes up very quickly.

Under normal conditions these engines don't need topping up between
services.

First thing to check is that the fan clutch is working - it progressively
'locks' up when it senses the airflow through the rad getting too high and
runs up to a higher maximum speed. Only usually at town speeds and you can
hear the increased noise from it.

As regards a leak it's often the water pump and difficult to detect
without a dye/pressure test. But get the engine up to temperature and then
stop it. Squeeze the top hose after a couple of minutes. It should feel
pressurized. If not - ie it squeezes easily you've got a leak.

> (Of course the question remains as to why it was low, but it could be a
> long time since I checked the level. I couldn't see any obvious signs
> of a leak, although I've yet to drive it since I topped up the cooling
> system).

If it turns out to have a leak and it is the pump get the thermostat and
housing changed at the same time - and also the serpentine belts unless
you know when they were last done. They're not as expensive as the labour
to have them done later.

If you say where you are in the UK you should get some recommendations for
specialists. You might also consider joining the group in my sig for E39
expert advice.

--
*Friends help you move. Real friends help you move bodies.

Dave Plowman
528 Auto London SW12 (UK)

Co-Moderator BMW E39 Enthusiast Group http://groups.yahoo.com/group/bmwe39

520i temp gauge/overheating?
 

Thanks ChrisJ and Dave for the further advice/help, and the pointer to
the other group. (I didn't even know my car was an E39, just to show my
ignorance).

I've done nothing further yet to the car as I've been too busy, but I
will want to sort it out soon.

I'll report back once I've had a chance (hopefully by the weekend) to
look into it.

Cheers

Flummoxed

520i temp gauge/overheating?
 

>Could well be. The temp gauge on these cars isn't a straightforward
>thermocouple device that gives a true read out of the temp. It appears to
>work like one, but in fact the ECU will keep it in the middle over a wide
>range of actual temperatures that are within the normal running ones.
>Exceed that and it goes up very quickly.

are you 100% positive about that? I had heard that before, that the guage
really is more of an "idiot light" made to look like a guage.

Yet; when I put a cooler thermostat on my car, the guage absolutely settles a
touch lower than it used to.

>without a dye/pressure test. But get the engine up to temperature and then
>stop it. Squeeze the top hose after a couple of minutes. It should feel
>pressurized. If not - ie it squeezes easily you've got a leak.

Unless he's got a headgasket leak where exhaust gases are getting into the
cooling system -- then it would indeed still feel pressurized.

Of course, those are based on my experiences and not specific technical
expertise

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520i temp gauge/overheating?
 

Josh Assing wrote:

> are you 100% positive about that? I had heard that before, that the guage
> really is more of an "idiot light" made to look like a guage.
>
> Yet; when I put a cooler thermostat on my car, the guage absolutely settles a
> touch lower than it used to.

Yes, BMWs are actually sensors and meters (not switches like idiot
lights) but the display is non-linear such that middle part of the
display represents a much wider variation of temps than the sides. The
intent was to keep owners from complaining about small (normal)
variations in temperature.

--
-Fred W