M40 running issues

[Gravy]

Hi all,

Soory for the long post but I have a problem with the running of my M40 and would like to know if any of you can diagnose it before I pay money for parts I don't need!

Initially my temp gauge only just got out of the blue zone even when running from hot - so I changed the blue temp sender and flushed the coolant and refilled with fresh.

Immediately after I did this, and ran the car, she ran the temp into the normal zone of the gauge and the cooling fan came on! - Brilliant I thought, problem solved.

Nah uhh!

I went for a 20 mile run and she never got out of the blue zone again. Then when I ran her to work the next day I checked under the bonnet for coolant loss before leaving and the fan was running straight away, and took an hour to reach normal temperature on the gauge which was 10 minutes of motorway driving and 50 minutes of idling?? If she is left to idle after running, the gauge needle climbs, hits the quater mark then flickers rapidly between that position and normal!!
And now today, whilst travelling to play rugby and then coming back again, two problems have occurred.

The first is, that for 3rd gear and fourth gear (not sure about 5th as I don't have a chance to explore on this trip) is that the car will accelerate normally up to just over 4000rpm, then its like its hit a brick wall or limiter and even sounds like its not firing all cylinders, and will not climb any higher up the range.

However sometimes if I keep it pinned it will very slowly climb and clear itself and then it will suddenly realise what i'm asking it to do and will kick in with the correct accelerative feeling again.

Finally, on cold start up I have a strong smell of petrol that lasts for about 5 minutes and then disappears.

I have a feeling I'm looking at a number of easily remedied problems but I would like some advice please guys cos its really annoying me, it hasn't run right since I bought her last September.

I'm thinking, thermostat, water pump, dodgy gauge sender, and blocked fuel filter or fubar'd pump?

Any input would be very greatfully received, thanks in advance!

Robbo

[RevBillyG]

If she is left to idle after running, the gauge needle climbs, hits the quater mark then flickers rapidly between that position and normal!!

I had that too. I took the dash out and tightened the bolt on the back of the temp gauge. That sorted it.

[320Touring]

with regards to the revving problem

the m40 can suffer from worn camshaft lobes if the oil spray bar gets clogged up-

take the rocker cover off and have a good look.

other sources could be rotor arm/cap?

[Brianmoooore]

Changing the blue temp sensor wont do anything for the running temp of the engine, or what the gauge reads.
The gauge works from the brown temp sensor, but I doubt if there's anything wrong with that either.
First thing to do is take out the instrument cluster and tighten the small nut on the back behind the temp gauge. This should stop the gauge jumping around and make it read accurately, so that you can see if your car really is running cool.
If it is, then change the thermostat. The bridge bar on BMW OE ones frequently breaks, leading to cool running.
For the "brick wall" at 4000 RPM", check out the plugs. They may be sooted up from running rich because of the cool running.
Cam wear on the M40 can give a 4000RPM rev limit, but this is unlikely to happen suddenly. More likely the distributor cap and rotor could do with renewing.
Don't change the leads. Never seen a dud OE one.

[Gravy]

Cheers for the help, I shall take on all advice and action it as soon as I can this week! I really hope it will run right soon as the engine has been well looked after according to the history, and it doesn't apear to be a nosiy as some I've heard!

I'll report back if the above mentioned remedies work!

Cheers