E60: Opening Stuck Bonnet.

PROBLEM:
The annoying turbo whine from my previous post can only be heard while underway and not while stationary, so the bonnet is up and down for every bit of work and test drive. After several such runs, the O/S (driver's side) bonnet latch refused to open. Nearly an hour was spent with a helper pulling the bonnet-lever while I tried to push / pull / wiggle the O/S bonnet up, but it was stuck solid. The front bonnet lip on the E60 (and all modern BMWs) extends right down over the slam-panel / grille and the latches are a good 6 inches up inside it. It's impossible to slide something up through the gap between the rubber seal and pop the latch from outside, as you can with older cars, so I turned to the internet and eventually found a superb solution.

CAUSE:
Yes, this is quite a common problem with the E60, especially when you are working on it at home. The cable splits in two and a separate one runs to each latch. The end of the cable fits through an eyelet on the 'release-switch' and is kept under tension by a plastic collar that fits into a notch in the latch-frame. If the plastic collar pops out of the notch, cable tension is lost and the bonnet-lever simply will not pull the release-switch far enough. Removing the bonnet-lever reveals a plastic-cage with the cable housed deep inside, so yanking that further with a pair of grips won't do either. If you've been working on the front-end of the car and changed the location of the bonnet-latches / slam-panel, even slightly, then there's a high chance the collar will start popping out.

SOLUTION:
There are a few forum threads saying the latch can easily be opened from underneath the car, with the front under-tray removed. This is true, but the E60 engine-bay is so tightly packed there is a bit more to it than that. I have to give props to Kilty1 on forum.BMW5.co.uk, for his amazing guide, linked below:

http://forum.bmw5.co.uk/topic/87159-bonnet-release-not-working/

Getting to the latch requires removal on the front under-tray, both pieces of the O/S brake air-duct and the plastic inlet-pipe that runs to the air-filter. These can all be removed from underneath the car, as shown in Kilty1's guide. He used ramps, though I managed to open mine with the car raised a few inches on an axle-stand. Looking up with a torch, you will just see the latch next to the inner corner of the headlight.

Luckily, my brake duct, inlet pipe and tray were already off as I was working on the car, so I could get straight to the latch and will just show a couple of steps and pics from Kilty1's guide:

1. Reach up and slide a steel-rule or similar slim/flat object into the bottom of the latch, just to the inside of the right-hand spring-wheel [shown on the left in the pic, looking from front]. When the steel-rule is far enough in there should be a small clunk. Now slide the steel-rule quickly out and the bonnet latch should release on the O/S. 

2. The collar doesn't take much to pop out, so to stop it from happening again as soon as you shut the bonnet, wrap a cable-tie round the back of the collar and round through the gap in the steel-frame. It will be solid.

Does an early '80s E21 316 with an M10 run on unleaded fuel?

The answers before I bought the car pointed to yes but it turns out that the four-cylinders might not after all. Ignition timing is fine, apparently, down to as little as 92-octane unleaded fuel, but valve wearing is still a problem and an additive is recommended. It's about £8 a per tank so could be expensive over time. I don't reckon the previous owner had been putting any in regularly or they would have given me half a bottle with the car, so I think I'll be taking my chances.

The other thing is regular 95-octane unleaded or 98-octane super. The engines are designed for 100-octane leaded petrol so regular unleaded might be a fair drop performance wise, but does it make a difference to the valve wear?

As we parted company the previous owner said to fill it with super to get the best out of the engine, but said it would run fine on regular and that was all that was available to me at the filling station so it had to do. The car charged home without a grumble from the engine and feels very lively indeed, though I'll be filling it with super next and see if it makes any difference.

UPDATE: It turns out my engine has had the hardened valve treatment so it can run any unleaded without excessive top-end wear, so I haven't needed any costly, annoying additives and that's a relief. The engine seems happier starting up and a bit livelier running on 97/98-octane petrol, which is what I've been using for the infrequent use the car gets. Obviously the power gain isn't vast on a 100bhp engine and super-unleaded is dear stuff, so now I'm starting to use the car a lot more I'll be switching back to 95 RON for the sake of economy.

Fuel Consumption:

I've worked out from averages that my late 316 M10 1.8L engine, running a Weber DMTL carb. and the 5-speed 'sport' gearbox is giving me ~26mpg, which isn't bad at all really. Using the lower octane 95 RON fuel may give better mileage, or may make it worse, either way I would imagine the difference will be negligible given the amount I drive the car.