BMW 525i -- August 27th, 2005

Wow. It's been a long time. Spiders have made homes in the parts on the garage window sill.

The battery has gone dead and requires an infusion of energy.

Why the delay? Well, that's a thing. Note the following box:

A head arriving? No, that's a head packaged up to return whence it came. A day or two after my last report -- which would have been the end of June -- I phoned around and located a dismantler that had a used head for a reasonable price. BMW M20B25 heads are common and easy to find, but the prices usually range from staggeringly unreasonable to eye-poppingly ludicrous, so I was pleased to find a place that would courier one to me without shrivelling my wallet.

Head #1

The head arrived in two days, in the box you see above. Yay! I opened it eagerly and... It was the wrong head. It was a head for a 520i or a 320i. So, as you can see above, I sent it back and asked for the right one this time.

Head #2

What I got, after a few days, was just a head casting, not a whole head. No camshaft, no valves, no rockers. Okay, fine, I can move those over from my old head, but... The casting was cracked. I phoned the dismantler. Turns out those were the only heads they had, but more cars were coming in all the time, so maybe they'd have another soon. I told them not to bother; I'd find one elsewhere.

Head #3

Sure enough, I found one on eBay. The seller had 100% positive feedback and claimed the head was straight and not cracked. I bid and won it. What arrived was warped and cracked. Bleh.

So I called the dismantler again. By now they had more heads. Yay!

Head #4

It was starting to get ridiculous. This head wasn't cracked, but had suffered such profound corrosion that the water passages had eroded into the combustion chamber sealing surface. Useless. I was beginning to suspect that the dismantler's technical skill begins and ends with making counter-clockwise wrench noises, and evaluating the results for applicability, quality, and general lack of damage was far beyond their diagnostic skills. I phoned and said I would come up to (a) return their latest offering, and (b) pick a head for myself.

Head #5

Fortunately, the dismantler is only an hour from here. I drove up, found the place, and handed over the bad head. Before I could point out the flaws, the fellow picked it up, asked me if it was the bad one, and when I agreed he heaved it, with gusto, through the open window of a nearby E30 320i that was being used as a trash bin. Then he brought me my new head, which turned out to be in excellent condition. At last! Here it is:

Now we line up parts and tools. Note certain key ingredients, such as a rubber mallet and various seals and gaskets including a new head gasket. The spark plugs came out of the new head. They're almost new but they're NGKs, so I ordered proper Bosch plugs.

Here's a box of new bits, such as a coolant hose, the new spark plugs, a new distributor cap and rotor, new head bolts, more gaskets, and various bolts, nuts, and washers.

We need various vital fluids such as antifreeze and distilled water to make up the coolant, regular dinosaur juice to run on for a few days until I'm sure everything works, and synthetic oil for the long term. Note the handy fire extinguisher, in case it all goes horribly wrong.

Here's a final view of the engine innards, prior to installing the head. The deck has been scrubbed, and the threads have been cleaned with a tap.

The following picture is a closeup of the front of the engine, in case you were wondering what it looked like. The water pump will cover the big hole.

There is a pipe that runs vertically between the head and the block to allow oil to drain back to the sump. It's held in place with a spring, which makes it awkward to install. I used an easy trick to install it. I compressed the spring with a cable tie, as you can see in the following picture. Once the head was installed, I simply cut the wire tie and allowed the spring to pop the pipe into place. Neat.

Here is the engine block, with the head gasket and new dowel pins installed.

At this point, my hands were too dirty to work the camera. Assembly, as they say, is the reverse of disassembly. It went back together easily, and this is the result:

And now the moment you've all been waiting for: Does it run? Does it?

Yes, it does. The idle is even and smooth and it revs nicely. M20 engines aren't exactly silent -- the valve train has no hydraulic damping and relatively large clearances, and the injectors tick loudly, but it sounds good.

Initially, it wanted to overheat, but that was easily cured by a quick jaunt to the local BMW dealership to obtain a new thermostat. Now I wouldn't say a BMW thermostat is cheap. In fact, I rather suspect the average BMW dealership funds their entire parts department on thermostat sales. After the head and a new distributor cap, the thermostat was the third most expensive individual component I had to purchase. Still, a new thermostat is far cheaper than a head replacement, and it was pretty obvious that the bad thermostat is what overheated the car and killed it. Why would the previous owner keep driving an overheated vehicle? Did he hate his car? Did he think he could go just one more mile? Did he not hear the warning gong to tell him the engine was overheating?

This car has a "Check Warning" system. If it detects that you've opened door with the lights on, "Lights On?" will appear on an LCD panel in the instrument cluster. The display will also give you warnings of other things, like telling you you're low on washer fluid, or that the brake lights have burned out, or that you need to add engine oil, or that the engine is overheating and about to self-immolate the head. Whenever a warning appears, you're supposed to hear a loud "Bong!" But the gong wouldn't bong. It was mute.

I had a spare bonger that came with a batch of other parts, so I figured I'd try it. It goes under the dash, here:

The gong is the cylinder with the bundle of wires. Remember the mess of wires that used to be in there? I sorted all that out, and the new bonger bongs. Yay!

The hole in the dash didn't really suit the freshly cleaned interior, so I installed an inexpensive (on sale at Halfords) Radio/CD player.

Initially, the radio part of the new player didn't work because the antenna lead -- a cheap solid-core coaxial cable -- had been moved, crimped and bent a few too many times and was internally broken in several places. I patched it, and now the radio works.

Another minor problem: The warning system kept complaining "Coolant Low" even though it wasn't. With the freshly repaired gong now loudly voicing this problem at every opportunity, it was starting to get irritating. Since the cooling system was obviously full, there had to be a problem with the sensor.

The coolant level sensor lives in the bottom of the coolant reservoir tank on the left side of the radiator, and consists of a hollow donut-shaped float that rides on the outside of a sealed tube. Inside the tube is a magnetic reed switch. The float contains a tiny magnet; when the presence of water lifts the float to a certain point, the reed switch closes to tell the system that there is coolant in the radiator. Simple.

An examination of the sensor revealed that the float was missing. At some point, it must have popped off (it's restricted only by flimsy plastic tabs) and bobbed to the surface of the reservoir, at which point the mysterious object was probably fished out and discarded.

Luckily, I have a spare radiator -- it came with a batch of parts -- with a sensor. Unfortunately, it was damaged -- a pin was broken off. But, it had a float, so I tried the new float on the old sensor.

And it didn't work. Now at this point, most reasonable folk would simply have put the sensor back in and jumpered the sensor leads. It's not like this is an important sensor. It sits at the bottom of the reservoir, so at best it's only going to warn you the cooling system is almost empty if you're blind to the pool of antifreeze on the driveway, or if you're on the motorway, after the engine has overheated to incandescence. It's not exactly an early warning sensor, in fact it's more of a way-too-late sensor that probably reports its own lost float more often then it reports an empty rad.

Jumpering the sensor leads... As I said, that's what most reasonable folk would do. I'm not reasonable. At this point, I decided I was going to make it work, by God, and I was going to do it without spending a penny on new parts.

First, I needed to find out why the sensor didn't work. The innards are held in with an O-ring and some soft glue, and popped out easily. It was immediately apparent why the sensor didn't work. The entire guts had simply corroded away. The glass tube of the reed switch was the only thing left, but its leads were gone. I guess over fifteen years, enough road salt and moisture had worked in to completely dissolve the works.

Luckily, the broken sensor from the spare rad had good innards. You can see the difference below. The broken sensor with the good guts is on the left, the unbroken but innard-less sensor is on the right. I've already polished the soldering tabs in anticipation of moving the innards from the one on the left to the one on the right.

Here's the repaired sensor innards, with a wire to replace the long solder tab that had dissolved. The plastic looks chewed because I had to cut away some of it to expose the tab.

This is the completed sensor. The plastic tabs that keep the float from floating away were marginal, so I used the soldering iron to heat a loop of paper clip wire and melted it into the top of the sensor tube. Success!

Finally, the result! It's been insured, taxed and tested. I had the testing station put in a new rear exhaust box and replace some corroded brake lines. There are still some cosmetic issues and a few minor quirks, like a leaky windshield washer tank and soft rear subframe bushings that sometimes give the rear a waggly feel, but the handling is devastatingly good and is capable of safe cornering velocities that would shame a slot car. The ride is smooth and comfortable, but sports car taut and precise. Power is ample, and the brakes wipe out all concept of speed with an ease, control, and quickness that is unlike anything else I've driven.

Quite simply, this is the most staggeringly impressive car I've ever owned.