Why I don't check my tyre pressures myself ...

The twin rears on 660/670/700 vans are basically truck wheels and tyres. After 20 years of ownership, I learned the hard way, and I gave up checking my tyre pressures myself years ago . And as for punctures, which are rare, I just limp on 3 rear tyres to safety (front blowouts are different, you should only limp the absolute minimum on the rim - you will ruin the tyre), and then call out breakdown and let them take care of it. I have never successfully managed to undo the rear nuts by hand - they are torqued up with airguns by the fitters and almost impossible to remove with a hand lever/wrench. The other problem is that the supplied bottle Mercedes jack is barely adequate, and is only really usable in absolutely perfect conditions. Most 410D based Hymers are fully loaded at the back - just look at that rear overhang! - and after 25 years the rear springs are tired, making it almost impossible to jack up the rear. So why bother ... that's what breakdown is for. A trolley jack makes short work of it, but who wants to carry one of those?

As for checking the pressures - It is a complete pain in the bum to remove the trims if you have them, and then find an air hose with the right angle nozzle. 90% of all service area air pumps, especially those horrible coin operated ones, are useless - they won't get anywhere near 65psi. And in inexperienced hands you can let out more air than you put in - again I learned the hard way!

Every 3 months or so I just stop by ATS Commercial and ask them to check all my pressures. I always offer to pay, and they never accept. What I have found is that the pressures stay constant for ages and ages, and I have never had a slow puncture. I just drove 5000km over 5 months down Italy and Sardinia, and when I finally called into a garage because I caught a (very rare) puncture in the front, when they checked the rears they were spot on.

I also have the habit of regularly just bending down behind the van, so I can see how the twin tyres sit on the road, every time I fill up, especially on a long journey. You soon get used to the profile, and then you can easily tell if a tyre is going flat.

Of course this is just my personal preference - I am getting on a bit, so anything for an easy life! There is no reason why you can't carry a decent 12v compressor and the correct nozzle, or even a better jack. But new owners should take note - maintaining the pressures and changing tyres on the rear twin wheel Merc Hymers isn't as easy as on a normal family car.

Charging your devices - why not to buy Chinese inverters.

I often get asked about inverters for charging mobile devices - what is the best way? 12v adapters or use an inverter and just plug in the original charger.

If the device is a usb device - phones etc, then fitting 12v USB points is quite easy, they look pretty swish when compared with festoons of wires from cigar plug adapters. Many Hymers have small 12v sockets that look like small cigar sockets, but in fact are quality Hella 12v sockets, and if these are conveniently placed you can use these with USB adapters.

But for anything else that isn't USB, and comes with a black 240v charging block, then it's usually easier to use a small inverter.

Inverters are fine when in use, but they do have the disadvantage that they consume a small amount of power, when switched on doing nothing. You can minimise this by buying a top quality one such as a small Victron. Their entry level 180w model consumes 2.6w under no load, but still on and ready. This is equivalent to 0.2ah which means that leaving it on overnight for say 10 hours, will consume 2ah of your battery, which isn't that bad.

But some of the big Chinese inverters are shocking in this respect - they don't even quote a zero load figure - you have to measure it. I have seen big inverters chewing away through an amp or more, just when switched on doing nothing. On a cloudy day of wildcamping this would be a serious amount of usable power, lost for no good reason.

You simply don't need a 1000w inverter in a van, unless you actually intend to use it - ie a mixer, toaster or hairdryer - and in this case you have to back it up with battery and cabling capable of delivering 100amps! Small inverters are much more efficient, and the Victron is the most efficient for the money. Their 180w model will power a laptop, games consoles and as many phones and pads as you want.

I do keep banging on about Victron inverters, but they are the best for the money. Here is the datasheet.

https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-180VA-1200VA-EN.pdf

How the SOG toilet system works

Many old vans are fitted with SOG cassette toilet systems by previous owners, but unlike the standard cassettes they are not maintenance free, so if you have one it is important to know how they work.

How it works is this. On a non sog system - ie the original Thetford unmodified system, when you slide the cassette into the toilet, an air vent on the cassette is depressed which allows air to flow in and out. This is to allow equalisation of pressure as you go up and down mountains - without this, there could be unwanted venting of air when the flap is opened after a change in altitude. The blue chemical is used to control odour.

On a sog system, the cassette is modified to disable this vent to make it permanently closed. Then a hole is drilled in the outlet pipe, and a tube is attached, which runs to an extractor fan, and then to the filter panel mounted in the door. On some vans there is a conical filter rather than a door panel filter. This filter contains a charcoal filter, which is supposed to clean the air so that it doesn't smell when expelled to the outside. This filter is a consumable and should be changed regularly - how often depends on how much it is used, but for an average holiday van - once a year is generally about right. 

When you open the flap on a sog system, the fan is activated, by the same switch that activates the pump, and draws air down through the main flap opening - ie where you poo, and out through the pipe and fan and filter to the outside. This prevents foul air from rising up from the contents into the bathroom. When the flap is closed, the fan cuts out, but the cassette contents are properly vented because of the pipe, and therefore safe during altitude changes.

A properly installed and maintained sog system does not need the blue chemical, but with the caveat that when you empty the cassette, it does tend to pong more than if there was blue chemical added. Basically it is more eco friendly - so the theory goes.

When emptying the cassette, the procedure is to pull out the air tube from the cassette, and plug the hole with a  plug which should be stored in the toilet compartment. It is most important that you don't mislay this plug, in fact it is best to keep a spare, they have an annoying habit of coming out and disappearing down the disposal hole. 

The potential problems with sog systems - especially those fitted in older vans are as follows. 1. A previous owner has replaced the cassette with a new one, not knowing that the cassette has to be modified. 2. Over the years the wiring fails and the fan stops operating. 3. The charcoal filter never gets replaced, resulting in foul smelling air outside. 4. The procedure for removing and emptying the cassette is slightly more complex because you have to unplug the air pipe, plug the hole, empty, then the same procedure in reverse. You generally get a bit of a dribble which you have to be willing to clean. A pair of gloves and a packet of baby wipes stored in the toilet compartment makes the whole procedure as pleasant as possible.

In my experience of 20 years, and I am now a full timer, the sog system works well, and for full timing can save you around £20 a month in blue chemical. But even with all this technology installed it can still tend to pong a bit in hot weather, and I have found myself still using a bit of chemical now and then - I also use the cheap washing machine capsules from Lidl. However we tend to do a lot of wildcamping and use the cassette to the max quite often. If you use sites nearly all the time, where you can empty the cassette regularly before it gets full, then this problem is minimised. I also think that for heavy users, a new cassette every year is a good investment - a well used cassette, several years old, will eventually pong regardless of how much you rinse it out. My advice to buyers of old vans is always to buy a new cassette!

However, because there are a lot more components to the sog system, it does tend to need to be kept in working order, and to do this you need to know how it works. So for this reason I believe that for normal holiday use in the northern european climate, the case for a sog system is 50/50. But if you are an eco / anti chemical warrior, then sog is the only way to go.

This is the vent that is modified

Classic Hymer bathroom light column switch

The switch at the bottom of the classic 4 bulb lighting column is a generic SP60 single pole single throw latching switch with a white button. 25mm hole. Manufactured by Molveno (and probably others).

Once you know it's an SP60, searching with Google is easy. Search for SP60 switch white.

Cost under a fiver.

If your lights flicker, then a new switch should cure it.

You can also take out the switch and rinse the whole thing in brake cleaning fluid, or switch cleaner, or any other aggressive solvent. There are holes in the side of the switch which allow access to the insides - which is probably why they start to get dirty after 20 odd years of use.

Truma heater not working?

The Truma 5002 and it's similar siblings are fitted to most Classic Hymers. After many years of good service, eventually they can refuse to light. The fix can be quite easy if you know where to look.

This is how it should work. You push and turn the knob 23. This operates the gas supply and also an electrical switch in the base - 29. This closes the circit in the two switching wires 28, that go to the ignition unit 19. This generates a spark, which goes down wire 42 to the igniter electrode 41. When the fire lights, a flame sensor allows the gas to keep flowing and cuts out the igniter switch so that the ticking stops.

The first thing you need to do is remove the cover - lift and pull forward. Then you need to  look for a small plastic box at the lower left - this is the igniter unit - item 19 in the drawing.

Operate the control knob as if to light the fire, and listen closely for the familiar tic tic sound from the box. If you hear nothing, then you need to look at the igniter. There are 2 types - the commonest has a single AA battery inside. Less commonly the box is powered directly from the van 12v system. The commonest fault is of course a flat battery. Replace the battery and the box should start ticking again and the fire should light.

The fun starts if you replace the battery and the box doesn't tic. There are usually three possible causes for this. The first is that the box is broken and needs replacing. The second is that the spark wire that leads from the back of the box and into the depths of the fire to the burner has worn out somewhere and the spark is escaping to ground before it reaches the burner. The third is that the other two small wires leading to the box - the switching wires - have come loose or are otherwise broken. They come from the bottom of the control knob shaft. When you turn the knob, the circuit is completed and the box should tic.

On igniters that are powered by the van 12v circuit there will be extra wires for this. In this case you must check that the igniter is receiving 12v - the only way to do this properly is with a test meter.

On a battery powered igniter (with a new battery!) you need to check is the unit generating a spark. Unplug the spark wire from the back of the unit and operate the control - you should hear a tic tic. If not, you need to test the switching circuit. Note where the two wires come from the control knob items 27/28 on the diagram, remove the wires from the back of the igniter unit, exposing the pins, and then short out those two pins with the tip of a screwdriver - at 28. If you get a tic, then you have proved that there is a fault in the switching circuit. Look for a break in the wires. Check the wires where they join the bottom of the control knob shaft  - I have never known one to fail here, but you never know.

You need to definitely prove if the ignition unit is generating a spark tic. If it is not, then you need a new ignition unit.

If after changing the battery and operating the switch you are definitely generating a tic, but the fire is not lighting, then the most likely problem is the spark wire that goes from the igniter to the burner - item 42 to 41. After many years this wire gets old and the insulation can break down, and the spark can escape to chassis in many places. Sometimes if you listen very closely you can hear a very weak tic tic but the fire will not light. This is a good clue that the spark lead is broken or worn - it is shorting out before it reaches the burner. But it is important that you prove which is faulty - the ignition unit, or the spark lead - because changing the ignition unit is easy, but will be no good if the spark lead is faulty. Changing the spark lead is more complicated, so you must be sure that is the problem.

Changing the spark lead is a job for an engineer or a very keen DIYer. It's not rocket science, but you are dealing with gas and fumes, so you must either be competent, or don't bother.

NOTE - the drawing below is for a double burner fire - the single burner models are the same in principle.

The sequence of events is as follows. Remove the chimney pipe - item 1. Undo the lock ring and pull the pipe away. There is a silicone O ring that seals the joint. This a safety critical component and should be replaced - order one at the same time you order a new spark lead - items 8 and 42. Disconnect the gas feed pipe - if you don't know how to do this safely and competently, then you shouldn't even be attempting the job. Then remove the screws that attach the fire base plate 12 to the wooden plinth. The whole fire should now lift up and out. You are looking for the burner box 44 that protrudes down into the open below the van - either a single or a double depending on your fire. Clip 46 releases the cover and gets you inside. Then it should be obvious where the spark electrode 41 is, and trace its feed wire 42. You should see where the problem is - quite often I have seen the wire just crumble to dust. You can make your own DIY wire if you are competent, or order one. Make sure you have a good spark before re-assembly.

​Also take a good look at the burner assembly 37 - they are not expensive and it is usually a good idea to replace the whole thing if you are ordering spares​. Have a good dust and general clean up while you are in there.

Once you get the thing in bits, it's all reasonably logical. The awkward and dangerous bits are the chimney joint and the gas connection. The silicon O ring is essential to be properly placed - it stops fumes from escaping the joint and into the van. And as already stated, the gas connection is an obvious point of danger if not done properly. Do not undo and redo gas pipes unless you have learnt the proper protocols.

Solar update - big 300w panels ...

The new(ish) big panels of 300w+ - there are several available from Bimble at great prices - offer serious power for full timers and heavy users. The 30amp Tracer MPPT from Bimble is an excellent controller.

I replaced 3 120w older panels with a single 320w big panel that covers the whole of the front section of my roof on my classic S700 and the results have been fantastic. 22 amps has been the max so far in what has been an average summer in a northern latitude. But what has impressed me the most is that recent panels have a much better low light performance. I have been seeing 10 amps under cloud! I also recently installed a 320w panel on another guys 700 and that has also been a success.

But you need a big battery to store all that power, and you need to need to use it, otherwise it's overkill. With everything on - computers and TVs - all day and evening, we consume about 10amps/hour. On a bright day, even in autumn, a 300w panel will cope with that nicely. I would suggest that 200 to 400ah battery capacity is about right. I use the Odyssey PC1800 which is brilliant.

With Bimble selling 300w panels around £140 and the controller costing around £140, plus cable and bits, a high power solar system has never been cheaper - as long as you have the batteries to store it. I estimate our off grid time is about double what it was last year, with the added bonus of more power available in spring and autumn when the days are shorter.

The 3 and a half commonest Mercedes problems that can ruin your holiday.

Our beloved Mercs - the 309/310 and 409/410 pre 95 T1 Transporter chassis - are world renowned for being bombproof and good for a million. But they are not 100% perfect, neither are they maintenance free.

Over the last 17 years from my own experiences and being an active member on forums and Facebook groups, I have come to a conclusion that there are three and a half common problems that have the potential to bring a trip, or worse, a holiday, to a miserable stop. The first three are the cooling system, the gear selectors and the fuel delivery system ... and the half is the brakes - it's only half a problem with the brakes because usually they don't actually take you off the road, they just give you a fright!

All of these have been covered elsewhere in this blog, the purpose of this article is just to give a heads up to new and existing owners in case it ever happens to you.

Cooling system. 

All our vans are now over 20 years old and are usually still on their original radiators and fans. The radiators get clogged up inside and out and their efficiency reduces over the years, and the visco coupled fan gets tired and doesn't cut in when it should. Because we live in a cool country with not many mountains, you usually don't get to find out you have a problem until you are climbing up some Alpine pass in the middle of summer. Keep an eye on the temperature gauge. It it creeps up towards the red on a long hill, this is a sign your cooling system isn't 100%. A quick fix is to have all the accumulated crud blown out of the rad with a high pressure airline. This will often alleviate the problem - temporarily. Ultimately a new radiator and/or a new visco coupling mechanism may be needed to get the van back to normal performance. A system flush and fluid replacement can also work wonders. DO NOT run a Merc engine into the red or boil it over - you will crack the head and worse. The temp gauge is usually accurate - It will run to just under the red zone, but don't go there if you can possibly avoid it. Your radiator cap is also likely to be original, so if you have any cooling work done, always have a new rad cap and thermostat fitted. The water pump can also go on high mileage vans. Hoses rarely cause a problem, but should be checked.

Gear selectors.

Between the bottom of the gear stick and the gearbox is a system of rods and levers that select the gears. These can work loose, and bushes get worn leading to gear selection problems. It is rarely terminal - I have never known a Merc manual box to actually break - it is always the selectors. There are a couple of articles on here about it. Search for "gearbox".

Fuel system.

There is a gauze filter on the bottom of the fuel lifter in the tank, an inline filter between the tank and the main filter/pump, a breather pipe on the top of the tank, and the main fuel filter itself. All need maintenance and cleaning, and often have had no maintenance for 20 years. If the van is underpowered, especially on hills, or even just stutters and stops, then it is usually the fuel system. It is rarely the pump or injectors. This is a very common problem. Search for "fuel filter" for more info.

Brakes.

The back brakes on the Mercs do most of the heavy braking, especially on the 409/410 bigger vans. They need regular checking and maintenance, especially the "load balancing sensor". You don't know you have a problem until you have an "Italian Job" moment coming down 28 hairpins on the St Gotthard Pass and the pedal hits the floor. If the back brakes are not up to scratch then the fronts get overworked, get hot, and boil the fluid. Patience and engine braking will get you down safely and to a garage. Many of our vans are still on the original fluid. In extreme cases use the handbrake, which is mechanical not hydraulic. Again, this is a problem that usually manifests itself when you are a long way from the M6 - usually on holiday in the Alps or Pyrenees. Search for "brakes".



These blog articles are for guidance - I am not a qualified mechanic. There are a few other Merc related issues, but these are the main ones - not just in my own experience, but in reading the forums and blogs.

Other problems are squeaking fan belt tensioners, leaky vacuum pipes and the occasional broken fan belt - carry a spare (they are a pig to fit). Vans with over 200k can expect to need a new water pump eventually.

Have I missed anything? Please comment below.