Oil all over the road and the engine? Don't panic until you have checked this.

Oil all over the road and the engine

It's easy to get that sinking feeling when the oil light comes on and when you look under the van there is oil everywhere.

That is exactly what happened yesterday to my brother in his S670. It's not a common thing - in all my years with the van and answering questions online and reading forums I have come across it very rarely, if at all. So when it happens you can be forgiven for fearing the worst. After all there are very few places where the oil actually has access to the outside world - and most of them horrible and expensive - head gaskets, blown engine etc ...

But as it turns out, there is one place where the oil can escape in panic inducing quantities - but is easy to fix and only costs a tenner plus labour, and you can find it and do it yourself. I am talking about the oil pressure switch. This is a small circular component with a wire attached that screws into a hole in the engine block. It is located under the inside engine cover at the lower left of the block as you face the front - see photos.

As you can see the oil gets everywhere so it can be difficult to see where it is coming from at first. In my brother's case the van was running fine and did not cough and splutter or make strange noises and no smoke from the exhaust - just the oil light came on, so he stopped immediately. After a bit of discussion we decided to wipe away as much of the oil as possible and then start the engine again for a few seconds to see if we could spot the leak. The dipstick was reading just under full, so we knew there was plenty of oil in the sump. taking off the inside cover we were greeted by what you can see in the photo - not pretty! - so we cleaned and looked here first.

Neither of us are expert mechanics, just amateurs, and neither of us actually knew the details of just how the oil pressure light is operated. I made a call to my mechanic friend Wayne in N Wales and sent him the pics on Whatsapp. Straight away he said that it would most likely to be the oil pressure switch located as in the photos. After just a few seconds of the engine running we could see it oozing out, and when we gave it a few more revs the light flickered a bit and went out and then back on again. Wayne then said as long as there was oil in the sump and showing on the dipstick then it was safe to drive a short distance. Sam was only a couple of miles from base so he limped back, ordered a new switch and fitted it the next day. It's an easy DIY job, all you need is a spanner and brother Sam had to replace the wire connector because it was seized on - been there since new over 20 odd years ago so we'll forgive it. The switch has a plastic body and this had eventually cracked with age.

Of course it goes without saying that if you are pouring out smoke and the engine sounds like a spin dryer with a brick in it then it is unlikely to be the pressure switch. You should never ever drive with the oil light on unless you are absolutely sure you know the reason, as in this case.

So if a similar thing ever happens to you, don't panic until you have checked that it's not the oil pressure switch. Panic over!

If ordering online search for "Mercedes T1 oil pressure switch", or "OM602 oil pressure switch". It was used in lots of other vehicles and there are many different oem part numbers.

Location of switch - and source of oil leak

Oil cleaned away and leak exposed after running engine for a short while

Switch taken out 

New switch ready for installation

Cleaning the Truma blown air heating fan makes a difference! And general background info on Truma heaters

On most 5 and 6 series classic Hymers, heating is provided by a Truma heater - see photo. It is usually either a Truma 3002, or a 5002. (The Hymer S700 has a 3002 in the back, near the bed and an additional Truma 2800 heater under the table in the front - this article is not about the 2800, which is a completely different beast).

The difference between the 3002 and the 5002 is that the 5002 is higher power and used in the bigger vans - in particular the S660 and S670.

These heaters work both by radiating heat from the front of the heater and by drawing air through the front of the heater by a fan mounted on the back of the heater which then pumps the heated air through a system of pipes to outlets around the van. The heater is switched on by the knob on top of the heater, and the fan is operated by a small control box marked "Truma Vent" - the location of this control varies according to the van. This control has an on off switch - which only controls the fan, and another switch which selects low or high speed. The on/off switch is three position - centre is off, up is automatic, and down is manual. There is a large rotary knob which in automatic mode controls the temperature by varying the fan speed according to the temperature, and in manual mode simply controls the speed of the fan. If the heater is switched off, then the fan simply circulates cold air, which is useful for keeping the air in the van moving around, but in practice is rarely used - it's easier to open windows. The automatic function quite often degrades with age owing to deterioration of the temperature sensor in the control box. You have to experiment to see what works best for you.

The fan does not take much electricity - about half an amp. A full battery should run the fan non-stop for at least 3 days.

(I have seen forum posts from owners asking if it ok to run the heating system all night - the answer is yes - it is designed this way! You should experiment with your system in different outside temperatures and you will soon find the settings which work best for you)

Like all things in the van, things need cleaning and servicing occasionally and the heating system is no different. The most common problem is a gradual reduction in efficiency which is caused by the blades of the fan becoming caked with years of dust and grime. It is important to remember that the air is drawn from inside the van, not outside, so all the cooking smells and particles contribute to this over the years. If you have bought an old van you have no way of knowing just how furred up your fan is - it will always work, but the system will only work at maximum efficiency if the fan is clean and shifting air at its designed capacity. 

It is also important to keep an eye on the air distribution pipes (ducts) because after many years of use and vibration, they can occasionally get damaged or disconnected at one of the many connections around the van. It pays to know where the pipes run in your particular van, and keep an eye on them. A disconnected or damaged pipe can ruin the efficiency of the whole system.

A particular characteristic of this system is that in many old Hymers when the fan is running, it can "sing" - a high pitched gentle whine. This isn't a design feature - when the fan left the factory the fan would not be singing, all you would hear is the gentle rushing of air, depending on the speed of the fan. The singing sound develops over many years and is either due to a build up of dirt on the fan, which affects the balance, or the gradual wear of the fan motor bearings. 

If the fan is noisy - ie singing - then the first thing to do is to clean it. It probably has over 20 years of dust and dirt in it. The fan is mounted on an aluminium hood (also called a cowl) that is mounted on the back of the fire. The fan is mounted on the cowl, and the pipes are connected to the fan. When switched on, the fan draws cold air through the front of the fire, over the heated body, and then pushes the hot air into the pipes and around the van.

You can use the heater in "radiator only" mode - ie with the fan switched off. This is often useful for background heating the van because it uses no battery power at all in this mode. However I have seen some vans where the fan is always forced to be on to prevent over heating - S670 for example.

To get at the fan you have to get access behind the fire. Access depends on the layout of your van. Then you should be able to see the fan. Disconnect the wires and pipes from the fan - make a note or take a photo of where everything goes - it is very simple, just 3 or 4 screws. Then remove the fan - it is attached by just 3 screws. The fan may have a plastic cover which is easily removed. You will then be able to see inside the fan and you will see that the wheel is caked with a lot of dirt and dust. Clean everything carefully - compressed air helps. Then re-assemble. The only tools you need are screwdrivers and common sense.

This does not guarantee that the singing noise will stop - every fan is different - but it should reduce the noise, and it will certainly improve the airflow. What used to be just a gentle trickle of warm air from the vents might now be a proper flow - I have been amazed at the improvement in some of the heaters I have worked on. 

It is a characteristic of Truma fans that after many years some of them sing - some more badly than others! If you do not like the sound of your fan after cleaning, then the only option is to change it. New fans are still around if you look hard enough, and I have read online that some owners have replaced the motor only.

While researching this article I found this web page which is very useful for manuals and schematics. There is also a load of info on Trumas if you Google - particularly on German forums - use Google translate.

https://dealernew.truma.com/_anweisungen/Truma_Katalog/2%20gb/s_heizungen_gb/trumatic_s_ues_gb.html

Other Truma problems ...

Ignition. I covered ignition problems in this blog - 

https://hymers700.blogspot.com/2017/01/truma-3002-fire-wont-light.html

I have also been asked can you run the fire when driving. The answer is no because airflow down the chimney will blow out the fire. However many owners forget to switch off the fire and drive away ... the fire will blow out and the safety interlock will kick in. At the end of your journey when the van is quiet somebody will say "what's that ticking noise?" - it is the ignition circuit. Many owners have a pre-drive checklist and switching off the fire should be on it!

Most other problems are not DIY jobs because they mean disconnecting the gas supply, the flue and removing the heater body. Jobs that needs this include replacing the ignition HT lead - covered in the other article, or replacing the burner assembly. The control valve at the bottom of the long rod from the control knob can also be replaced. These jobs should not be attempted unless you are fully confident and are absolutely comfortable working with gas and flues and can be fully confident that you have reconnected gas and tested for leaks. Gas engineers are certified for a reason - gas can kill you, as can carbon monoxide from an improperly connected flue.

However I must stress that the main subject of this article, cleaning the fan, has nothing to do with gas and can be done by most DIY persons. Or if you are not confident, a dealer (who knows his stuff!) should take a couple of hours to clean a fan, depending on how easy it is to get at the back of the fire. You could ask for this to be done when you are having other work done.

Front - you don't usually have to take off the front to service the fan

Behind the Truma. Every van is different - this one is easy access! You can see the aluminium hood and the fan is inside the cream plastic cover which is attached to the hood with 3 screws. Disconnect the pipes from the fan, and also the wires.

Also in this photo you can see the hot air pipes (also called ducts) leading off into the van - trace yours and check for damage and disconnections. If there are any then the whole system will not be at the right pressure and not efficient. You should have even heat coming out of all the round vents - if you have one or more vents noticeably cooler than the others, then that is a sure sign of a problem.

These are the blades you must clean. I have seen them much worse than this - so dirty that hardly any air flows at all!

These photos were taken from a German forum and I acknowledge this.

There are more photos and info on this German forum

https://www.wohnmobilforum.de/w-t64969.html