Ron Bentham's Funky Mercedes Hymer S700 Motorhome blog: 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.