Monday 22 June 2015

Mercedes Engine Cooling Fan issues ......

This is a query about cooling on the D310 Merc engine. The electric fan on our 1994 S555 cuts in regularly on motorway journeys at 50-55 mph even though the external temperature is well under 20C and the engine temp gauge is only around or maybe just above the halfway mark. Is this normal or is there some way I can adjust the thermostat on the fan? I wouldn't mind except that it's really noisy. Thanks for any advice.
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  • 3 people like this.
  • Christian Skeels Is it an OM602 engine? As far as I am aware, the original fan was some sort of viscous coupling that engaged when a set temperature was exceeded. That's certainly what I have on my S550. These were problematic though and it's quite possible it has been replaced with an electric fan during the van's life. I am not aware of any electric fans being fitted as standard pre-1995. Happy to be corrected though!
  • Richard Benson Should be a 602 engine Christian, and unless modded it would have a viscous coupling. Mine only comes on on long climbs in the mountains when it's rate ot
  • Ron Bentham Unless you can see what is obviously an extra electric fan bolted on the front of your radiator - then you don't have one! What you do have as CS says, is the original Merc viscous coupled fan - it just sounds like an electric fan! I am very familiar with this problem - it drove me nuts for years on my old S700, which is basically the same engine. The fan looks like it is driven by the fan belt, and it is, but if you look closely you will see that the aluminium centre of the fan has what looks like cooling vanes. Inside there is a clutch which is operated by a fluid. When the fluid gets hot, it expands, engages the clutch, and power from the belt is transmitted to the fan blades, which speeds sucks more air through the rad, and cools the water, which cools the engine, which then runs cooler, so the air flowing through the rad gets cooler, which disengages the clutch in the fan..... And the noise you hear like an aircraft engine is the noise the fan makes when it is under full load. And unfortunately the VCF is a bit of a blunt instrument, and with no way to adjust it - so over it's life the point at which it cuts in and out changes slightly, and if you are unlucky, as you are and I was - it can cut in and out at cruising speed.

    You will notice the temp gauge needle rising and falling slightly as the cycle happens.
    16 June at 19:50 · Edited · Like · 3
  • Yes, same on my 1985 OM617. In it comes, with a big whine. Mine seems to run a bit hot, so it kicks in fairly frequently. Anyone here done a flush of their water system, to save me hunting down the best method?
  • Ron Bentham So what you end up with is a positive feedback loop - the fan cuts in, the temp drops, the fan cuts out, rinse and repeat.

    The bad news is you can do nothing about it. There is nothing to adjust. The options are either to completely replace the fan assembly, which is what I did, at a cost of around £400, or the other option is to add an electric fan on the front of the radiator, with an adjustable thermocouple which senses the engine coolant temperature, and powers the fan accordingly. This should have the effect off keeping the engine temp down below the threshold at which the original fan does it's annoying in and out shake it all about routine. It would be even better to have the thermocouple control in the cab, so you can adjust it as you go. This is a reasonable DIY project if you fancy it - the fans are on Ebay for less than £50.....and the other bits are cheap - you could do it in a day if you know what you are doing.

    You may ask why did the otherwise infallible Mercedes design team do it this way in the first place - the answer is that when the fan is operating, not only is it noisy, but it takes quite a lot engine horsepower - which you may have noticed as a drop off in speed when the fan cuts in, especially on those long motorway hills - often necessitating a change down in gear. So they tried to design a system that keeps maximum horsepower to the wheels, and only to the fan when necessary. And it does work, usually you don't even notice. But unfortunately in this case the fan system hasn't aged as gracefully as the rest of the engine. The problem is even more pronounced sometimes with those vans that have been turbo'd and intercooled, as the intercooler sits in front of the main radiator and upsets the airflow even more. Basically it would have been better if merc had fitted an electric fan as standard.

    Hope this helps.
    16 June at 19:51 · Edited · Like · 2
  • Nigel Pigott Fantastically helpful response, as ever – many thanks Ron and others. The electric fan solution seems very attractive. I'm guessing something like this: http://ebay.eu/1JTfLBH. There seems to be a mounting kit with it so I just need to find a suitable vacant slot on the fuseboard to wire it in (there seem to be lots) and then I might be able to listen to Radio 4 without turning the volume up to 11.



    14" AeroLine Universal Electric Radiator 12v Cooling...
  • Ron Bentham Yes thats similar to what I saw - just do a bit more research as to how the fan cut-in is actually controlled.

  • Ron Bentham That is exacly what you want - cheers xxx - those instructions are clear and concise. In my case it will be more complicated because when the intercooler is fitted, space is tight. I am hoping I can squeeze an electric fan in between the two. But first I will see how the newVCF I am having in the new S700 fares next week.
  • Nigel Pigott Thanks xxx and Ron. Almost ready to put in my order but having measured up I think I will need to go for a 12" fan as there is a fixing bar across the front of the radiator that would prevent a larger one being mounted flush. EBay has separate thermostat kits with relay and controller for under £10.
  • Ron Bentham Please post back when you have a result!
  • Gary Garage Johnstone Can I chip in on this thread.... I used to fit these type fans to TVR's and the way to control these units was to use a thermo sensor that was slotted into the top radiator hose (being the hottest point) the sensor was connected to a long fat flexi tube which then was attached to an adjustable temperature control that needed no physical wiring apart the fan as it activated the fan when it felt the need at the temperature set..http://www.ebay.com/.../Universal-12V-0-120.../171787644274



    Speedmaster adjustable fan wiring kits are designed to...
  • Nigel Pigott Thanks Gary. I was looking at this one as I don't really want to pay $23 postage: http://pages.ebay.com/link/?nav=item.view&alt=web... . Looks similar? Off to Pembrokeshire for a week or so next week so probably won't be able to do anything until we get back.
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5 comments:

  1. Rory3 April 2018 at 16:58

    Did any1 fit an electric cooling fan in the end? About to turbo charge my 1992 s660 Hymer with merc OM602 2.9 engine and want ensure I have adequate cooling. Any links to the final selection and pics of installation would be appreciated.

    ReplyDelete
    Replies
    1. funkyronster5 April 2018 at 01:57

      I don't think so. The problem with fitting an electric fan to a merc is that there is very little room between the engine and the fan, and removing the existing fan would be a major job. The only place for an electric fan would be on the front. If you are turbo charging a van, you should also be intercooling it, and this is where the intercooler is usually fitted. On my van, turbo charged by TB in Lancaster many years ago, the intercooler sits in front of the existing rad. I simply don't see the need for an electric fan in a Merc, as long as the visco fan is in good working order. The stock cooling system works very well and easily copes with the extra load of a turbo. TB chose not to make any mods to the cooling system ...

      Very interested to hear about your turbo conversion please!

      Delete
    2. Rory26 April 2018 at 16:22

      Yes, I will be intercooling aswell. At what mileage is it recommended to change the water pump? I am looking to fit a new radiator when turboed to keep cooling at optimum. I have 99% of parts for the turbo conversion plus a modified fuel pump from ‘diesel pump uk’. From my understanding TB only tweaked the stock pump. So the modified pump should help deliver some extra hp/torque. Will keep you posted.

      Delete
  2. funkyronster28 April 2018 at 08:13

    Please do! Really interested ... especially in the pump. I am planning on visiting DP. I am convinced I am not getting much performance out of mine.

    How are you fixing the turbo to the manifold? have you had a custom one made?

    ReplyDelete
  3. funkyronster28 April 2018 at 08:44

    The water pump on my last van lasted 300k km.

    ReplyDelete

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