Overheating

[Deleted member 967]

I have the S700 Hymer on the Mercedes 410D 1992 chassis. It is overheating when pulling up hills.

I was using about a litre of water every time I checked the radiator.

I had it in for a service this week and the radiator has been drained and flushed. It was then pressure tested and a small weep of coolant was coming out of the bottom hose. The hoses have been taken off and cleaned and retightened. The system was retested and no leaks.

Yesterday I went for a test run and the temp gauge still rose to almost the top of the gauge on steep long climbs.

I did notice the fan was not cutting in as it used to do. Much shorter run only when the temperature was well into the top segment of the gauge. It used to cut in at a lot lower temperature.

The fan is a viscous fan coupled to the fan belt and running continuously. However on reading the handbook it has a clutch system filled with silicone operated by a bi-metal strip.

When the engine is cold the clutch is disengaged and spins at about 1000rpm. When the engine reaches 85c the bi-metal strip expands and the clutch engages and the fan now runs at same speed as the engine.

At 21 years I wonder if this clutch is wearing out and that is the cause of the problem. It was noticeable when the fan cut in but we are now noticing that this is not so frequent as it was even earlier this year.

I have also noticed that the temperature is varying considerably. With the interior heater fan on full and the radiator fan cutting in the temperature drops very quickly from near the top of the gauge to almost bottom (below the first mark) almost to the thick cold mark.

The gauge is divided into thirds and the pointer normally stays in the lower to centre area. The only time I have noticed it going above this before was on the long slow pull over the border into Spain from France fully loaded and towing a Smart Car on a Trailer. The current problem is even when the van is solo and lighter loaded.

We have had problems a couple of times with the fan belt tensioner. We had a new one fitted in Spain last winter at a Mercedes dealership.

Has anyone any experience of problems with these fans?

 

[Byronic]

Seems like the bi metal strip has broken or corroded. There is a means of rigid fixing viscous fans. I think it's just a bolt locking hub and blade carrier. Not so efficient having the cooling fan on continuously, but better that option than never operating. My Merc. has a fixed fan as standard, the viscous was an extra, so Merc. themselves didn't think it was that negative a practice.

 

[watchthis]

Hello John.
I have just been reading about your problem and it jogged my memory
about an item I was looking at on ebay the item number is:- 261264089712. I hope the problem you have is not the same as explained in the listing of the item above but it might pay you to read it just in case. The motorhome above is based on a Merc 410 and is a RMB.
Bye for now
Freddie

 

[Byronic]

Actually I think it's metal tabs that need bending over to lock the fan, and not a bolt.

 

[Deleted member 967]

Actually I think it's metal tabs that need bending over to lock the fan, and not a bolt.

Just been onto the local Mercedes Truck Dealer. The engine is a 602.904 type. There is only 1 fan and thermostat listed for this engine.

Viscous Fan £125 + Vat (Not held in stock but obtainable by Wed/Thursday from Germany)
Thermostat £16.90 + Vat

Thanks for the heads up on a cylinder head watchthis, but this one is non turbo.

Someone else suggested fitting electric fan but the cost of a fan and then the labour fabricating brackets and shielding would probably be more than a replacement part.

 

[Byronic]

For an OEM part that price seems reasonable. I've seen the viscous replacement for mine listed at twice that. May be good idea to see if the new fan can be locked should the need arise in 20 years time!!! That overheating problem with the aftermarket turbo "upgrade" is well known usually blows going uphill in Morocco or Spain on a hot day.
When Merc. make the turbo version of any engine they don't just bolt a turbo on, even a low pressure version, there are quite a few other mods. incorporated.

 

[geebus]

I've got similar problems on my Eurocargo.

Plan to try and lock the viscous coupling - I don't know if it is the problem, but on an old BMW I had (M3, so a fair bit of heat from the engine) I spent ages trying to work out why it overheated even on short drives and it turned out to be this, though replaced it for the proper part there.

£60 for a secondhand one of £300 new for mine.

I'm also planning to stick a couple of car electric 'push fans' to the front in series as it's 24v.
Already got them, but you can get them for fairly reasonable prices, but then of course have to spend time or money getting it sorted.

 

[Deleted member 207]

I'd expect that it is the viscous coupling, probably a serious pain in the arse to changeover - radiator out and all the ancilliaries that have to go with it - change the thermostat as well. While its out make sure that it has also been externally cleaned through the fins - I'm always amazed at the amount of seeds and road crap that fills up the fins and reduces cooling substantially.

The power that a fixed fan takes from the engine is quite substantial.

An electric fan is easy enough to fit IF there is enough room for it, on the standard 410D T1 there is not enough room for one without removing the viscous fan.

Removing the viscous fan is best left to a Merc truck dealer as there is a special tool required to get the bugger off.