Thermostat Problem?

television

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Coolant circuit, function
The coolant in the cooling system is brought into circulation by the When the coolant thermostat is in its closed state, the coolant
coolant pump. To allow the coolant to heat up more quickly in the flows to the coolant pump again and rejoins the circuit.
post-start phase, the coolant pump can be switched off by means When the operating temperature of the engine is reached, the
of the coolant pump switchover valve (Y133). The coolant pump coolant thermostat opens to switch in the radiator circuit, and the
switchover valve is actuated by the CDI control unit (N3/9). radiator then becomes part of the coolant circuit.
The coolant pump pumps the coolant into the crankcase via 2 Depending on the position of the coolant thermostat, more or less
independent coolant inlets. coolant now flows through the radiator or directly to the coolant
Part of the coolant is fed simultaneously to the cylinder head, to pump. The temperature of the coolant in the coolant circuit is
the oil-water heat exchanger and to the exhaust gas recirculation regulated in this way. The coolant thermostat is controlled by the
actuator (Y27/9), the bypass housing and the exhaust gas CDI control unit via the coolant thermostat heating element.
recirculation cooler via the chain case housing. The temperature-dependent coolant level is adjusted by means of
The coolant flow of the oil-water heat exchanger is controlled by a the filling line between the coolant expansion reservoir and the
thermocouple depending on the engine oil temperature. radiator.
Part of the coolant is then fed via a coolant collector to the heat The cooling system is ventilated via a vent line between the
exchanger for the vehicle heating in the vehicle interior and the coolant expansion reservoir and the coolant collector.
other part to the coolant thermostat housing.
----------------------------------------------------------------------------------------- -----------------------------------------------------------------------------------------
 - The limits stored in the CDI control unit for the intake air and
The coolant pump is switched off for a cold start for a maximum of coolant temperature as well as for the injected total fuel
500 s if the following conditions are fulfilled: quantities are still not reached.
- The engine speed or injection quantity has not exceeded its
established limit value.
- No "heating" was requested by the automatic air conditioning
control and operating unit (N22/7).
 
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survey

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Interesting you say this. I thought there couldn't be a connection but I have noticed that if I turn off the A/C completely the car goes quickly goes straight to 92 without the hunting around 75-80?

I did a 90 mile round trip today and it took 25 mins and 20 miles (primarily motorway) before it settled at 92 after the usual hunting around 75-80 but then it stuck there all day without moving a micron.

Simon

That is exactly how my car behaves and also my previous cdi car!

I still await a response from MB Technical!
 

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So just to re-cap: car behaves normally?
 
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survey

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Just received areply from MB technical (actaully only after I phoned them to see why I hadn't had a response).
They respond saying that all MB's should run at a temperature between 80 and 100. Any temp within that range is OK. They made no comment about the 'hunting' that I have noted between 75 and 80 just saying that all depends upon the way the car is driven. So the MB franchise that I spoke to initially that informed me all MB's should run at 82 degrees is incorrect.
 

television

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Just received areply from MB technical (actaully only after I phoned them to see why I hadn't had a response).
They respond saying that all MB's should run at a temperature between 80 and 100. Any temp within that range is OK. They made no comment about the 'hunting' that I have noted between 75 and 80 just saying that all depends upon the way the car is driven. So the MB franchise that I spoke to initially that informed me all MB's should run at 82 degrees is incorrect.

If you care to read the info that I put up it explains this
 
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Just heard from my MB dealer and I have relayed to him the info from MB Technical. Despite this, he still requests that I take my car in on Monday for a diagnostic check etc. I will post the outcome afterwards.
 
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Car went for diagnotics and I was informed all was fine! So having been told by my dealer that 82 degrees is the temperature the cars should run at, my continues to show 90 and the dealer now says it is fine! MB technical previoulsy said anything betwen 80-100 is fine.
Whilts at the dealer they said the car had an engine & gearbox update. It will be interesting to see if after this the temperature gauge still hunts between 80 and 75 prior to going up to 90.
 

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Installing Engine Pre-Heater

I have done another search and I see that your cooling circuit is a 2 stage one with a heater in the system

Not one word anywhere on the temp on the 651 lump

I have printed the circuit off if you would like to read it I can send it



Hi

I just joined, and I saw this post.

I'm trying to install an Engine Pre-Heater of the 'in-hose' variety.

My workshop have tried three times, and each time the heating-element burned out (apparently no circulation, and the liquid boils off)

The heater (Defa type 702 or 708) has no thermostat.

Could you be so kind (or somebody else) explain which hose to cut, to install the electric heater correctly (I plan to buy one with a circulation-pump)?

Could you also confirm that the heat-exchanger (i.e. the heater inside the car) circuit is "open" when the engine is not running?
 

television

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The original heater was a diesel heater fitted under the right front wing.

The heater matrix cannot be guaranteed to be full when off. Block heater were used when I lived in Sweden, the bottom hose is always full.
 

TomZie

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The original heater was a diesel heater fitted under the right front wing.

The heater matrix cannot be guaranteed to be full when off. Block heater were used when I lived in Sweden, the bottom hose is always full.

Hi

I know about the Webasto Diesel-powered Pre-Heater, but that is mounted in a completely different manner.

And, I'm not talking of a "Comfort Heater", i.e. a system which heats the interior of the car.

I'm talking about a Engine Pre-Heater, i.e. a heater, powered by 240VAC, which heats the engine before starting in cold weather.

Such as the Block-Heater (in the old days mounted instead of one of the "Frost-Plugs", later mounter in a threaded connection directly on the engine block) except that there is no place to fit a Block-Heater on the OM651 engine.

Therefore I need to fit a "Hose-Heater".

I just need to understand if the "Secondary Cooling Circuit" (or "Small Circuit" which it is sometimes called), where the water is circulated through the Heater Matrix and the engine block, is "open" when the engine is not running.

Or, if there is any sort of valve in this circuit, which is normally closed and only opened when the engine is running?
 
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television

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No, that heater loop is all time active, no valves. It depends on where the heater circulation pump is fitted to guarantee that there is water in the system all the time, if it is low down then yes, water all the time. if mounted high up, then you cannot be sure that there is water all the time. the heater water pipes leave the engine block at the rear, this goes through the firewall into the cabin to the heater matrix, then back to the cars cooling system radiator etc.
 
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