Coolant woes

[ollieplimsoles]

I drained, descaled and attempted to refill the coolant system of my 1991 2.0 190E auto today.

I must have caused an airlock.

On refilling I can only get it to swallow approx. 5L of the necessary 8.5L of coolant, (a 50/50 mix).

The low coolant level light is illuminated.

The car runs ok though with the temp. needle staying just above the 80 mark during running. It begins to rise quite quickly though when idling in traffic etc. but this is mainly due to a separate problem - namely a failed viscous coupling as the fan just turns like a windmill all the way to 100+ and can be stopped by hand.

Any quick solutions to my perceived airlock problem?

I didn't remove radiator or engine block drain plugs - just the bottom hose of the radiator - is this what I get for trying to cut corners?

Regards,

Mark S.

 

[Frank O' Phile]

A 'technique' I have used in the past is to let the engine idle with the pressure cap off the reservoir. Eventually the air will bubble out. Can be a bit messy but has been effective on other cars I've had. Not tried it on a Merc. Yet.

 

[Dec]

As Frank, also have you turned the heater dial to the hot position to allow water to circulate through heater?
Not removing radiator or engine block drain plugs would make no difference.

Dec

 

[grober]

You should have an electromagnetic fan coupling not a viscous one. The thermal switch on the cylinder head for these sometimes fails. Worth shorting across it to see if the fan starts. Make sure you have the heater control on hot to get rid of any air in the heater matrix. You wont have drained the entire contents of the cooling system without opening the block drain. Its always a good idea to measure what you drain from a system to compare with the overall capacity. Then you know what to put back. Get your car facing up on a sharp incline such that the coolant reservoir is roughly the highest point of the cooling system. Warm the car up first with the pressure cap off and once the thermostat is open then squeeze the top and bottom hoses to displace any air blockages. Finally replace the pressure cap on the reservoir making sure its topped up to the level. When the engine cools down it should draw any coolant needed back into the system you can then top it up as necessary.

 

[Dieselman]

As gober, you haven't fully drained the system so 5 litres will be pretty well all it will take back in.
As Frank just leave it idling with the header cap off and fill as the level goes down. It could take a while to purge the air so leave it idleing.

 

[ollieplimsoles]

Thanks guys - I'll sort it out next weekend.

Interesting point on the type of fan Graeme. When discussing the fan problem elsewhere, I was told that, according to the VIN number of my car, it had a viscous coupled fan fitted.

Must double check. I presume that if it is an EM coupled fan there will be wiring to it somewhere as well as the switch connection?

Regards,

Mark S.

 

[grober]

Thanks guys - I'll sort it out next weekend.

Interesting point on the type of fan Graeme. When discussing the fan problem elsewhere, I was told that, according to the VIN number of my car, it had a viscous coupled fan fitted.

Must double check. I presume that if it is an EM coupled fan there will be wiring to it somewhere as well as the switch connection?

Regards,

Mark S.

I may be mistaken--often am. At least it should be easy to find out by inspection. The viscous coupled fan will have the familiar grey metal finned centre section whereas the magnetic coupled fan will be completely plastic with a thin black metal "drum"behind the fan with electrical connections going to it.