Over heating problem

[Mr_J_P]

Hello All,

I was wondering if you can help me,

The engine keeps over heating very quickly, i'm not sure of the cause and what the best solution would be.

Does any one have any suggestions?

[heinkeljb]

Re: Over heating problem

check for a water leak? Do you have to top up the radiator often?

John

[Mad smart person]

Re: Over heating problem

Greetings, engines usually over heat because of lack of cooling. The thermostat, remains closed untill the water (coolant fluid, a mixture of antifreeze and water) gets hot enough to cause the thermostat to open, then the water pump pumps the fluid round the system to help cool it. If the thermostat does not open the engine gets hot VERY quickly. Other causes of over heating, water pump impeller failure, air in the system, it usually gathers at the high parts of the engine and this is where the heat is, air is NOT a good conductor of heat, water, sort of is. Other causes of blockages are bent or squished pipes/plumbing - either rubber or metal. Blocked radiator, lack of water in the coolant system. It is a closed system and there are precautions to be taken when opening the system up, ie, don't take the cap off the resouvour when the water is hot, the temp can be approaching 110 Deg C. Also, antifreeze is not good for your health, either in liquid or gas form, you don't want to drink it or inhale it, it's not too good on your skin either, hot or cold. FQ101 has a procedure on how to service the coolant system, once you've found what the problem is. Cheers, Ian.

[tolsen]

Re: Over heating problem

Head gasket will blow if you don't get the overheating problem fixed.
1) Check coolant level.
2) Bleed coolant system.
3) Top up coolant system.
4) Monitor coolant level. There is obviously a leak somewhere if level keeps dropping.
You can carry out a block test to confirm whether head gasket has blown. Evidence of oil in coolant or white emulsion forming in rocker cover and under oil filler cap means there is a head gasket problem.

[Mr_J_P]

Re: Over heating problem

Thanks for your replies, I really appreciate it I hope its nothing serious.

[Mr_J_P]

Re: Over heating problem

two questions,

how do I check if the pump or thermostat is not working?
And how would I replace them, I have these parts already.

[tolsen]

Re: Over heating problem

two questions,

how do I check if the pump or thermostat is not working?
And how would I replace them, I have these parts already.

Forget about replacing pump unless its bearing has worn out and pump is leaking.
Checking thermostat is easy. First bleed cooling system by lifting coolant temperature sensor whilst expansion bottle cap is off. Sensor is held in place with a metal clip. Tie a rope or something to the clip so you won't loose it. Mine has a tie wrap permanently attached - something you may consider when refitting clip.
Run engine and keep feeling on the large hose that goes from thermostat to radiator. The smaller hose goes to heater matrix. The large hose will suddenly get hot when thermostat element opens. Thermostat element is fubarred if engine gets too hot and this large hose never gets hot.
There is a good guide on FQ101 explaining how to renew thermostat.
All hose clamps fitted are the Clic E or R type. You need a special tool to reuse these.


Clic hose clamps are easy to open without any special tool. Just pry open the catch using a suitably sized flat bladed screwdriver from the side.

[Mr_J_P]

Re: Over heating problem

Thanks,

I've read elsewhere that if the heaters are blowing out hot air then the thermostat is ok?

Is this true? because my heaters blow hot air completely fine.

Or should I still check?

[Mr_J_P]

Re: Over heating problem

i've also heard that the problem could be the fan behind the radiator?

[tolsen]

Re: Over heating problem


Above diagram shows coolant system for the 450. I assume the Roadster is similar. Oil cooler is not shown. Applies to the Cdi, Roadster and all Brabus engines. Restrictor plug is built into thermostat housing fitted in the petrol engines but not into thermostat housing for the Cdi.

Coolant is always being circulated through engine, through bypass (the short pipe from thermostat housing to pump) and through heater matrix and expansion tank. This means heater matrix gets hot regardless whether thermostat is open or closed.
Radiator cooling fan is switched on by engine ECU when coolant temperature sensed by temperatur sensor at top of thermostat housing is above a certain level, probably just above 95 C. Thermostat should start opening at 87 C.

You get an accurate reading of engine temperature by measuring temperature in expansion tank. You should see coolant being circulated if you look down into the tank. No circulation means there is air in the system causing an air lock. The only way to sort this out is by bleeding system.

[tolsen]

Re: Over heating problem

i've also heard that the problem could be the fan behind the radiator?

Test operation of radiator fan by simulating a fault such as open circuit in lead to coolant temperature sensor. Unplugging sensor creates an open circuit fault causing engine ECU to switch on radiator fan to protect engine from overheating.
A quick and easy test.

[Mr_J_P]

Re: Over heating problem

thanks,

is bleeding it through the temp sensor nessessary as this guide
http://www.evilution.co.uk/133

says there is a bleeding point at the front.

I have used the bleeding point at the front and quite a bit of air was released and a little bit of fluid.

[Mr_J_P]

Re: Over heating problem

Test operation of radiator fan by simulating a fault such as open circuit in lead to coolant temperature sensor. Unplugging sensor creates an open circuit fault causing engine ECU to switch on radiator fan to protect engine from overheating.
A quick and easy test.

Will this test make any fault lights come on?

[tolsen]

Re: Over heating problem

The proper way to bleed is by lifting temperature sensor. The other mickey mouse method may work if you can position your car front facing up a very steep hill. I have however not bothered trying that method as lifting temperature sensor works each time.

[tolsen]

Re: Over heating problem

Will this test make any fault lights come on?

No warning lights appear on mine but the ECU will most likely record a historical DTC if you leave plug disconnected for a sufficiently long time.