Overheating after coolant flush

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M

motorhead

New Member
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78
Location
Dorset
Hi,

I had some funny noise going on and it was 50/50 whether it was the water pump or the alternator. I had a shot at the water pump since it only cost a few quid and since I had a scheduled coolant flush coming up anyway. Well, hey, it wasn't the water pump, it was the alternator that was making the noise.

But... instead of having just one problem, I now have two - the engine is overheating.

I replaced following parts: P-Gasket, Water Pump, Thermostat and also put them brass plugs on because the plastic ones were horrible.

I also rinsed the system to get the gunk out.

What was very funny that during the last refill I only managed to get 7 litres in (instead of 11.5). While refilling, I overfilled the tank because I wasn't looking as I expected to get further 4 litres in.

Took it for a test drive around the block and within 5 minutes it had already reached the optimum working temperature. Normally takes me at least 10 - 15 minutes to get there. I stopped, got some air out through the plug, opened the tank, got a pint of hot liquid all over myself. Drove on for another couple of minutes and the engine was properly overheated after that. By the way, there is no obvious leak; and the car has never had overheating issues before.

So, what is it?
1. Simply overfilled?
2. I got 4 litres of air somewhere in the system?
3. Cockroach or mouse or another type of pipe blockage?
4. Crappy thermostat (got it from ebay from a well-loved and respected power-seller)?
5. [fill the correct answer here :) ]

I hope you can help with some advice!
 
did you fill it through the tank or through the rad first. ? are you sure the rad is in full working order ? fill system by the rad... you said the engine was very hot, was the rad hot......
 
Last edited:
@1spin
Rad first, then put the plug on, filled through the thermostat, put the plug on, then filled the tank.

I couldn't possibly have filled it through rad alone because it came to the brim after just a couple of litres.

I have no reason to think that the rad is not full working order. It's always worked well.

@dellboy1959
Considering I don't understand the question, I might have done something wrong... :(
 
The heater matrix is part of the cooling system so if you do a drain/refill the heater Must be in the max open position (hot) in order to allow coolant into it.
If you don't do this you end up with a massive air lock.
 
Thanks guys!

@jamesmartin
How does it escape then?

@1spin
Oh, ok! Top of the rad was nicely warm while the bottom was cold-ish.

@dellboy1959
Great! I completely forgot about the core :( No, the heater control was on cold.
So, what's the best way out of this mess?
 
out of the cap ,i allways overfill it finds its own level okay ,rad sounds poor as should be hot allover if engines very hot,just fill with heater on hottest setting run engine and fan check air starts to warm ,top up tank
 
rebleed, heater controls max and hot. double check rad....:) sometimes heater matrix get blocked also, all depends how much crap was in the system... sometimes a flush can do more harm than good , moves all the gunk around ... prob the rad is blocked now also....
 
Last edited:
dellboy1959 said:
The heater matrix is part of the cooling system so if you do a drain/refill the heater Must be in the max open position (hot) in order to allow coolant into it.
If you don't do this you end up with a massive air lock.
Click to expand...


Cobblers.... the 300tdi has an air blending heater system, there is no control in the flow of coolent through it, it's hot all the time.
 
The best way to do it if it's being a total bitch is to,
1:leave the rad cap off after filling
2open the heater valve to full
3:let the engine warm up

After this the coolant may overflow from the rad but don't worry about it as this is just air trying to find it's way out.
Once it settles down give the top hose a couple of squeezes to make sure most of the air is expelled (watch out for the fan blades).Switch the engine off then let it cool off for about ten mins then check levels again,top up if necessary then fit the rad cap,run round the block keeping an eye on temp but this should of sorted it:)
 
dellboy1959 said:
The best way to do it if it's being a total bitch is to,
1:leave the rad cap off after filling
2open the heater valve to full
3:let the engine warm up

After this the coolant may overflow from the rad but don't worry about it as this is just air trying to find it's way out.
Once it settles down give the top hose a couple of squeezes to make sure most of the air is expelled (watch out for the fan blades).Switch the engine off then let it cool off for about ten mins then check levels again,top up if necessary then fit the rad cap,run round the block keeping an eye on temp but this should of sorted it:)
Click to expand...

nicely put.:)
 
discool said:
Cobblers.... the 300tdi has an air blending heater system, there is no control in the flow of coolent through it, it's hot all the time.
Click to expand...
Ok I'm not averse to different opinions but "air blending system" WTF is that,Why on earth would you want the heater matrix permanently hot:eek:
 
dellboy1959 said:
Ok I'm not averse to different opinions but "air blending system" WTF is that,Why on earth would you want the heater matrix permanently hot:eek:
Click to expand...
there no tap or valve for heater matrix, coolant just flows through it all the time ,running fan lets you know coolant has circulated through it
 
jamesmartin said:
there no tap or valve for heater matrix, coolant just flows through it all the time ,running fan lets you know coolant has circulated through it
Click to expand...
That still doesn't explain why the matrix is permanently hot and how the fan can possibly know there is air free coolant running through it?.
 
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