Help ! 300tdi Gushing Coolant ..

[dogdog1]

Hi All , Fitted the new radiator , hoses , and thermostat to my project 300tdi 110 today . Filled with coolant via the expansion bottle to correct level with bleed bungs out , squeezed top hose til no more bubbles and replaced bung , topped up thermostat housing and replaced bung . Then I fired it up and thought it might be an idea to leave the bottle cap off to aid clearing the air out of the system , but within a few minutes the coolant came right to the top of the bottle , I replaced the cap and switched off the engine , a minute later the coolant was forcing its way out of the bottle and when I released the cap about a liter of coolant gushed out . Anyone got any ideas on this ?

[PAT303]

Remove the heater matrix outlet hose and reconnect when coolant flows out of it when filling the header tank,also disconnect the thermostat bypass hose and check to see if the housing is full.My guess is you have air in the system still. Pat

[BathurstTom]

Take the tank cap and the two bungs out - 1 in the radiator and 1 in the thermostat housing. Fill the radiator via the radiator bung hole until it is full and then replace that bung. Slowly fill the thermostat housing and replace the bung. This will overfill the expansion tank. Remove excess and replace cap. Run up to temp, allow to cool a little, remove cap and check level. Top up if necessary.


I have just replaced the head and this method works well (not the first time I have used it). I did as above on Tuesday afternoon and it is all good.

Tom.

P.S. ensure heater is on to circulate it there too!

[dogdog1]

Take the tank cap and the two bungs out - 1 in the radiator and 1 in the thermostat housing. Fill the radiator via the radiator bung hole until it is full and then replace that bung. Slowly fill the thermostat housing and replace the bung. This will overfill the expansion tank. Remove excess and replace cap. Run up to temp, allow to cool a little, remove cap and check level. Top up if necessary.


I have just replaced the head and this method works well (not the first time I have used it). I did as above on Tuesday afternoon and it is all good.

Tom.

P.S. ensure heater is on to circulate it there too!

Tried to follow this advice today but the engine will not warm up at idle , could place hand on side of cylinder head for a few seconds and all hoses cold but pressurized . I'll remove the fan tomorrow , if it still won't warm up I'll have to revisit this when I have it otherwise roadworthy and can take it for a run .

[jboot51]

Sounds like you had an air lock.
The 300 tdi takes a good 15 minutes or more to heat up at a fast idle without any load.

[BathurstTom]

As said above, it takes a while to warm up. It helps if you put a/c on and cover the grill for a while so it restricts the air flow. And don't forget to move your heater temp control to hot so that you get full circulation.

I just re-read your post, you should not have all hoses pressurised if it is still cold - do you have a correctly functioning thermostat?
Tom.

[schuy1]

There is no tap in the heater circuit on a 300TDi or a TD5 either for that matter. They are a contin flow only the airflap diverts airflow through the matrix or bypasses it for heating or cooling. Removing the top heater hose while filling can help, although I have never needed to. Just follow the "coke bottle" fill method and ya cant go wrong!
Cheers Scott

[loanrangie]

Pressurised hoses = gasket and or head knackered.

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[dogdog1]

Hi, got it up to temperature on the gauge today minus the fan , looked like it would have continued to rise too . All hoses were cold but pressurised , radiator and air from heater also cold . The thermo is new . Loosened the tank cap very carefully and avoided the splurge but as I did so I could hear and feel a right bubbling in the tank as the pressure escaped . It had filled itself up again of course . The coolant in the rad had dropped by a couple of inches and I could not see any in the thermo housing . Ideas ?

[loanrangie]

Do you know the history of the motor ,gasket and head ?
If its the original head my bet is on it being cracked.

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[dogdog1]

Do you know the history of the motor ,gasket and head ?
If its the original head my bet is on it being cracked.

Sent from my GT-I9300 using AULRO mobile app

No history at all , I rescued this from a yard where it had been lying for some years . Two core plugs were missing from the block and one from the side of the head , there might be a clue there . With the plugs replaced the engine started easily and drove very well on the 4 miles home , although the temp gauge was starting to climb by the time I got there . What surprised me today was the way the engine could warm up but the heat didn't travel into any of the hoses . Failing any other solution , I'll have a sniff test done .

[BathurstTom]

As far as I know, if the block/head are warming up and the water is topped up, the only way the hoses can still be cold is either a defective thermostat or pump.

Tom.

P.S you said you disconnected the fan - you didn't take the belt off did you?

Tom.

[dogdog1]

As far as I know, if the block/head are warming up and the water is topped up, the only way the hoses can still be cold is either a defective thermostat or pump.

Tom.

P.S you said you disconnected the fan - you didn't take the belt off did you?

Tom.

No , didn't take the belt off , just the fan ! Just wondering though , if the pump isn't working how is the coolant getting from the engine and rad to the header tank ? Remember it it will start to do this near enough straight away .

[BathurstTom]

Did the motor get hot enough for the thermostat to open? it has to get to 88 degrees (I think) for a standard thermostat.


Tom.

[dogdog1]

Did the motor get hot enough for the thermostat to open? it has to get to 88 degrees (I think) for a standard thermostat.


Tom.

I let it run til gauge went just a shade past half way . Don't know exact temp though . New thermo is in correctly . It's behaving exactly as it did when I drove it home with the old hoses thermo and rad .

[dogdog1]

I fixed it ! ... briefly . Now it's only half fixed . Yesterday I ran it up to temperature , with the tank still overfilled , and the rad and thermostat housing still low and with bungs removed . Keeping an eye on the gauge I noticed it drop back a little to the cool side , at that point I carefully added coolant to the thermostat housing , when it stopped bubbling I replaced the bung then topped up the rad and did some hose squeezing and replaced the bung . Lo and behold the heat was traveling all round now , temp holding steady , heater working well and no hard hoses . Came back later and gingerly undone tank cap , just a bit of hissing but no spillage . The coolant had dropped from full to about an inch and a half less . Came back to it today , fished out the excess coolant and ran it up to temp , but on this occasion there was no drop in temperature and the heater and it's hoses and rad remained cold and only the hoses from the thermo housing to water pump and from behind the pump warmed up . On the plus side the tank level dropped slightly and hoses aren't going hard and coolant has not risen . So it's looking very much like a circulation problem . Could a new thermostat really be faulty ?

[jboot51]

The thermostat could be the culprit.
Make sure it is fitted with the little hole at the 12.00
position. This lets the air purge.
The other culprit is the plastic 3 way connector and 1/4 hoses that connect the rad/thermostat/expansion tank. Make sure this has flow in all directions and is not blocked.
Even with the thermostat closed there is flow through these hoses.