Coolant Level and Light

[scotinoz]

Looking for some help, driving yesterday and after about 30 mins the coolant light comes on and I notice the temp dial goes from 90 to 120 and back again in about 20 secs. Does this a couple times so I pull over, expansion tank level looks low and water has obviously sprayed somewhere up high as pipes around tank are wet. Did it again today although the tank level does not look as low? No water in oil or oil in water. Could it be a defective cap releasing pressure causing the temp swings? If the cap releases where does if release from? Could it be the tank? I know there is a lot of info on the possibility of water pump and EGR cooler but I am confused as to why the tank would release into the engine bay?

It is a 2010 T5.1 Multivan 2.0TDI 132kW

[Silver Caravelle]

Hi there,

First step is to closely check for hose leaks ( including signs of coolant stain origin) to the expansion tank and to ensure tank cap is fully tightened ( with a slight resistance to the final turn). Also I have heard that tanks can very occasionally crack and leak. My brother's Audi A4 did twice! If no leaks and in relation to temp increasing and then dropping back to normal, it could be a sticking thermostat. Beyond that I suggest detailed investigation by a mechanic.

Regards,

Scott

[Sendo_VW_multivan_2010]

Best to go to a VW mechanic. Get a pressure test done. And they can also check for exhaust gases in coolant.
You do not want to muck around with overheating issues. If it is not the head gasket now, it soon will be.


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[scotinoz]

Bit of an update. Put a pressure test on the coolant system today and it appeared to be holding, may have been some slight drop off but there was no discernible leak anywhere. Ran the engine with the water pump return line disconnected from the expansion tank and there was a very weak flow coming out of it which suggests the pump is not circulating water.

[Silver Caravelle]

Hi there,

Do you think the water pump has a noisy bearing or is potentially weeping? In relation to the weak flow to the expansion tank, could it still be a sticky thermostat that may not be fully opening properly or early enough to operating temperature?

Cheers,

Scott

[scotinoz]

Hi there,

Do you think the water pump has a noisy bearing or is potentially weeping? In relation to the weak flow to the expansion tank, could it still be a sticky thermostat that may not be fully opening properly or early enough to operating temperature?

Cheers,

Scott

Sticky thermostat is a possibility but as I don’t know if the van has ever had a water pump and i was going to do timing belt in next 6000km I am going there first. Even if the thermostat was sticky when I first start the engine I would expect a decent healthy return flow to the tank

[Silver Caravelle]

I would expect the opposite in terms of little flow to the header tank when the engine is cold. That is the purpose of the thermostat. The thermostat will restrict flow to circulating coolant around the engine block only for quick warm up until the coolant warms up to then open the thermostat to allow coolant to then circulate through the cooling system. That is why I wondered about a sticky thermostat if the engine temp went intially high then settled back to normal. Now if there is little flow to the header take when engine is warm, it could be a number of things such as air locks, dodgy thermostat and possibly the water pump.
Anyway all the best with it.

[scotinoz]

I would expect the opposite in terms of little flow to the header tank when the engine is cold. That is the purpose of the thermostat. The thermostat will restrict flow to circulating coolant around the engine block only for quick warm up until the coolant warms up to then open the thermostat to allow coolant to then circulate through the cooling system. That is why I wondered about a sticky thermostat if the engine temp went intially high then settled back to normal. Now if there is little flow to the header take when engine is warm, it could be a number of things such as air locks, dodgy thermostat and possibly the water pump.
Anyway all the best with it.

Got someone to rev the van while I had the return disconnected and it definitely increased, suggest pump is spinning. Starting to wonder again about the sticky stat theory. Still need a gas test on the coolant to discount head gasket

[scotinoz]

Where is the thermostat on the 2.0 tdi 132kW?

[scotinoz]

Found it! Not sure what needs to come of to get it out though, looks buried in there

[scotinoz]

I would expect the opposite in terms of little flow to the header tank when the engine is cold. That is the purpose of the thermostat. The thermostat will restrict flow to circulating coolant around the engine block only for quick warm up until the coolant warms up to then open the thermostat to allow coolant to then circulate through the cooling system. That is why I wondered about a sticky thermostat if the engine temp went intially high then settled back to normal. Now if there is little flow to the header take when engine is warm, it could be a number of things such as air locks, dodgy thermostat and possibly the water pump.
Anyway all the best with it.

So you would expect little flow initially and more flow when warm?

[Silver Caravelle]

Correct, as it warms up one would it expect more flow as thermostat fully opens and pressure to then build in the expansion bottle when warmer. If it gets too hot beyond boiling temp, the coolant pressure is going to be relieved via the cap.
Ordinarily it should be below boiling point at 90c and no coolant loss through the cap ( the nature of a sealed cooling system expanding and contracting). So if there is good flow when warm to the coolant tank, it is unlikely to be the water pump unless it can be ascertained the pump is weeping or a noisy bearing. Where as a sticky thermostat is a cheaper option. Maybe remove the expansion bottle cap and run the engine an observe the flow into the bottle as it warms up. I think it will be visible to see coolant flowing/ returning to the bottle. But obviously put the cap on if the coolant starts flowing out of the bottle when warming up and avoid burning yourself in the process! I would be suspicious of a sticky thermostat given the initial higher temp and returning to 90c normal temp. Perhaps also monitor for a while to ensure no coolant loss. Of course if you still aim to change the timing belt and water pump given unknown history, all this will be checked as part of the process.

[scotinoz]

took the car for a drive today and all seemed fine, got home and stopped the van, checked the level looked ok so relieved the pressure by gently opening the cap. As I opened the cap as normal the pressure starts to vent but it vented underneath the bottle i.e. nothing coming out from the cap. Is this normal? Also while running I took off the oil cap and noted a good flow of air coming out here much more than I thought, is this normal?

[Silver Caravelle]

I am unclear regarding venting below the bottle? For example is it venting out of where the bottom hose clamps to bottom of the bottle; a possible leak there? I can only suggest look for dried coolant residue around hose openings to the coolant bottle to rule out any sort of leak and continue to keep a close eye on the coolant level that it is not disappearing somewhere.

If the temp is stable and seemingly no coolant loss and the thermostat is not sticking, perhaps monitor for the next few runs or check with a mechanic to be doubling sure.

After a good run there would be a 'minor level' of air flow bowing out of the oil cap opening. It is hard to gauge though without viewing it whether the level of air flow you indicate is normal though. If it is really blowing I would not consider this normal. Be worth a mechanic commenting on this as well.

[scotinoz]

I am unclear regarding venting below the bottle? For example is it venting out of where the bottom hose clamps to bottom of the bottle; a possible leak there? I can only suggest look for dried coolant residue around hose openings to the coolant bottle to rule out any sort of leak and continue to keep a close eye on the coolant level that it is not disappearing somewhere.

If the temp is stable and seemingly no coolant loss and the thermostat is not sticking, perhaps monitor for the next few runs or check with a mechanic to be doubling sure.

After a good run there would be a 'minor level' of air flow bowing out of the oil cap opening. It is hard to gauge though without viewing it whether the level of air flow you indicate is normal though. If it is really blowing I would not consider this normal. Be worth a mechanic commenting on this as well.

Found the venting location, the bottle vents through the cap but the liquid comes out one of the holes in the bottom which is as per design.