Coolant issue

bear1

Over the last 2 weeks I've been having a weird coolant problem.
Went to the car one morning and saw coolant pooling under the car, popped the bonnet and saw it was low so topped it up and booked it into my local mechanic for diagnosis.
Few family issues got in the way and I completely forgot about the issue.
A few days ago my wife took the car and called me to say that the coolant warning light was on and came back.
Popped the bonnet again and saw it was empty. I refilled it and remade the appointment for this week.
Now I'm noticing that my temperature guage is acting strange where it slowly goes up but usually if im accelerating, if I decelerate then the temperature goes down.
Stopped the car again tonight to check the severity of the leak and saw it was again empty, but when i opened the reservoir the coolant came back in..
It's going in this week to get it fixed but just wondered if anyone ever encountered something like this?
Passat B6 tdi.

Supergurrier

Sounds like you have a leak or crack somewhere in the system and only low temperatures and high pressure are causing intermittent leaks

bear1

Supergurrier wrote: »

Sounds like you have a leak or crack somewhere in the system and only low temperatures and high pressure are causing intermittent leaks

I was wondering if possibly the thermostat is failing which may be causing it to lose coolant?

FortySeven

bear1 wrote: »

I was wondering if possibly the thermostat is failing which may be causing it to lose coolant?

Could be a crack in the thermostat housing. Not sure if common on your engine but common on fords. I think your coolant temp sensor is on there too so a crack could explain varied temp readings if pressure is pushing coolant out of the crack under load. This could throw the sender readings.

delly

bear1 wrote: »

I was wondering if possibly the thermostat is failing which may be causing it to lose coolant?

Coolent is in a closed system. If you have to refill, then there is a physical break or crack somewhere that is letting it out. A thermostat can't cause that if good or bad.

Supergurrier

It's common this time of year for a crack on a plastic component or for a hose to split as the temps go up and down when car is started and shut down etc, i would be looking at that. As said if it's only happenning now nd again it's not towards the bottom of the system and more than likely only happenning under engine load.

BrianD3

A coolant reservoir emptying over the course of a few days with a wet patch under the car is generally due to a leaking water pump in my experience of other cars.

The behavior of the gauge doesn't sound particularly strange to me if the water pump is leaking or even if it isn't leaking. You may be paying closer attention to the gauge now as you know there is a problem.

If the reservoir is empty but there is still coolant in the system, it is likely that coolant will flow into the reservoir if you open the cap when the engine is hot.

bear1

Water pump was changed for a OEM part during its timing belt change this February so I doubt it's the pump failing after only 9 months.
But I'll have it looked into, A hose was also replaced during the year as it had cracked and letting coolant out. This also was replaced with a genuine VW part.
Hoping it's the same issue but just can't understand why the thermostat is lowering the temp of the car when I'm slowing down.
I can cruise at 160 and it will be at 90 degrees but if I start slowing down then the temp goes down too, never had a car do this to me before.

jca

Get the leak sorted first. Hopefully running it very low on coolant hasn't blown the head gasket, although I think it has. Try running the engine with the cap off the reservoir and it topped up to the max line and check for bubbles appearing in the coolant as it heats up.

Tails142

Yeah stop driving it with no coolant, just in case nobody has said this to you.

TallGlass

If it's that water pump you'll lose the heating inside the car. My guess is a crack in the block somewhere if there's no coolant leaking onto the ground. Is the oil it's normal colour?

bear1

jca wrote: »

Get the leak sorted first. Hopefully running it very low on coolant hasn't blown the head gasket, although I think it has. Try running the engine with the cap off the reservoir and it topped up to the max line and check for bubbles appearing in the coolant as it heats up.

Tails142 wrote: »

Yeah stop driving it with no coolant, just in case nobody has said this to you.

TallGlass wrote: »

If it's that water pump you'll lose the heating inside the car. My guess is a crack in the block somewhere if there's no coolant leaking onto the ground. Is the oil it's normal colour?

I'll clear the first two posts up.
The car has a sensor when the coolant gets below a certain amount but coolant will still be in the reservoir just it will be minimal.
It dings the message when you start it up so except for one instance the car was topped up with coolant.
Oil is a normal colour and there is no mayo colouring under the reservoir cap.
As for the 3rd post, no the heating in the car is fine and there has been signs of coolant leaking under the car so potentially a split pipe? I hope..
Oil is normal.

bear1

Got the car back from the mechanic yesterday and he said they couldn't locate any leak or anything which pointed to it leaking.
So they bled the system to remove any air and then left the car running for a while and nothing happened.
Took it for a spin and again, slow to warm up and then guage can't decide what temperature it wants to be at.
Starting to think that the thermostat is busted and weirdly it seems to do this only in cold weather.

FortySeven

bear1 wrote: »

Got the car back from the mechanic yesterday and he said they couldn't locate any leak or anything which pointed to it leaking.
So they bled the system to remove any air and then left the car running for a while and nothing happened.
Took it for a spin and again, slow to warm up and then guage can't decide what temperature it wants to be at.
Starting to think that the thermostat is busted and weirdly it seems to do this only in cold weather.

These kind of issues can be a pain in the hole. Still, saying that, why did your mechanic not remove the thermostat and test it? It's simple enough to do and would have confirmed failure.

Did they plug the car in to check for any sensor fault? Most garages would have some kind of diagnostics and even the generic ones like Delphi, Worth wow etc would allow live diagnostics which would rule out a sensor malfunction.

bear1

FortySeven wrote: »

These kind of issues can be a pain in the hole. Still, saying that, why did your mechanic not remove the thermostat and test it? It's simple enough to do and would have confirmed failure.

Did they plug the car in to check for any sensor fault? Most garages would have some kind of diagnostics and even the generic ones like Delphi, Worth wow etc would allow live diagnostics which would rule out a sensor malfunction.

No idea, the only thing he said was that they had the car running for 2 hours (the massive drop in fuel I have seems to prove it) and not a drop left the expansion tank so he suspects that the coolant was coming out of the tank.
For now I'm going to keep checking the levels and if it starts dropping again.
Hate when this **** happens.