expansion vessel fills up and then when cool the level drops

Hello All
probably a simple answer and I have an idea of the cause but wanted someone in the know to provide a definitive answer.
Recently hit a deer on ns front not too hard but damaged fog light and dented bumper. All pushed out by hand and light on way to being replaced. Some time after the event I got a low fluid warning and then topped up the expansion bottle. Initially though I had lost water through the bump.
Level stayed fine and no more warning so I took the top off the expansion vessel and the level dropped quite a bit. Re filled to cold line and running fine, only thing I noticed is the level of bottle is quite high.
Is it possible the loss of fluid could be from the auto gear box cooler and if so is the fluid likely to go into the gearbox if it is dropping.
I want to sort it as soon as possible in case it is more of an issue than I think.
Any help or guidance would be gratefully received

Tony G

Go to the plumbers merchants and get a rapid system sealant.
Take off the top hose on the radiator and pour it in.
Then refit the hose and warm it up.
Some good quality stop leaks out there these days but avoid the automotive ones and go for boiler system ones.

Rock Basher said:

Go to the plumbers merchants and get a rapid system sealant.
Take off the top hose on the radiator and pour it in.
Then refit the hose and warm it up.
Some good quality stop leaks out there these days but avoid the automotive ones and go for boiler system ones.

Click to expand...

Hi Rock basher , before I do that, which seems to be a simple solution. What would cause the drop in fluid level if there is no evidence of leaks under the vehicle or in the engine compartment. I realise the sealant may well stop the water draining out but I am quite concerned as to where it may be going, particularly if it is something to do with the auto box cooling?

tony.g said:

Hi Rock basher , before I do that, which seems to be a simple solution. What would cause the drop in fluid level if there is no evidence of leaks under the vehicle or in the engine compartment. I realise the sealant may well stop the water draining out but I am quite concerned as to where it may be going, particularly if it is something to do with the auto box cooling?

Click to expand...

Absolutely don't listen to this moron. He's a troll given extremely damaging advice.

Nodge68 said:

Absolutely don't listen to this moron. He's a troll given extremely damaging advice.

Click to expand...

Hi Nodge68
Many thanks for the reply, do you know if there is an easy way to check the auto transmission fluid on my fl2 by any chance?

tony.g said:

Hi Rock basher , before I do that, which seems to be a simple solution. What would cause the drop in fluid level if there is no evidence of leaks under the vehicle or in the engine compartment. I realise the sealant may well stop the water draining out but I am quite concerned as to where it may be going, particularly if it is something to do with the auto box cooling?

Click to expand...

After not listening to moronic advice.

Take some sensible advice.
If you mean the coolant level varies with temperature, then that's correct. The cooling system level will change quite a lot on the coolant reservoir, as the engine capacity is quite large, and the reservoir volume quite small. Coolant naturally expands when hot, and contracts when cool. However there's another factor at play here, in that as the coolant temperature approaches 100° C the cooling system will pressurise, forcing the coolant in the system to expand the rubber hoses (of which there are many), effectively dropping the coolant level more than it expanded when it heated up. In theory all this expansion and pressurisation should balance out, but if the coolant is getting low, it can put the low level warning on.

How much coolant you are actually needing is the first stage to working out if there is an issue or not.

How much coolant have you actually put in and over how long?

Nodge68 said:

After not listening to moronic advice.

Take some sensible advice.
If you mean the coolant level varies with temperature, then that's correct. The cooling system level will change quite a lot on the coolant reservoir, as the engine capacity is quite large, and the reservoir volume quite small. Coolant naturally expands when hot, and contracts when cool. However there's another factor at play here, in that as the coolant temperature approaches 100° C the cooling system will pressurise, forcing the coolant in the system to expand the rubber hoses (of which there are many), effectively dropping the coolant level more than it expanded when it heated up. In theory all this expansion and pressurisation should balance out, but if the coolant is getting low, it can put the low level warning on.

How much coolant you are actually needing is the first stage to working out if there is an issue or not.

How much coolant have you actually put in and over how long?

Click to expand...

Nodge68 said:

After not listening to moronic advice.

Take some sensible advice.
If you mean the coolant level varies with temperature, then that's correct. The cooling system level will change quite a lot on the coolant reservoir, as the engine capacity is quite large, and the reservoir volume quite small. Coolant naturally expands when hot, and contracts when cool. However there's another factor at play here, in that as the coolant temperature approaches 100° C the cooling system will pressurise, forcing the coolant in the system to expand the rubber hoses (of which there are many), effectively dropping the coolant level more than it expanded when it heated up. In theory all this expansion and pressurisation should balance out, but if the coolant is getting low, it can put the low level warning on.

How much coolant you are actually needing is the first stage to working out if there is an issue or not.

How much coolant have you actually put in and over how long?

Click to expand...

Hi Nodge68
Thanks for that.

It may be that I am over analysing things. The first time it was low was after I hit a deer and a few days later I checked the inside of the engine bay etc and all looked fine. Then a low fluid light came on so I topped up with 50/50 water antifreeze to the cold fill level. It was only near the bottom of the bottle and this is what set the sensor off. I must admit I had not checked it for ages only a look to see each week and the level looked fine.
Then last week as a precaution when it was cold I took the top off and the level went down some more. not empty but towards the bottom of the bottle. Topped up again and all OK then checked today and the level cold was fine, took the top off and it has stayed as filled.
I think what was concerning me was that the first time I took the lid off after topping up, the water went down and I was trying to discover where it might have gone. In the absence of any drips or wet spots I thought the deer incident may have damaged the auto box cooler system and I was more concerned with fluids leaking into the gear box via the cooler.

tony.g said:

Hi Nodge68
Many thanks for the reply, do you know if there is an easy way to check the auto transmission fluid on my fl2 by any chance?

Click to expand...

Normally if you have a leaking trans cooler, the trans fluid will enter the coolant, and be very visible floating on the top of the coolant in the reservoir.

There are a couple of known coolant loss locations on these. One is the EGR cooler, which can pass small amounts of coolant into the exhaust after the engine is turned off. An EGR cooler leak can also cause coolant to become pressurised when the engine isn't hot enough to start to boil the water, but this symptom is hard to prove conclusively without checking for CO2 in the coolant. However it's also worth checking to see if there's any pressure in the cooling system first thing in the morning, as pressure held overnight is a clue that the pressure has come from somewhere other than coolant heating up.

My advice is to monitor the coolant closely, so you can get more data on the actual rate of coolant loss.

Nodge68 said:

Absolutely don't listen to this moron. He's a troll given extremely damaging advice.

Click to expand...

Now banned after previous warnings

+1 on the cooler.

Fluid will always flow from the higher pressure side to the lower and end up floating in the reservoir

tony.g said:

Then last week as a precaution when it was cold I took the top off and the level went down some more. not empty but towards the bottom of the bottle. Topped up again and all OK then checked today and the level cold was fine, took the top off and it has stayed as filled.
I think what was concerning me was that the first time I took the lid off after topping up, the water went down and I was trying to discover where it might have gone. In the absence of any drips or wet spots I thought the deer incident may have damaged the auto box cooler system and I was more concerned with fluids leaking into the gear box via the cooler.

Click to expand...

How much did the coolant go down by once you opened the system?
To me it's suggesting that the cap air admittance valve is stuck, so as the system cooled, it couldn't draw in air to take up the space, so the hoses contracted instead. Relaxing the vacuum in the reservoir by opening the cap allowed the hoses to return to the normal shape, drawing coolant from the reservoir as they did so.

My advice is monitor the the coolant loss, and go from there.

Nodge68 said:

Normally if you have a leaking trans cooler, the trans fluid will enter the coolant, and be very visible floating on the top of the coolant in the reservoir.

There are a couple of known coolant loss locations on these. One is the EGR cooler, which can pass small amounts of coolant into the exhaust after the engine is turned off. An EGR cooler leak can also cause coolant to become pressurised when the engine isn't hot enough to start to boil the water, but this symptom is hard to prove conclusively without checking for CO2 in the coolant. However it's also worth checking to see if there's any pressure in the cooling system first thing in the morning, as pressure held overnight is a clue that the pressure has come from somewhere other than coolant heating up.

My advice is to monitor the coolant closely, so you can get more data on the actual rate of coolant loss.

Click to expand...

Hi Nodge68
many thanks for the reply, I have not seen any fluid on top of the water in the reservoir but will treble check that before I start it today. I will be out in it today so will look first thing tomorrow to see if it is in fact pressurised.

On a side note I for some reason thought (probably mistakenly) the anti freeze was green in my bottle but I could be confusing it with my wife's car. The stuff I got from the motor factors is red and I have looked everywhere to ensure this is the correct stuff for my engine. Does the red stuff sound right to you?

blue beasty said:

+1 on the cooler.

Fluid will always flow from the higher pressure side to the lower and end up floating in the reservoir

Click to expand...

Hi Blue beasty
Thanks for the reply also, I will have a look in the reservoir to ensure it is only water and anti freeze mix not anything else.

tony.g said:

Hi Nodge68
many thanks for the reply, I have not seen any fluid on top of the water in the reservoir but will treble check that before I start it today. I will be out in it today so will look first thing tomorrow to see if it is in fact pressurised.

On a side note I for some reason thought (probably mistakenly) the anti freeze was green in my bottle but I could be confusing it with my wife's car. The stuff I got from the motor factors is red and I have looked everywhere to ensure this is the correct stuff for my engine. Does the red stuff sound right to you?

Click to expand...

Absolutely don't mix blue/green antifreeze with red coolant. They are two completely different fluids but do much the same job, except you can't put a mixture in the same engine. All vehicles after around 2002 should be using red organic acid coolant, not blue/green ethylene glycol antifreeze.

Nodge68 said:

How much did the coolant go down by once you opened the system?
To me it's suggesting that the cap air admittance valve is stuck, so as the system cooled, it couldn't draw in air to take up the space, so the hoses contracted instead. Relaxing the vacuum in the reservoir by opening the cap allowed the hoses to return to the normal shape, drawing coolant from the reservoir as they did so.

My advice is monitor the the coolant loss, and go from there.

Click to expand...

Hi Nodge68
That sounds like a very feasible answer, I will check where the level goes to when hot and where it is when cold tomorrow, perhaps it may be as simple as a new cap for the reservoir and my over worrying will be put to rest. In any case thanks for the advice. Regards
TonyG

Nodge68 said:

Absolutely don't mix blue/green antifreeze with red coolant. They are two completely different fluids but do much the same job, except you can't put a mixture in the same engine. All vehicles after around 2002 should be using red organic acid coolant, not blue/green ethylene glycol antifreeze.

Click to expand...

Hi Nodge68
I think I must have remembered it wrong myself, when I bought it a few years back the first thing I did was get the cam belt and water pump changed and the guy I used was a decent mechanic so I am certain he would have used the right stuff. I think it must be something to do with my age, He he

tony.g said:

Hi Nodge68
I think I must have remembered it wrong myself, when I bought it a few years back the first thing I did was get the cam belt and water pump changed and the guy I used was a decent mechanic so I am certain he would have used the right stuff. I think it must be something to do with my age, He he

Click to expand...

If it's had a replacement belt and water pump, then the mechanic would have put the correct coolant in it, as pretty much every vehicle since the early 2000s would use OAT (red) coolant.

I wonder if the mechanic tightened up the drain plug on the pump when it was installed? On a lot of replacement pumps, the system drain plug isn't snugged up tight, allowing just the tiniest amount of coolant to creep out and evaporate away unseen. Every pump I've seen over the last few years has needed the drain plug to be correctly tightened on pump fitting. Just a thought as to where the coolant might be slowly disappearing from.

Nodge68 said:

If it's had a replacement belt and water pump, then the mechanic would have put the correct coolant in it, as pretty much every vehicle since the early 2000s would use OAT (red) coolant.

I wonder if the mechanic tightened up the drain plug on the pump when it was installed? On a lot of replacement pumps, the system drain plug isn't snugged up tight, allowing just the tiniest amount of coolant to creep out and evaporate away unseen. Every pump I've seen over the last few years has needed the drain plug to be correctly tightened on pump fitting. Just a thought as to where the coolant might be slowly disappearing from.

Click to expand...

Hi Nodge68. I will have a look at the pump some time soon as I am planning to take the inner wheel arch linings out to check for any rust or mud etc, I will probable need to do this to re fit the fog lamp hold on the n/s anyway so doing both will be no issue.
The leak issue has only been evident (at least to me) recently and the pump was done a couple of years back. Still it is worth checking as a source of the problem.
Many thank for the replies and I will post any further answers re this in due course, have a good weekend.
TonyG

tony.g said:

Hi Nodge68
Thanks for that.

It may be that I am over analysing things. The first time it was low was after I hit a deer and a few days later I checked the inside of the engine bay etc and all looked fine. Then a low fluid light came on so I topped up with 50/50 water antifreeze to the cold fill level. It was only near the bottom of the bottle and this is what set the sensor off. I must admit I had not checked it for ages only a look to see each week and the level looked fine.
Then last week as a precaution when it was cold I took the top off and the level went down some more. not empty but towards the bottom of the bottle. Topped up again and all OK then checked today and the level cold was fine, took the top off and it has stayed as filled.
I think what was concerning me was that the first time I took the lid off after topping up, the water went down and I was trying to discover where it might have gone. In the absence of any drips or wet spots I thought the deer incident may have damaged the auto box cooler system and I was more concerned with fluids leaking into the gear box via the cooler.

Click to expand...

You may have a crack in the expansion vessel ...

Dippypud said:

You may have a crack in the expansion vessel ...

Click to expand...

Hi Dippypud
I will double check the vessel too, I have had a look today after a drive out yesterday and the level seems to be the same with no drop when the lid is removed. It may be a really small pin hole or a crack in something that only becomes evident when the water gets a lot hotter. It was cold yesterday and I did not drive very far so we will see how it goes.
I still need to get the fog light housing repaired and re installed and maybe once the inner wing is removed something may be more evident.
Thanks for the reply
TonyG