Filling the reservoir

[944cabby]

I always make a point of filling the rad water reservoir in my cab to the max level but whenever i do it always seems to drop to bang in the middle of "max" and "min" withing a very short time ie a couple of "spirited" drives.
I spoke to a chap some time back who claimed that this was perfectly normal for 944's and was nothing to worry about as long as the reservoir wasn't completely emptying very quickly.
Is this correct and if so am i overfilling?

 

[sawood12]

The engine cooling system is (or should be) a sealed system. Where is the lost fluid going? However it is strange that you lose fluid to a certain level. Are you sure you can't spot a leak somewhere, say at the height of where the level settles? Or is it just an illusion due to the strange shape of the expansion tank similar to the varying rate at which your petrol gauge drops? Maybe if you left it longer the level would continue to drop and a much slower rate?

 

[Riverside]

Mine does the same, it normally sits just above minimum & doesn't lose any more water than that.

I think as long as the level 'settles' to a consistent position you shouldn't worry, I'd be a little concerned it it settled below minimum though.

 

[sawood12]

Is there some sort of pressure reliefe valve in the system? Maybe when you fill it upto the max there is too much fluid in the system and when the pressure builds up some fluid vents off and settles at the level it does. I wonder if the concentration of antifreeze increases as the water steam is vented off increasing the antifreeze concentration (assuming it has a higher boiling point than water).

 

[Guest]

My 944 also settles to just above the minimum mark in the expansion tank...I'm glad its not just mine as i was getting worried! The car doesn't overheat or anything, so I can only assume this is "normal"....

 

[Riverside]

ORIGINAL: sawood12

Is there some sort of pressure reliefe valve in the system? Maybe when you fill it upto the max there is too much fluid in the system and when the pressure builds up some fluid vents off and settles at the level it does. I wonder if the concentration of antifreeze increases as the water steam is vented off increasing the antifreeze concentration (assuming it has a higher boiling point than water).

The coolant header tank cap has a pressure relief valve in it (it's a bit like a thermostat but for pressure instead of temperature - take it off & have a look when the car is cool & you'll see there is a spring loaded seal. When the pressure is too high it overcomes the spring pressure so coolant can escape in a controlled manner) which allows excess coolant to exit via the thin black vent tube that connects to the filler neck. If the cap is old & weak it may 'open' the valve too soon & allow excessive water loss, however if the fluid level settles at a particular level then basically it's working as it should. If there were no pressure relief valve & the car were to overheat the weakest link (probably the bottom hose) would burst & pressure would be lost in an uncontrolled way.

The concentration of antifreeze does indeed affect the boiling point of the coolant, it raises it (it also lowers the freezing point) which is why you need the correct ratio (50:50) even in summer. The correct type of antifreeze also helps to reduce corrosion in the coolant passage ways in the block, corrosion can reduce cooling efficiency and restrict the flow too.

Neither of these points are specific to Porsches but the 944 has a relatively low amount of coolant stored in the reservoir compared to more mundane cars (primarily to save weight I believe), so it's important to check the level regularly and familiarise yourself with your car's normal behaviour.

 

[zcacogp]

ORIGINAL: Riverside

... you need the correct ratio (50:50) ...

That sounds like a very concentrated solution ... the antifreeze bottles usually say 1 part in 4 or 1 part in 5, I believe. Are you sure about this?

Also, another question. My local Euro Car Parts sells two types of antifreeze - "blue" and "pink". I am assuming I should use "blue", as it is the type that VW's of that age used. (They switched to "pink" later on.) Is this correct?


Oli.

 

[dlknight]

Hi Oli,

I think 50:50 is what I used when I changed my coolant last, not sure where I got the figure from maybe Haynes or the back of the coolant bottle. I used the VAG pink coolant as it is recommended for ALL engines including aluminium blocks such as ours. I don't think you can get the blue coolant anymore from VAG....

Regarding the coolant level dropping in the header tank, mine used to also do this and always settled just above the minimum mark. I have recently had the radiator replaced with a brand new one however and the level is now settling at a higher point just below the maximum mark... thinking back I may have had a slight drip from the old radiator and the core didn't look too great after removing it.

Regards

Dave K

 

[Riverside]

ORIGINAL: zcacogp

ORIGINAL: Riverside
... you need the correct ratio (50:50) ...

That sounds like a very concentrated solution ... the antifreeze bottles usually say 1 part in 4 or 1 part in 5, I believe. Are you sure about this?

Also, another question. My local Euro Car Parts sells two types of antifreeze - "blue" and "pink". I am assuming I should use "blue", as it is the type that VW's of that age used. (They switched to "pink" later on.) Is this correct?

Perhaps you are thinking of windscreen washer fluid for the ratio? 50:50 is correct for coolant.

My understanding of the type of antifreeze to use is that blue is the correct type for a 944 but you can use red, but don't mix blue & red. If you mix the two types apparently the solution gets thicker (jellifies) which is a Bad Thing so for topping up use whichever colour your car has in it already. There is also a third type of antifreeze which is green, I don't know anything about it though. Blue is the cheapest & most common anyway so I've never looked into it any further. If you can't tell which colour is in the car change the coolant.

 

[jr2015]

The coolant level should be at "max" when the engine is at working temperature, if you fill to the max mark when the engine is cold you`re overfilling and the excess will be evacuated by the pressure cap system while driving. When correctly filled, the level will be approximately half way between max and min when the engine is cold as fluid is drawn into the engine as everything cools down and expands to fill the expansion tank as the motor warms up ( that`s why its called an expansion tank ). The exact level will vary from car to car as the efficiency of the pressure cap, condition of the radiator ( silted up), and whether there`s any air in the system ( and mine can be a b*stard to purge completely) can vary.
50/50 is the water: antifreeze ratio I`ve always filled up with as its good for something like -33 celcius, easier to mix, and perhaps most importantly a strong anti-corrosive.I always buy " universal" grade, its blue I think.I`ve never bought the Porsche product as its made to the same BS or SI but costs much more.
Hope this is helpful.
jr.

 

[944cabby]

Thanks for the replies chaps - i'll leave it as it is and see what happens from now on.

 

[TTM]

Coolant tanks tend to got out of shape and change colour with the number of warming up and cooling down cycles. I have seen many that suggested were empty but were actualy correctly filled, so the "correct" coolant level can vary between cars ...

 

[sawood12]

ORIGINAL: jr

The coolant level should be at "max" when the engine is at working temperature

Are you sure? Isn't it the case that the level tends to drop when the engine is at operating temp, in fact it is possible and normal for the coolant level to drop below the minimum mark at operating temp. As the engine warms up and the temp of the coolant rises the pressure in the system increases and the air in the expansion tank expands and pushes the fluid level lower (air expands much more than water when hot). You should alway top up the engine coolant when the engine has cooled and the pressure in the system normalised.

 

[jr2015]

Hi Scott,
The water in the engine water jacket expands as the engine gets warm and the level in the expansion tank rises to the max mark,( this is based on observation over the last 15 years), as the engine cools the coolant is drawn from the expansion tank back into the water jacket.No hot air from the engine arrives at the expansion tank because ideally there should be no air in the water jacket unless the system needs purging, As the tank level rises, the air escapes through the relief system if pressure becomes excessive. It`s a sealed system so that the boiling point of the coolant is raised thus preventing steam creating "hot spots " in the engine.
Page 48 of my vehicle handbook (1983 model) states the level should be between max and min when engine is cold.
jr

 

[John Sims]

ORIGINAL: sawood12

...... As the engine warms up and the temp of the coolant rises the pressure in the system increases and the air in the expansion tank expands and pushes the fluid level lower (air expands much more than water when hot). .....

No it doesn't as you can't compress water unless there are air pockets in the system in which case it is the air in the pockets which would be compressed. But if there were air pockets it is more likely that these would expand more than the air in the header tank.

However the coolant does move in the expansion tank as the turbo cooling pump sucks water from the bottom and squirts it in at the top. The drop you are seeing is the water being pumped into the pipe above the turbo cooling pump on its way back to the header tank.

 

[sawood12]

I'll take your word for it JR, I always thought that the increase in pressure overcame the thermal expansion of the water (water doesn not expand that much) and lowered the water level. I.e. the term Expansion Tank was more in reference to the giving the air a space to expand without forcing itself into the water jacket rather than giving the coolant a space to expand into. I'll have to take a look the next time I have the bonnet open while the engine is hot - although it'll have to be in my Focus as I can't see the fluid level in my standard issue stained 944 expansion tank!

 

[Hilux]

Mines always just above the lower level. I`ve topped it up many times and it always comes home at that level so now I dont bother anymore about it.

With the average family run about you tend to check it when the light comes on or when your occasionally under the bonnet. i feel that as we love the cars and fuss over them we tend to notice more the small fluctuations and variations more than most.

This can be a slippery slope as then the worry grows, we lie awake at night, we cant concentrate at work and then................


.............................the decision is made, out with the engine, I`d better check the head gasket oh and while I`m in there I`ll renew the pump, oh go on I`ll put in a really hairy cam and solid lifters but if I do that I`ll need stronger con rods and then the bearings will need new ones and I`d better cross brace the block and get a stronger crank, and what about the extra power? I`d better uprate the brakes and if I`m going quicker I`ll crash harder so do I get 3 or 5 point harnesses, oh no I`ve no where to fix them so I`ll fit a roll cage so out with the interor to weld it in so it`ll need a complete respray and if its a bare metal shell then I`ll lighten the loom so I can throw away all the electrics so I`ll need Recaros and Momo and Sparco catalogues and I`ll talk to the bank manager about a re-mortgage..........................................

You`ve been warned..............................

DO NOT PEER TOO CLOSELY INTO YOUR EXPANSION TANK []

 

[John Sims]

So true Paul.

In a similar vein....."If it ain't broke, fix it till it is."