Coolant level mystery.

[Critical_Mass 10]

Hi all,

 

Got a bit of a odd issue with my coolant system.

 

Ive always known theres a minute leak of coolant coming from around the oil cooler (VR6), and i do mean minute. Last weekend, i was heading over to my parents when suddenly the water temp light came on, but the water temp was pretty good, it wasnt rising and stayed around 95 (hot day too), kept an eye on it and it was only about another mile to my parents.

 

Popped the bonnet when i got there and the coolant level was about 1.5 inch below the minimum level - i even looked round for any obvious leaks and there was none (bar the small one at the oil cooler) However, when i unscrewed the reservoir cap to top it back up and the level of the water raised once the pressure was released. Anyway i topped it up and when i got home i checked the level again and it was fine.

 

Today, i checked the level when i got home and again it had dropped. But AGAIN when i let the pressure out of the system the level went back up to normal. I put a little bit more though so it was just above max. But checking after a quick run the level was fine again.

 

Whats going on? Its been fine for ages even with a minute leak which doesnt even leak a litre of water in 4 weeks alot less then that.

 

Can anyone shine any light on this?

Edited April 27, 2011 by Critical_Mass

[Riley 0]

I wonder if by removing the cap, you are drawing air into the system (Through a small leak/Possible oil cooler?) which is pushing the coolant up?

 

Neil.

[boost monkey 0]

Yeah could be that. Also if you know there's a leak at the cooler why don't you just fix the seal or replace the cooler? You'd be impressed how much water can leak from a small dribble when the system is pressurised.

[Critical_Mass 10]

Cos i've been slack and not pulling my finger out! :lol:

 

If i remove the oil cooler i assume i'll lose oil and water? Will it be a case i'll lose a little of each if im quick on getting the part changed over. Or am i best to drain either/both?

[boost monkey 0]

well taking the cooler off will expose the oil lines, so the oil will dribble out first, and then taking the hoses off will leak the coolant.

 

I'm sure if you're methodical you won't lose too much of either :) The VR6 is different in that the cooler isn't sitting behind the oil filter like it does on the 4-cyl engines.

[Critical_Mass 10]

yeah true, i suppose thats a blesssing.

 

Checked the level again just before i left for work this morning. It has dropped again. But no sign of a leak ANYWHERE, not round the oil cooler, not on the floor not in the drivers footwell..... confused. hmmmm...............

 

oh and no signs of any steam in the cabin

Edited April 28, 2011 by Critical_Mass

[tony_ack 0]

With the leak, it could be a small drip when cold and under normal atmospheric pressure and not moving, but once the engine is running, the water is pumping around the engine, and the pressure increases, it could gush out of any small leaks.

 

Another possibility is that it could be leaking into the cylinders due to a faulty head gasket, but this isn't particularly common on the VR6 as far as I'm aware, and you'd have other symptoms too (steam from the exhaust when warm)

 

With the water level, the light in the dash is from the level sensor - hence why it is still running at the correct temp even if the light is flashing. The light flashed to tell you the coolant was low (which turned out to be correct!).

 

Also, the water rising up the expansion bottle when you remove the cap is completely normal behaviour - water (and the air in the expansion tank) expands when heated. Because the system is sealed (apart from your leak :-) ) the water cannot expand, and is pressurised. This is actually a good thing as it prevents the coolant from boiling at operating temperature. So, when you remove the 'expansion' cap (clue is in the name!) the pressurised air escapes, and the pressure on the water is released, allowing it to expand, and rise up the expansion tank. If the coolant is very hot when you remove the cap, then it will boil as it returns to normal atmospheric pressure and overflow, leading to burnt hands - I learnt this the hard way!

 

From experience, when you fix a leak on an old car, it just moves elsewhere. I changed a leaky crack pipe and thermostat housing last month. I replaced that, but ended up having to also replace the radiator and water pump a week later. As the crack pipe leak had been fixed, the system operated at normal full pressure again (i.e. there was no pressure relief from the leak), which finished off the weak water pump and rad.

 

---------- Post added at 10:09 AM ---------- Previous post was at 10:08 AM ----------

 

Actually - the reason it may be low in the morning is because you topped it up when it was hot? The coolant would contract as it cooled. You need to top it up when cold to get a true reading. The coolant leak could be minute as you say, and the level may have dropped slowly over time - you only noticed when the light came on. Then you opened the expansion tank when hot and it returned to normal, so you left it. The water contracted when cool, so you thought it had lost water again, etc., etc.

Edited April 28, 2011 by tony_ack

[Critical_Mass 10]

Cheers Tony, what you said makes sense and i understand the pressurised system etc. Ive topped it up when hot and this morning when cold too. Going to get undert the car tomorrow and take a look, with the engine running and hot.

 

This isnt what i need right now :-/

[boost monkey 0]

I don't think you're supposed to open the coolant system when it's hot are you? doesn't it say that on the cap?

[tony_ack 0]

I don't think you're supposed to open the coolant system when it's hot are you? doesn't it say that on the cap?

 

We were all young once...

 

Live and learn... live and learn :)

[Critical_Mass 10]

Took a look today and the minute leak on the pipe going from the crack pipe to the oilcooler is leaking more then i first thought. Its not gushing out even when engine running, but there was a lot of pink residue. Problem is there's not alot of room. But gonna have to get it sorted.