Overflowing Overflow tank

[jazza21]

Just discovered a new little problem (or maybe it's a big one). Here goes, it's a long story, but as far as I can tell there's no other posts directly relating to this.

I noticed a pool of coolant in front of my car when I went back to it at a shopping centre today. Thought little of it, it seemed to be drying out like it was from the previous car parked there. Anyway I drove home, parked car on the street and went inside. Was home for maybe an hour and went out to my car to go for a drive. Sure enough there was the coolant again... So I topped up the overflow tank to the MAX level (it was empty) and checked if I could see where the leak had come from. No leaks anywhere but the liquid seemed to have only come from the overflow hose that goes down to the road. Went to a mates place a few K's away, parked car, went upstairs for 20 minutes, back to car, no leaks... So I assumed it was alright. Anyway next drive, next car park, check for leaks before I go, all seems fine. Went to a movie, came back about 3 hours later and there it was again, all across the car park, and this time there was no doubt as to it's origin - the only place any liquid was expelled was the overflow tank's extra overflow hose (the one that leads down under the car to the road).

I replaced the whole tank a few months ago, new cap, whole system flushed, checked and rechecked. All OK. The remaining coolant in there now is bright green, no discolouration, no oiliness, just less of it still in the radiator. The tank itself and all the normal hoses etc. are not showing signs of deterioration or fluid loss.

The only thing I can put it down to is remaining pressure when I turn off the car, which forces extra coolant up into the overflow tank, which fills it too much then goes out the other pipe to the ground. The car has not been overheating and is otherwise running just fine.

I really need some help here with this one. Other than going for a preasure test I have pretty much exhausted all options I can think of.

Any suggestions?

Jazza

 

[Demons1964]

I've been down this path recently with my wife's car (exact same symptoms and for your sake I hope it's a different fault!). So, a few questions for you first. Is it a V6 or V8? Are the trips you're making more than a few km's (i.e. is the thermostat given enough time to fully open)?

It appears your cooling system is doing what it's designed to do: bleeding off excess pressure through the overflow tank. But the question is where is the excess pressure coming from?

Given that it's a new cap and assuming that you have bled all the air from the system then you start with the simple stuff before progressively replacing smaller cheaper components until the big dollars come out to play. So, first off have you checked your computer for fault codes (i.e. coolant temp sensor faults if a V6)? If all ok, next step is to check out the thermostat (remove from car and check if it opens in boiling water). Let me know how you go.

Mark.

 

[AnthsVSLexcen]

the same thing happened to me a few weeks ago. I replaced my thermostat and flushed the system and now its fine. I got told that this happened because there is too much pressure in the cooling system and it only started over flowing now because of the hot weather and maybe because there was more pressure on the cooling system if you used the air-con etc.
hope this helps
Anthony

 

[jazza21]

I am wondering if it is even a dodgy tank cap that's causing my problem.

I wish I had more tools and time to fix it easily! I have limited resources (now that Dad's moved north) so I have to do everything with the few things I have

I guess I'll have to pull out the manual and read it to get the thermostat off.

Still the leak hasn't happened again so far as I can tell, but I have no idea if it's doing it when I am driving.

Jazza

 

[hako]

Remember that the overflow tank is an 'overflow' tank.....check the coolant level at the radiator cap on a cool engine and if it is full then you should have no problems. You may be overfilling your overflow tank. Normally the overflow tank will not require topping up more than once a year as the only way the coolant is lost is thru evaporation.

 

[aa23]

I would have thought that if the overflow tank (catchment tank) is filling up too often, it's because it's being fed too much fluid. The only reason it would do that is if the radiator cap is not sealing and holding the pressure in. When there's too much pressure, it is designed to let the fluid flow out, rather than place excess pressure on the more expensive parts. As the pressure drops, eg: cooler, in theory the fluid is supposed to be drawn back out of the storage tank, therefore stopping the cooling system from running low, and keeping the system full of flid, and not air.
So, I'd check the radiator caps ability to open and close correctly. Not sure how, but it's where i'd start.
And if i'm totally wrong, I'll just slink quietly away. :yeah:

 

[jazza21]

I think you're right on the mark aa23. I have put the problem down to the heat we've had recently and the excess preasure building up from that. I looked at the tank lid and it looks ok but who's to say what looks right really is? Since posting last I have been checking all the time and the problem seems to have subsided.

I know the correct level of coolant I need to put in and I know it was never overfilled. I guess I just have to wait n see now.

Dad suggests it's a similar problem to VL's (Overheating due to the aircon's positioning and follow on effect of too much heat equals boil-over). I think I will just have to live and learn and buy the real deal Holden Coolant when I do the next flush.

Jazza