Hello Forum
I have an annoying problem whereby I am losing coolant from my expansion bottle, the coolant is coming from the cap on the bottle. I have just replaced the cap with a new one and the problem is still there. I only have to travel a few miles for the water to leak from the cap. It would appear that there is too much pressure in the system. Has anyone had the same problem or any idea what is causing coolant to leak from the cap?

I have checked the hoses attached to the expansion bottle by disconnecting them and blowing into them and found no blockage. I also blew into the small outlet and filler hole on the expansion bottle and yet again no blockage. I drove to work this morning at 7am and when I went home at 5.15 I checked to see if the coolant level was okay, however I was unable to remove the cap as there was still a lot of pressure left in the system from the morning. I decided to whack the heating on full on the way home to see if this made any difference. The only thing I achieved was to make myself sweat buckets. Please can someone suggest what else could be wrong or what I should check.

 

Are you sure the tank does not have a crack?
Has the tank been replaced? They almost all fail with heat and time.

We need your car details to help.
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My car is a 2003 2.5. The water is most definitely leaking from the filler cap on the expansion bottle.

 

I have just been advised to bleed the cooling system. Can anyone tell me where to find the bleeding points?

 

There is a bleed screw on the top of the expansion bottle - on the 2003 3.0L - we didn't get the 2.5L over here.
I'm not saying you're lying to us...but I reckon your leak is at the bottom of the nipple that comes out of the filler-neck and connects to a hose that leads to a little tank-turret-looking port on the upper rad hose. It tends to crack right at the neck on the underside and looks for all the world like the cap is what is leaking.


Mending it means a tank replacement. Next time it is time to renew your coolant, go ahead and renew that upper rad hose, too, if it is original. It will spring a leak soon at that overflow hose port. You can swap the expansion tank for a new one without much coolant loss, so no great advantage in combining an upper hose renewal with that job - unless you decide it is time to renew the coolant also. Don't commence that upper hose swap until you obtain a flexible hose-clamp pliers, though.

 

[ Thanks for the info. The leak is however definitely coming from the cap. There is way to much pressure in the system. I have tried the bleed screw and will let you know if its made a difference.

 

You need to find out why there is excessive pressure in the system by concentrating on looking for a blockage. Unless you've recently changed the coolant it seems unlikely that you'll have an air lock. When you manage to remove the cap, have you seen any air bubbles in the coolant? The coolant loss from the pressure cap is just a consequence of the excessive pressure. You shouldn't have any problems at all removing the cap 10 hours after using your car. I've recently put a new radiator on my 2003 3.0 and could easily remove the cap 30 to 45 mins after running the car up to full temperature.

 

In that case, the cap isn't leaking; It is performing its function as designed. Are you monitoring coolant temp via the OBD port? Or maybe put the IP in Engineering Test mode prior to each start so you can see it? Elevated pressure is only available due to elevated temperature. (It's not like your water-pump became SUPERtron all of a sudden...) So whatever the boiling point of your coolant mix is at 15 psig is what you are getting to. (if you are running distilled water at sea-level, then your actual coolant temp is hitting 227 deg F -somebody check my science! I seem to recall +1 deg/psi above std press - but think maybe I've confused it with 1 deg less in BP for each 1000 ft of alt above sea-level - but in any case, you are exceeding 212) You may be overheating as you drive it. I believe the 3.0L has some built-in protections and won't cook itself, whereas the 4.0L doesn't, and will be happy to cook itself into a molten mass. I know nothing of the 2.5L - but you may want to develop a way to see the actual coolant temps* if you need to continue driving it until you get it sorted. Many have reported their needle on the dash stays in the "normal" range well beyond what they consider "too hot."

*If you do have an air-pocket..and if it is around the sensor, your guage and/or OBD indication may be very inaccurate.