is it the cap?

[coetzeeh]

I noticed a while ago that the coolant level in the expansion tank no longer remains at the same level (which it used to do). When checking I found the level higher up in the tank. I also noticed some blue coolant on the expansion tank 'shoulder'.

I let the car idle with the expansion cap off and noticed some bubbles/air venting, and after the car cooled down, the level had dropped right to the bottom. I topped up to mid way.

The level in the swirl pot is right at the top.

Today, after a nice long run, I parked and opened the bonnet. I could hear a very faint hissing noise from the expansion cap - as if it was venting.

The car temp never reached 90 (in fact hardly went over 85 even in traffic), the fans kick in etc etc.

Before I rush out and buy a new cap - should I be able to hear the hissing/venting noise from the expansion tank cap? (the blue one).

ps - the rad is 3 years old, and I can not see any steam from the rad or leaks from the coolant pipes.

[AC Motors]

Somewhere you have a small leak, I had the same problem, eventually I could see a small puddle below the rad, eventually found a very fine jet escaping from the Rad which was almost invisible. It may be very difficult to find but I think you have the same problem. (I assume you checked the oil cap for milky residue indicating head gasket failure & water loss). If you have the heater on can you hear 'gurgling and bubling' inside the car? This indicates air getting into the system. Hope this helps, good luck.

[Rob_the_Sparky]

Worst case is a bust head gasket...I don't know about the Rover V8 as I've not had my car that long but on wet liner engines (like my Peugeot) the headgasket almost always fails between water jacket and piston resulting in unexplained loss of coolant and pressurisation of the coolant tank even with a cold engine. It can be a subtle loss initially as well.

However, do not panic this can be tested for (leakdown or compression test) and a Rover expert may be able to say how likely this is on the V8.

Unexplained water loss can also be a water pump seal or as the previos chap said a fine leak somewhere.

In my experience a cap that is no longer pressurised will not lead to a loss of coolant, especially in this cold weather, and I've run cars with the pressure cap intentionally part open (due to dodgy hoses and radiators).

Rob

[TVR Beaver]

If the level is going up.. gas is getting in... when you looked for the bubbles.. did they stop after a while?.. or keep on coming?.. I can't see how a hole in a presurised system can allow gas / air in... only when cooling when you could get negative pressure?.. If the bubbles keep on coming... it sounds like head gasket (or others I won't even mention!)...

[coetzeeh]

The bubbles stopped after a minute or so.

I had the same symptoms 4 years ago and it turned out to be the rad that needed replacing. I was hoping that a recored rad would last a bit longer...

I need to go and chaeck the levels after the car cooled down.

[Bluebottle]

coetzeeh said:

The bubbles stopped after a minute or so.

I had the same symptoms 4 years ago and it turned out to be the rad that needed replacing. I was hoping that a recored rad would last a bit longer...

I need to go and chaeck the levels after the car cooled down.

system has a gas/air leaking into it.
Hydro carbon tester syringe should rule out a head gasket issue, most garages have one so a 5 min check of the coolant at any local garage. Head gaskets can leak without any overheating or other normal signs when a compression ring fails which can pressurise the water jacket. I would expect you to be losing water out of the expansion tank when driving which would leave water droplet staining around the top of the expansion tank (not a blue cap issue, its what its meant to do if the system over pressurizes).
Your description indicates a more likely case of coolant system leak...Could be rad again, but worth pressurizing the system to check for leaks elsewhere in the pipework. I once had a leak from the blanked off pipe coming off of the inlet manifold which only leaked at high rpms took month to figure out where the leak was, simple pressure test i would have found it straight away.

[TVR Beaver]

Well if the bubles stop that is good news... Do you have a cap with one or two valves on it?.. The real unit should let air in whilst cooling as well as air out at 1 bar when heating... If it's only the 'out' type (like I use at 1.3 bar) it will (could) go negative pressure when cooling and draw air in from any holes / leaks in the system. (to add to this, the leak can also act as a one way valve as with possative pressure you may not get the joint / hole / leaking... but will allow air in at negative pressure..) This air when heating / moveing again will show as bubbles for the first few min's until clear and will also result in a high fluid level when cold as air has been drawn into the system as some point.
The hard bit now is to find where it is... I'd get the sniffer on it anyway just to make sure but sounds like you are drawing in air to me.. Good luck!

[coetzeeh]

I had a look a few minutes ago and the coolant level has not moved since I topped it up before my last trip. Level is approx mid way in the tank.

I'm going to drive it a keep a close eye on the coolant after every trip.

The car is due a service so I'll ask the good people to check the cooling system regardless.

Thanks for all the help so far.

[coetzeeh]

Update - I took the Griff on a 200 mile round trip this week. The coolant level has not moved sine I got the air bubbles out prior to the trip.

The only thing I can think of is that I did not tighten the blue exansion tank cap properly and hence some of the coolant ended on the expansion tank shoulder. Not sure if this would have caused any air I saw bubbling out when I ran the car with the cap off though?

I'm sure this was just the Griff keeping me on my toes

[737 FLF]

I had a similar fault a while ago. Bought a new cap for £2.50 from

http://www.gsfcarparts.com/branches.html

Job done.

[AC Motors]

The cap is a standard VW/Audi part which you can buy over the counter at most dealers, got mine form an Audi dealer, about £4.50 I think, you need a part number though.