Suspected leaking radiator - Ford Fiesta 2001

[mundo]

The anti-freeze level keeps going down and I am putting about half a litre of ready mixed anti-freeze every week or so. When the car is parked I have noticed a wet patch on the ground underneath the radiator (which is definitely anti-freeze) but the garage has pressure tested the radiator and cannot find a leak.

Seems a bit of a mystery this one. If it's had a pressure check and that has been OK then what else could be causing the leak?

 

[keyplayer]

With the staining qualities of antifreeze you should be able to see where it's been leaking. Did the garage pressurise system whilst both hot and cold? Hoses have been known to leak when cold but reseal when hot. And possibly your header tank cap is faulty.

 

[mundo]

Could be the header tank cap, I'll have a look at that and see if I can see where it appears to be leaking from. I might try and post a few photos which should help.

 

[mundo]

I've been having a look for this radiator cap and I am non the wiser . I've even studied the Haynes manual and can't find it in there.

I'm assuming that this is actually on the radiator and not the expansion tank cap? If so then can you tell me where exactly it is.

 

[Glassman]

I think the only screw on cap on the radiator is the drain plug which is situated at the bottom of the radiator. You'll find it if you jack the front of the car up slightly and look from underneath the car. It's only a small plug and you can usually undo it with a 1p coin. Other than that, perhaps you should get somebody else to pressure test it next time?

 

[mundo]

Where can I get a new screw on radiator cap from? Is this the type of thing I can pick up from halfords or would I need to pay an extortionate fee from a ford dealer? I suppose I could get one from a scrap yard but that might be in the same condition so new is probably best for this.

 

[Glassman]

If you go to Ford then they will probably tell you that you need to buy the whole radiator.

I had a broken mirror and they wanted me to buy a whole new wingmirror just for the glass! B'stards!

I suppose at least if you do decide to buy a new radiator that should cure the problem.

 

[mundo]

Yeah, that's what I'm afraid of. The garage that I take the car to has got a good reputation and I think they've carried out the pressure testing correctly so that would mean that I'd still have this problem even with a new radiator though!

Bit of a mystery this one and I really want to get to the bottom of it.

If I unscrew this radiator cap (when I find it) then this will drain the system (correct?) but how many litres of antifreeze/water are in there, just so I know how big a bucket to put under there. Because to even inspect the condition of the radiator cap I'm going to have to drain the system.

Thanks for you help with this guys.

 

[Glassman]

I think there's only about 3-4 litres or so. I use a plastic sink basin when I drain mine.

Have you checked that the leak isn't actually coming from somewhere else? It could be that the leak is coming from near the engine somwhere (?) and running down one of the hoses to where the radiator is. Could just be a faulty hose or a loose jubilee clip somewhere?

One trick is to wait until the engine bay is completely dry. Then get some baby powder and cover the coolant hoses with it so that they are white. Drive around for a bit and then check for any watermarks on the hoses. The baby powder should show up any watermarks and hopefully pinpoint where the leak is coming from. Obviously, you need a very dry day to do this.

 

[keyplayer]

Slow down! The cap I am talking about is on the coolant reservoir - the one I assume you've been removing to top fluid up. The principle is thus :-

The boiling point of the coolant is raised above 100 degrees by pressurising it, but overheating would result in excessive pressure which would do major damage. So within the cap is a spring loaded valve to compensate for this. At a certain pressure this will open and release pressure. This is where the steam comes from when one witnesses a boiling engine. Now if this spring has weakened, correct pressure will not be maintained and fluid loss will result. A visual inspection of the cap is unlikely to diagnose fault, you just need to try a different one.

There's no need to drain your radiator. Glassmans baby powder idea is worth a try. A pessimist might also suspect a leaking head gasket or cracked cylinder head.

And I don't want to state the obvious, but you're not overfilling reservoir are you???

 

[Glassman]

He did say that the coolant was on the floor under the radiator though.
You're right about the resevoir cap leaking but normally you can see the steam coming from under the bonnet as the water is under a lot of pressure.

 

[mundo]

No, I'm not overfilling the reservoir and have checked the rubber hose and clips and they appear to be fine. The leak definitely drips on the ground from underneath the radiator although I need to try the baby powder thing to see exactly where it's coming from as I haven't been able to pinpoint this yet, although god knows when we are going to get a dry day this summer!

leaking head gasket or cracked cylinder head

I hope not, although I'm suspecting the same thing!

 

[mundo]

I've found the drainage screw that you undo with a 1p coin, thanks guys. Looks OK to me and I don't think it is leaking from here so I have ordered a new expansion tank cap as it's worth replacing that as a process or elimination.

The radiator doesn't leak at a continual amount. Some days it doesn't leak at all and then other days it drops a few centimetres in the expansion tank so would this point towards anything...possible the cap that I am replacing?

 

[chapmanbilly]

Does the radiator or expansion have an overflow hose fitted to it. If it does then this will most likely be directed towards the ground. I once had the same problem with a BMW and couldn't figure it out I stood over the car waiting for it to happen and this is where it was coming from. The end result was the head gasket was bust, the system was pressurising and the water was being forced back into the expansion tank, the tank overfills and the water finds tis way to the overflow. Another thing you could try is run the engine to normal operating temp then feel the hoses. If they're rock hard that's usually a sign the head gasket is leaking and causing the system to over pressurise.

 

[mundo]

It's all pointing towards the head gasket!