Coolant drop/pressure! ?

Hi I have a TF 2004 1.8 and have noticed that if I check the coolant level in the expansion tank after a good run the coolant is way below the minimum level. However, when the engine cools down (cold) the coolant level is back to normal!

Is this normal?

Robert

No, it should sit at the same level. My guess is that it is pressurising due to the header tank cap not venting properly, as the cap is a service item I would change it BUT make sure you get a genuine one and not a copy.

Thanks talkingcars

Have a new spare cap so put that on to see if it makes a difference. Will take it out for a drive tomorrow to check.

Thanks again for your input.

Robert

Hi had two brand new pressure caps, one on the car, one spare.

Cleaned the one on the car to ensure that the spring was working correctly and replaced, as this has sat for 5 months while Sorned Still fluid pressure drops. Fitted second cap fluid still drops but not as bad.

Any other other suggestions?

Have ordered three new ones!

Robert

If you are not losing coolant then maybe you should give the system a good bleed, maybe you have some air pockets when the coolant pressurizes then possibly the air pockets compress and the coolant fills the space.

Sundance

Hi Sundace

Did that yesterday and also to be on the safe side this morning before the run. Being a little paranoid have checked the oil for mayo and coolant for oil. None. I know these are not definitive checks, but all ease the mind.

On a 100 mile run tomorrow. Thinking should I!

Robert

Hi. Went on my 100-mile trip. Water-light on three times. Inspected, panic, coolant down below minimum, hence light activating. Got home, new coolant caps arrive. Fitted one, and all seems ok, good twenty-mile run, no movement in the coolant level.

Thanks guys.

Robert

Similar thing happened to my 99 F the other day. The cooling system has never given me any bother in the two years I have had it, and it spends winter sorned, and off the road.
When I am home I always fire it up and let it turn over for half an hour or so until the fans kick in, but last week I did the same procedure, then turned off the ignition which was the cue for the expansion cap to vent. Coolant every where!
It was getting late; so left it until the following morning, checked what I could in the pouring down rain, but there was nothing that obvious I could see.
I refilled the coolant, put a new cap on (genuine xpart I had as a spare), and the engine idled as normal, coolant level stayed the same, temperature gauge normal.
54k on the clock and original head gasket as far as I know; so I suppose the expansion cap did its job, but why it happened I don't know, now I'm thinking have I got away with it...….
Also am I right in thinking that once the cap has vented its useless putting it back on?

In theory, there are two reasons for the cap venting. Overpressure in the system or failed cap.

If it is overpressure then a new cap will vent also. So the old cap would be reusable once you resolve the overpressure issue. Having said that I would still go with a new cap.

However, it is much more likely that the cap itself is faulty, so a new cap will sort the problem.

Thanks for the advice David. I've just had the car running for 30 minutes again with the new cap still on, and its fine; so probably a failed cap which I will bin.
What would cause "over pressure" too much coolant?

Another two ordered for spares just in case!

Overpressure would be caused by HGF. Combustion gases getting into the coolant.

Hi David
Thanks for the input just completed a 200-mile round trip after fitting new pressure cap. No problems car ran "sweet as a nut". No pressure increase or drop in fluid.

So have purchased two new caps (just in case!).

Regards
Robert