Coolant Help!

[philwhite]

I checked the coolant this morning as I do every time I drive the car, I do this by ensuring the coolant is visible in the neck of the, usually it is or if it isn’t it only takes a cap full to bring it back into view. But this morning was different, it wasn’t visible, so I tried topping it up as normal but it just kept disappearing down the neck, I’ve added about a pint or so and it’s still not visible. So now I’m panicking badly, have I lost a tip or water seal failure perhaps? I checked the dipstick on the overflow tank and it appears full (It’s quite hard to read). Please someone tell me this is not rebuild time? Is there anything else I can check? I could see no signs of a leak?
 
The car is only 10,000 into a 5k rebuild and has shown no signs of throwing a tip, it starts hot or cold every time.
 
The cars due in the garage next week so I may get towed down there earlier (Don’t want to risk starting it).

[ajas123]

One possibility is the cap on the AST. It allows coolant expansion to the overflow bottle, but also allows flow back. Could be the cap is old and starting to fail, and only allowing fluid out to the overflow, but not back when the engine is cooling? Try a new cap. That\'s not to say you don\'t have a more serious problem, but it is a simple place to start.

[Jovic82]

the over flow tank should not be full i dont think, generally only ever about half iirc so may be down to a faulty cap - you may have even reduced its sealing power by the repeated removal.

[philwhite]

you may have even reduced its sealing power by the repeated removal.

This is what I\'m thinking, as I check it a couple of times a week.
 
I\'m going to check the caps tonight and perform the chapangne test.
 
I\'m really praying its not water seal failure, fingers crossed its not, the car has exhibited no signs and starts first time hot or cold. Hopfully is just one of the caps or an air lock perhaps.

[philwhite]

Okay, an update, got home at 5.30 and filled the cooling system with 3/4 distilled water and 1/4 antifreeze. Left it an hour while I had dinner and rechecked, levels all fine. Checked both the coolant cap and the AST cap and they both appear in good condition with no corrosion to the rubber seals (AST is correct 0.9 bar). Also checked pipes, not sign of anything loose or broken.
 

Started the engine (which started immediately) with the centre coolant cap off and there were no bubbles (yay!), small amount of white smoke from the exhaust but was clear within 2 minutes. So then went for an 8 mile drive, temp gauge did not move from the quarter to nine position once warm. Got back home and checked under the bonnet once I had stopped the engine, no gurgling and no sign of any coolant coming out of the over flow tank (although a bit hard to tell with the rain
 
So where did my coolant go? All seems very odd. Anything else I can check? I will recheck the levels when the car has cooled enough.

[ianelvar]

I\'ve had this happen on mine. Was a leak on the small hoses under the throttle body. Get a garage to do a pressure test on it while cold. 10psi or so is fine, and have a good feel around for anywhere that feels wet. Give all the hoses you can get to a good wiggle and keep an eye on the gauge. Should be nothing to worry about, but worth checking out properly.
Trying to find a leak like that while warm is worse than useless, added to the danger of burning yourself with hot coolant or engine. HTH, let us know how you get on

[kbareham]

Sounds similar to mine too. I had a very small leak in the coolant hose on the rear plate. I think that what was happening was that as the engine warmed up, the leak did not let much coolant past, so coolant was pushed out to the expansion bottle. Then when it cooled, air was pulled back into the engine through the slight leak instead of pulling back from the expansion bottle, leaving the expansion bottle too full. Water doesn\'t get through small holes as easily as air. So after a few warm up/cooldown cycles, the coolant would drop in the engine, but overflow in the expansion tank.

I changed the hose and it was fine for the next 18 months, barely ever needing a top up.

Keith