Coolant level help

[chr1s]

Hi, wondering if anyone can explain what is going on with the coolant on my FD?

Every time I start the car from cold the warning light/buzzer comes on and then goes off after about a minute of driving, this only happens when the car is cold. The level in the central filler seems to always sit about 2 inches from the top just under the small hole. Even if I top the filler up to the brim the coolant warning comes on then goes off and then next time the car is cold the level has dropped again but coolant is always visible in the filler.

The AST is full to the top, the AST is aluminium and has a nearly new cap all the hoses are tight. Today I noticed some coolant had escaped from the top of the AST although it was still full. The overflow tank is showing higher than the full mark on cold.

No champagne bubbles in the filler when the car is running.

Anyone able to give any pointers what to look for?

Thanks

[clive]

Hi Chris,

When you say some escaped from the AST, if you mean it could be coming from around the seam then it needs replacing as this is a common failure

[Arnie_O]

Clive he said its an aluminium AST so pretty unlikely.

Out of interest how did you check for bubbles in the system?
Did you simply take the cap off or stick a bottle in the kneel with the bottom cut off then fill with coolant.

From experience don\'t keep filling it to the brim as all your going to do is fill your overflow tank.

[chr1s]

The AST is aluminium so I doubt it has failed. I think perhaps I have been overfilling it as the AST is full to the brim and the overflow tank is higher than the full mark. What I don\'t understand is why the coolant warning keeps going off even when there is coolant visible in the filler? Also is it normal for the AST cap to let coolant through?

I just looked for bubbles in the filler neck and can\'t see any. Engine was rebuilt not that long ago and always starts first time.

Chris

[mikey-t]

Get it looked at properly and check EVERYThInG I had similar symptoms before my water seals let go,

[boosted]

Ast cap has no spring in it overflow cap has spring. Dont get them mixed up like I did. Does it alarm then stop once warm?  Or are you filling? Overflow tank when hot will vent to small tank behind headlight and will draw back from that when cooling down so should maintain levels.

[boosted]

Edit...The cap lifting scenario is usually after some spirited driving where the car has got pretty hot and pressure has risen to 0.9 bar to overcome the spring pressure.....you\'ve changed Ast cap have you also changed the overflow cap?

[chr1s]

My AST cap has a spring in it, the central filler cap has no spring, I can\'t mix them up because they are different sizes. The alarm always stops after about a minute driving. I haven\'t added any coolant for the past few runs and the level in the filler seems to have stayed constant about a couple of inches below the top when cold.

[Speedline Imports]

Quiet a common cause for this is the main filler cap failing.  This is the one with the Yellow arrow.  This is the only place you need to fill up from.  

The AST is the red arrow which you have replaced with a alloy replacement.

The main filler is a standard cap without a spring where as the AST does have a spring.

First thing to do is replace Main Filler Cap (Labeled YELLOW arrow)

[boosted]

Was just looking  for a diagram like above! Soz got the caps the wrong way round AGAIN!:2Confused
 
when mine was playin up i pinched 1 of an mx5 i had at the time. Neither car had never had a problem again.

[chr1s]

Thanks Martin, I did suspect the main filler cap as I have never replaced this. I will try a new one and see if it improves. I only ever fill from this location.

[Arnie_O]

Why would the main filler cap fail... There is no pressure bypass on it as that\'s dealt with at the AST.
unless your talking about the rubber seal failing and allowing coolant out of the system?