[Skov]

My 5 has decided to start p!ssing it's coolant out of the overflow on the expansion chamber.
It's not overfilled - in fact when it cools down the tank is pretty much empty (as you might expect if it's all been leaking out!)
If I lift the top off the expansion tank whilst the engine is running you can see a constant stream of air bubbles coming out of the pipe that comes from the top of the radiator.

Checked my cylinder compression - 3 of them are at 12 BAR, and the other (3rd from the front) is at about 11.4 BAR.

Is my head gasket buggered?

-------
UPDATE: It looks like it probably was a leaky head gasket. After changing it all 4 cylinders are at about 12.5 BAR, and I'm no longer losing coolant

 

[Midnight Racer]

I'm no expert but have you thought about it being a faulty rad cap?

always worth looking at the simpler things first!

 

[Skov]

I'm no expert but have you thought about it being a faulty rad cap?

always worth looking at the simpler things first!

I don't think so - I replaced it with a new genuine mazda one only 4 or 5 months ago.

 

[stigatronix]

it sounds like youve got the simptoms of a head gasket failure. combustion gases are presureising your coolant system . a "block test" were a colour indicater is used to sniff your radiator would be a conclusive. if combustion gases,are present in the coolant the blue fluid goes green if its subtle or yellow if its blatent. check if this is a test/service your local garages can undertake. should cost no more than ?20,then youd know what your up against.

 

[Skov]

I decided to just go ahead and start stripping it down this morning. Hope it is the head gasket now, or I'm going to feel rather foolish!
Judging by the coolant it looks like a previous owner tried to fix it with that horrible k-seal stuff or something similar. I guess it worked for a while...

Is it worth doing any other work whilst I've got the head off?
The car's done about 85k miles if that makes any difference.

Thanks.

 

[miles]

It's your rad cap, buy a proper one from Mazda. Patent ones don't work.

 

[indykid]

It's your rad cap, buy a proper one from Mazda. Pattern ones don't work.

mine's fine....but if it makes you feel better, give mazda your money

the op said they put a genuine one on 4 or 5 months ago.
tom

 

[Carlos Fandango]

I decided to just go ahead and start stripping it down this morning. Hope it is the head gasket now, or I'm going to feel rather foolish!
Judging by the coolant it looks like a previous owner tried to fix it with that horrible k-seal stuff or something similar. I guess it worked for a while...

Is it worth doing any other work whilst I've got the head off?
The car's done about 85k miles if that makes any difference.

Thanks.

Skov

whilst you've got the head off I'd consider lapping the valves just to make sure they are gas tight again and maybe replacing the valve stem oil seals as a precaution as they do go off with age/mileage.

You might also want to consider port matching both the inlet and exhaust ports but if you do that you really need to strip the head right down so you can make sure it's properly clean afterwards - but you'll have the cams and valves out any way to lap the valves.

 

[Skov]

I decided to just go ahead and start stripping it down this morning. Hope it is the head gasket now, or I'm going to feel rather foolish!
Judging by the coolant it looks like a previous owner tried to fix it with that horrible k-seal stuff or something similar. I guess it worked for a while...

Is it worth doing any other work whilst I've got the head off?
The car's done about 85k miles if that makes any difference.

Thanks.

Skov

whilst you've got the head off I'd consider lapping the valves just to make sure they are gas tight again and maybe replacing the valve stem oil seals as a precaution as they do go off with age/mileage.

You might also want to consider port matching both the inlet and exhaust ports but if you do that you really need to strip the head right down so you can make sure it's properly clean afterwards - but you'll have the cams and valves out any way to lap the valves.
[/quote]

I was considering lapping the vavles, not sure if I will or not now as mx5parts wants ?107 for a set of valve seals!!!

Is there much to be gained from port matching?

 

[Carlos Fandango]

I decided to just go ahead and start stripping it down this morning. Hope it is the head gasket now, or I'm going to feel rather foolish!
Judging by the coolant it looks like a previous owner tried to fix it with that horrible k-seal stuff or something similar. I guess it worked for a while...

Is it worth doing any other work whilst I've got the head off?
The car's done about 85k miles if that makes any difference.

Thanks.

Skov

whilst you've got the head off I'd consider lapping the valves just to make sure they are gas tight again and maybe replacing the valve stem oil seals as a precaution as they do go off with age/mileage.

You might also want to consider port matching both the inlet and exhaust ports but if you do that you really need to strip the head right down so you can make sure it's properly clean afterwards - but you'll have the cams and valves out any way to lap the valves.
[/quote]

I was considering lapping the vavles, not sure if I will or not now as mx5parts wants £107 for a set of valve seals!!!

Is there much to be gained from port matching?
[/quote]
Every little helps, especially if you're not running FI.

I bought the head gasket set from Scimitar which included the valve stem seals and a few other bits for a head refresh - currently £53.97 plus delivery.

Or a set of seals on ebay now for £21.75 + £1.20 postage.