[BLiTZ]

I'm probably being paranoid, but a couple of times when I've popped the bonnet with the engine still running I've noticed small bubbles (5mm max) dancing around in the coolant tank. Not many, 2 or 3 at a time around the small hoses that feed into the tank. It's not a stream of bubbles, more like a small pocket of air that's trapped in the flow of coolant.

No my immediate thought is bubbles in coolant is bad, but it's not like the whole lot is bubbling away.

On my last car the return feed was above the water line so would pour in disapating any bubbles I guess, where on the ST the return appears to push fluid back in from below do maybe like blowing a straw into a drink it's just the pressure doing its thing?!

Has anyone else noticed this happening at all?

 

[BLiTZ]

Right, to add further paranoia, I decided to delve a little deeper, and had a look at the car this morning. First off I took the coolant cap off to check for any abnormal pressure, aside from a slight hiss when I first loosened the cap the tank didn't seem to be under pressure, nor did the coolant level change so that seems ok.

I also checked for any mayo under the coolant and oil caps and both were clear.

Then with the cap off I started the engine and let it idle, I couldn't see any obvious bubbling (what doesn't help is the baffles in the header tank that mean the level under the cap is 'protected' from the inlet pipes so any bubbles tend to collect at the other side of the tank.

Then once warmed up a bit, I asked my wife to rev the engine whilst I kept watch. There appears to be a degree of bubbling, now I don't know if this is to be expected or not, Googling would suggest you shouldn't see bubbles under any circumstance and is a sign of a head gasket failure. I took a few videos to see if anyone more knowledgeable can shed some light:

View attachment trim.F5CD945D-6D3D-4DFD-BE94-C74100298E67.MOV View attachment trim.35C79720-FB25-4DB1-8E41-4C3A853B548B.MOV View attachment trim.9AB0BB30-535D-428F-BFBC-09CE7D96AC5E.MOV View attachment trim.2BE67F59-491E-43DF-BEAF-267D89D6630E.MOV

 

[###simon###]

You will always get some bubbling as it's basically a continuously circulating water system. Even under pressure it will still happen, as long as you have no leaks and it doesn't overheat I don't think you have any issues at all.

 

[BLiTZ]

Thank you, I just scared myself a little watching vids on YouTube with bubbling cars with HGF.

Car doesn't overheat, even after a good run the coolant level is only about 8-10mm above max.

 

[BLiTZ]

Still pretty worried about this, spent all last night Googling bubbles in coolant and out of 30 or so links to various forum (covering all makes and models so not all set up the same as the ST) the general consensus is there shouldn't be any air bubbles.

Posted the vids on the ST Bookface group to try and reach out to more people and got mixed responses. I think people were getting more focused on the turbulence when the engine's revved (which I accept is the normal results of the increased flow) rather than the small air bubbles that appear then float to the side and pop.

It'd be appreciated if someone could get a video of their coolant tank once warm with a few revs to see if theirs bubble too.

 

[sme101]

Im no expert but i wouldnt worry about it imo.

You say the coolant looks pure so theres no mixing of anything.

Its not a sealed hydraulic system (half the expansion tank is air) so there will be some turbulence.

If you look through the open cap can you see bubbles coming out of the return hose while its running?

 

[Darran]

If you join the "Fiesta ST Owners" Facebook Group, there's a thread on there, just search "bubbles":

Link here: https://www.facebook.com/groups/739924502789990/search/?query=bubbles

General consensus is it's normal and nothing to worry about.

 

[BLiTZ]

Yeah the coolant looks clear. There was a tiny fleck of crud floating on the surface but that could have knocked in from the cap coming off or could be a bit of corrosion from elsewhere in the system, but the surface didn't look oily and when cold it smells the same as other coolant tanks I've sniffed over the years (to me a sort of fishy smell).

Due to the design of the tank it's hard to see the flow from the return hose as there's baffles that blank off the various parts of the tank (there's a great pic on the US forums where Mishimoto have cut the top off a standard tank and you can see that the tank is segmented into different compartments and levels)

There were no bubbles coming to the surface with the cap off from cold (I replaced the cap before revving to avoid splashes) but that could be that it wasn't up to temp.

My only hope is that it's one of those things that's normal and people only notice when they have other symptoms and do further diagnostics as unless you had a camera under the bonnet you'd never notice as it's a two man job to rev the engine and view the tank and as I say at idle there's maybe only one bubble or two just floating in there.

But like most issues, once you discover something you start to worry.

If you join the "Fiesta ST Owners" Facebook Group, there's a thread on there, just search "bubbles":

Link here: https://www.facebook.com/groups/739924502789990/search/?query=bubbles

General consensus is it's normal and nothing to worry about.

That'd be my post lol

 

[Darran]

That'd be my post lol

Small world :biggrin:

Have you checked the coolant cap?, these are known to fail:

http://www.fiestastoc.com/forums/topic/269033-coolant-and-general-faults/?p=3760881

 

[BLiTZ]

It had a new cap only a month or so ago as the o ring on the old one had come loose.