Technical do you have air bubbles in your reservoir?

[eolonano]

Hello guys,

I'm dealing with a problem that I think is a generical tech question, so I have posted it here:
https://www.fiatforum.com/tech-talk/460696-air-bubbles-reservoir-head-gasket-failure.html

the car is a Multipla CNG, but the seller's mechanic has assured me that it's the same on petrol models. He says: when you rev your engine and a lot of bubbles appears inside the reservoir (they flow from bottom to top), that's perfectly normal!!

Can you check this on your car for me, please? :worship::worship:
I think the mechanic is bull****ting me.... but I can be wrong

 

[martyc5674]

I think there was always a few in mine... I sold it though so can’t check for you.

 

[eolonano]

Thanks anyway, Marty.

I just want to add that the bubbles are really a LOT.

It's something like when you agitate a bottle of sparkling water, ad then you open the cap: the bubbles coming up in the reservoir are a lot more, but smaller.

Another thought was that perhaps the spinning of the water pump was causing it, but no, there is too much longer hose from the bottom of the reservoir to the water pump: in between there is also the thermostat.....
I mean: if they are normal bubbles, it's easy for them to go with the flow, and come out of the return hose on the top of the reservoir...

Anyone else still has a multipla and can check for a lot of air bubbles when engine is warm (so the thermostat is open) and revving?
Thanks

 

[martyc5674]

Have you tried bleeding it... could be a lot of air in the system... two bleed nipples on the top of the rad either side... and one to the right of the engine heading towards the back in the top of s hoses. Need to be bled when stat is open for best results IIRC. I’d bleed open and closed with the reservoir open.

 

[eolonano]

Thanks Marty, on my car I always bleed any air from the system.

Here, the problem is that the car is not mine, I would like to buy it...
So, I prefer to avoid touching the car because the seller it's not an expert and I don't have a badge that says that I'm a qualified mechanic.

On the other hand his mechanics are, on my opinion, incompetent: they keep saying "it's normal!"

But I don't think it's normal. I even suggested to the mechanic (when he says to me that the air is expelled from the system by the return hose) to bleed using the little cap on the radiator and the other cap usually in the higher spot of the engine (as you said).....

To be honest, I think that the bleeding caps are there to prevent airlocks, meaning avoid trapped air that can reduce the cooling efficiency. If that air could go around as I see it, coming up the way it does, bleeding would be actually be automatic. the air will stay in the reservoir, and the level of coolant drops down a little.

Instead, every time you rev, huge quantity of bubbles are produced; so, every time has to be "new air" injected into the system; if not, the level of the coolant has to drop down, taking the place of the displaced air...

I'm not sure of my English...so I hope that what I'm saying is understandable enough....

 

[martyc5674]

Yeah I understand you alright and it makes sense what you say... but I do think there were some bubbles in mine... just a small few though, and the head gasket was fine.

 

[eolonano]

@ marty
your air bubbles were perfectly still on the surface of the water, or they were coming up from the bottom hose of the reservoir during the revvings, and then disappear?

Sorry if I ask again, just to be sure....

 

[martyc5674]

I definitely remember them coming from the bottom.... just a single stream of them though.

 

[g8rpi]

I definitely remember them coming from the bottom.... just a single stream of them though.

This is NOT normal. Either there is a lot of air in the system which is bad because it can cause hot spots, or the head gasket is leaking. You need to either have a mechanic who you trust check the car or get a written guarantee from the seller that you can return the car for a full refund if there turns out to be a problem assuming that it is a business seller.
There are various ways to check for head gasket leaks. One is a tester that connects to the header tank nd has a liquikd th changes colour if combustion gases bubble through it.


Robert G8RPI.

 

[martyc5674]

Sold it a few months ago... this is how I remember it, possibly that memory is from after changing water pump or stat tho... I do remember some bubbles drove really well sold with nearly 200k on it

 

[eolonano]

thanks g8rpi,

In fact, a few days ago I've ordered cool: from the sunny England ) the liquid to test for CO2 presence in the water.....

I have somewhat discarded the possibility of the same amount of air running around in the system for this reason:

If every time I rev the engine I see a lot of bubbles coming up in the reservoir, it means that in a way, the system is bleeding itself: bubbles leave their place inside the hoses and go in the reservoir, so that the liquid in the reservoir drop down into the hoses.
So, in this case, after a few revs, the phenomenon has to diminish its intensity: less and less bubbles every time I rev the engine.

In my case, the massive mini-bubbling is always the same, with no regard how many time I rev...:bang::bang:

I'm thinking to avoid that car (or at least check it thoroughly with the liquid tester); but I want to collect more information I can from you guys before attempting to buy another one ( what if I find another car with bubbles ?)

By the way, the mechanic keep repeating that it can't be a head gasket leak because the car runs smooth, the engine is not overheating, and the rubber hoses haven't become stiff (because the hot gases cook them) ...... :shrug::shrug:

 

[wiltshire]

If the water level is not dropping then the bubbles could be of steam, steam bubbles can be produced by cavitation in the water pump. The steam condenses back to water so that there is no change in level despite the 'air bubbles', if air really is entering then water must be leaving.

 

[g8rpi]

If the water level is not dropping then the bubbles could be of steam, steam bubbles can be produced by cavitation in the water pump. The steam condenses back to water so that there is no change in level despite the 'air bubbles', if air really is entering then water must be leaving.

Not true, if there is a head gasket issue the gasses from the cylinder(s) is being forced into the cooling system and escaping via the header tank and pressure relief cap. no loss of coolant involved. There should be no boiling in the cooling system. The system is pressurised to stop boiling. Even if there is localised boiling in the head area this would re-condense long before it reached the header tank. Likewise any trapped air would eventualy clear out of the system if it is bubbling into the header tank. This leaves two possibilities, the header tank is leaking causing loss of pressure and boiling in the engine or there is a head gasket leak. As the car does not seem to be loosing coolant aleak is unlikely leaving a head gsket problem as the most likley issue.


Robert G8RPI.

 

[eolonano]

CAVITATION

I've thought of cavitation, but it doesn't convince me because of the way the bubbles are coming up:
Cavitation works like this:


as you can see the steam bubbles stay on the same spot or they tend to move towards the water pump that is creating a depression.

In the Multipla I saw, the bubbles come up in the reservoir from bottom to top rapidly, in the same way you can watch when you open a bottle of sparkling water.

On multipla, it seems that the flow goes from the reservoir to the thermostat, and then, inside the engine, it goes to the water pump: if there is cavitation, it has to be between the thermostat and the water pump; again, it seems that cavitation damage are found only in cars where the pump goes up 7000/8000 rpm (because of the engine or because the pump is overdriven: does multipla have a WP sprocket bigger than the engine sprocket? I've tested at around 5000 rpm).

COMBUSTION LEAK

I've thought of a pressure leak in the system (perhaps a bad cap valve, because I saw a some little pink stains from coolant around the cap),

but the problem is that the air bubbles come up also when you rev just after starting the vehicle. So there is no time for the water to become hot and build up pressure.
And the stains can be caused by the cap that is doing is job releasing a lot of pressure caused by the head gasket leak..

I can't explain why I can see the bubbles when the engine is cold; the thermostat has to be closed, and so the circulation is inside the engine only...... can be a thermostat stuck open? or the pressure of gases can open the thermostat valve?

It's a pity that I didn't check for pressure buildup using a hand on the opened reservoir......