dreaded bubbles in the coolant

Savman

hey I've a 96 diesel mondeo with this recent problem, does this always mean head gasket is fooked? and anyone have a realistic guess as to what it costs to fix?

or could it be something else...

AMurphy

does it tend to overheat as well?.

The traditional way to tell if these bubbles are steam of engine gas is pull the gasses through a mix of lime and water, Co2 in the gasses will turn the test mixture milky. Try it with glass of water + lime using your breath and a straw.

BrianD3

There is a device to test for exhaust gases in coolant. I'd enquire at a garage and get them to do the test (assuming they have the right equipment) But even if you have a good sniff at the expansion tank you'll probably be able to smell exhaust gases if they are getting in there through a blown HG.

As for other causes if you had a coolant leak you might get air in the system which could produce bubbles although I have never witnessed this. Also if your system is not holding pressure (eg due to a faulty cap) the boiling point of the coolant will be lowered and you might see coolant boiling and bubbling in the expansion tank.

Savman

first thing I did was check for odd smells, nothing noticable...

has never overheated engine always been at normal temp. It's just "Head Gasket" is the first thing everyone says when you mention bubbles in the tank, in the case that this is tru would anyone know what kinda € I'd be looking at (hypothetically speaking ...;) )

stratos

It would be generaly unusual for a diesel engine to blow a head gasket. The pressures and temperatures involved are far greater than a petrol engine, so they are built stronger.

Bubbles in the coolant can be caused by cavitation from the water pump or other things like cylinder wall detonation shock. ( a normal process).

A loss of coolant would be seen, and probably oily film / deposit on the coolant, and a lack of power eventually if it were the head gasket.

Interceptor

My 96 Mondeo diesel blew its head gasket - I noticed water dripping from the expansion tank and when I opened it the pressure of bubbles forced a pint of coolant out of it. When I checked it I found the thermostat had failed closed and there was no water going to the radiator, causing the engine to overheat. Does the heater in the car work properly? It may work poorly due to airlock and this might also indicate a head gasket problem.

'cptr

Savman

I guess I'm hoping its something else, maybe something small...

There doesn't seem to be coolant loss, I can only guess that the temp guage is working ok, when its cold it displays cold and when its warm it rises to "Normal"

It was kinda out of the blue, I'd think I would notice something out of the ordinary like overheating, even if it was subtle...

I've had a lot of starting problems but dunno if that'd affect this kinda thing (starter motor, glow plugs, ignition switch, y'know typical ford diesel winter starts:rolleyes: )

cheers all, any more thoughts welcome

Savman

ok me again!

Studied the coolant tank with the engine running, it actually looks like the bubbles are coming from the tank itself, it looks like some of the coolant is returning thru a hose and creating what looks like a mini-waterfall (for want of a better phrase:o)

Sorry I don't know the right terminology I'm trying to educate meself in the science of cars but it looks as though there may not be air getting in as it looked on first glance. There's defo no coolant loss, anyone have any ideas on what this could be???

crosstownk

The tank is an expansion tank. As coolant in the system expands, excess coolant is fed back (under pressure) to the expansion tank. As this coolant is very hot (nearly boiling) bubbles will be seen.
When the coolant in the engine reduces in temperature, coolant from the expansion tank is drawn back into the engine. And the cycle goes on....
Therefore, the bubbles are normal.

Savman

thank you