Air coming out of oil filler cap?

[MElliottUK]

Please excuse my lack of engine knowledge.

I have a alot of air in my cooling system which leads me to believe its head gasket failure. Someone suggested (when cold) to put my hand over the radiator filler to see if there was any air pressure building up. There was not, all seems fine.

Next i decided to take the oil cap off when the engine was running. There is a lot of noise and considerable air coming out of the where the cap would be (this is the oil cap, not the radiator cap). Is that normal or could this be the cause of my air in my cooling system?

On the head gasket idea, the engine does not overheat, and there is no majo but lots of air going through the heater matrix.

Any help is much appreciated.

[ylee coyote]

souds as if you have "blow by" ...exhaust gas blowing by the piston rings and pressurising the crankcase

sounds like a engine rebuild coming up....

[MElliottUK]

What will happen if i leave it as the car is not worth a huge amount, I plan to trade it in (if i can) but i need it so i dont want it to go bang before then.

If i do have piston blow by, would that result in air in my cooling system?

Thanks

Edited by MElliottUK on Monday 9th April 17:41

[GreenV8S]

It's perfectly normal for engines to produce blow-by, but excessive blow-by is one sign of a worn engine. However, it's normal practice for modern engines to be installed with a breather system that connects the crank case to the air intake so that the breather gases are sucked back into the engine and burnt, and on these engines if you release the oil filler cap while the engine is idling you should find air being sucked in rather than blown out.

The cooling system should pressurise itself in normal operation, and pressure in the cooling system doesn't necessarily mean you've blown a gasket. If the head gasket is blowing badly into the cooling system you will find very obvious bubbles and steam coming out of the water filler cap when you rev the engine. For a smaller leak you'll get trac amounts of exhaust gas which can be detected with a block tester but may not be obvious to the naked eye. If the head gasket has gone you may also find oil emulsion in the coolant, if you find this then you definitely have a problem.

[steve_d]

All engines have some blow by but you may also just be mistaking pulses of air which are created each time a piston goes down. If the engine is oldish then there will be blow by and it will continue until you rebuild the engine. On its own it is not reason to think engine failure is imminent.

You can buy a tester for the presence of exhaust gases in the water system. This sniffs the air in the water filler neck and changes the colour of a liquid in the tester. This will prove if the HG has failed to the water jacket but not if it has failed cylinder to cylinder.

If funds are short then all you can do is carry on driving it until something more dramatic happens. Apart from driving it a little more gently there are no service or remedial measures you can take to prevent it getting worse.

Steve

[rich 36]

I'd heard RESTORE




is a good bet

[ylee coyote]

the way to tell for sure is to do a compression test
quick and easy and cheap
this will tell you if you have a prob or not

[MElliottUK]

I got a ex mechanic to look at it today, he said the blow-by is above normal, but not massively bad. (engine has done 70,000 motorway miles, 1.2 8v engine so its been sustaining semi high revs to keep me at 80mph)

As for the air in the cooling systems, i don't know ive bled it lots of time and it just comes back. No majo in cap, oil looks clean, no bubbles in the radiator.

If i open the bleed screw on the right hand side of the radiator, lots of white water comes out (water mixed with bubbles, giving it a small rev will help shift some more as will knocking the radiator about). So seems like gasket but no apparent signs other that the bubbles, im just not sure where they maybe coming from.

I guess its a trip to a mechanic. The mechanic that looked at this problem ages ago suggested that it might be a blocked vent valve that would vent and air back into the reservoir (bit you put the water in). I thought that seemed far fetched at the time as it would have meant a new radiator that i wasn't sure was going to fix the problem.

Fiats, dont think i will ever get another.

Edited by MElliottUK on Monday 9th April 20:05

[Trooper2]

Run the engine with the coolant reservoir and/or radiator cap off and look inside. If the headgasket is blown to an adjacent waterjacket in the head/block you will get fairly large bubbles in there and you might even be able to smell engine exhaust. Also take a wiff of your exhaust, if it smells like coolant that's another clue.