Air Lock Symptoms??

[HeyAndy]

Can anyone tell me what the symptoms are for an air lock and how to cure it pleeeze?

Whilst driving at speed with or without the rad fan being on, the car's temp goes into the red. The header tank though not boiling over, is dumping water into the overflow tank when the car's stationary.

I'm suspecting the thermostat could be faulty as the car should cool down when travelling at speed even when the fan is off but its not happening. There's no aparent loss of coolant and the oil is not contaminated. If the thermostat was faulty would it explain why the header tank is dumping its water?

Both rad hoses are also hot especially the lower hose which should be cooler than the top hose if everything is working normally.

My car's an 89 350i? Any help is appreciated

Thanks

Andy C

[19560]

Sounnds like it could be a split head gasket or blocked radiator core. Check the rad first with a flow test, its simpler and easier.

[Brm Brm]

Sounds very head Gasket-ish to me - cylinder to water passage leak. An air lock will usually cause the temp guage to rise very quickly into the red, stay there for a few seconds then drop to normal just as quickly. Of course a knackered head gasket can cause air locks.......

[jmorgan]

Flushed rad sorted that out with a local owner. But shouldn't be taken as the cure in your case. He found no end of crud in the rad.

Also the above know more than me, just relating a fix that worked for him.

[briantvr350i]

Andy,

the symptoms you describe are exactly right for an air-lock...

OK, have you filled the radiator EXACTLY as "the bible"?

The critical bit I've found through experience, is to fill the system through the expansion tank until the coolant is level with the plastic prong visible through the filler hole. Then put the cap on (the one with the spring!)

Start the engine and allow to idle, filling coolant as required through the cap on the swan neck. Keep checking the temperature of the coolant in the swan neck, at some stage the thermostat will open and the coolant will flow round the system. More than likely overflowing at the swan neck, the cap can now be put on.

Continue watching the engine temperature which should rise, the fan(s) will cut in controlling the temperature before it hits the RED.

There may be some loss of coolant during the phase.... Don't worry UNLESS this happens every time the car is fully warmed up.... In which case start looking for another cause.

The biggest secret with wedge cooling is to make sure that no air is trapped in the hose between the thermostat housing and the swan neck cap. This can be achived by making sure that the hose out of the thermostat housing is as low as possible so that the top of the hose, and the top of the swan neck, is lower (when the car is level) than the level of the water in the expansion tank.

This is difficult to explain, but is very easy to show on a car. By the way, it's much easier to do all the above with the bonnet off.

You will also notice that I have not mentioned temperature in degrees, the gauges are not really accurate enough and cars very considerably. The temperature should be stable while driving, will rise when you stop (usually quite quickly) but the fan(s) will just about cope with the with British summer and control the temperature. The engine will cool rapidly once you hit open road again.

Regards,

Brian (and a RED 350i)

[19560]

Brian, he's got no flow or next to no flow through the rad yet both hoses are hot. I think that an air lock is a symptom of the main problem and not the cause. A blocked rad could cause an air lock and if unlucky lead to a head gasket failure or even worse.

[briantvr350i]

Yes Jonathan it could be a blocked rad, but let's look at the simple cures first...

The air lock is most likely to be between the thermostat housing and the swan neck cap. Any air here reduces the flow. I had this on my 350 after I changed the hose to a silicon one and didn't initially cut enough off the end which fits the termostat housing. And during this period both radiator hoses were hot....

If Andy changes the thermostat, use Jooles (Joospeed) tip and drill a couple of small holes to allow the air trapped behind it to escape (although I prefer just a couple of smaller holes,1/16th. inch or so, than Jooles) otherwise it takes an age to warm in the winter. Obviously position the stat so these are at the top!

I wonder if Andy has any more information? has he just got the car or has something been done before the problem started? Has the car ever run cool?

Regards,

Brian (and a RED 350)

[19560]

Fair enough. How are you getting on Andy?

[HeyAndy]

Hey guys - thanks for the replies. I'm going to run with Brian's tip on filling up the coolant.

I've had a wedge before an S1 so I'm familiar with the airlock problems, the S2 has a different set up altogether and thats why I'm confused but both cars have showed the same air lock symptoms.

I know its definitely not a gasket problem as the temp will get hot and setle back well below 90c with the fan on when driving now though it will creep up again with the fan still going with no sign of overheating (the car hasn't boiled up at all).

What i've been doing is to fill the header tank and swan neck, putting the cap back on the header and filling up the swan neck - but not waiting for the thermo to open. I'll try that next.

I live in London so it would be cool if we could meet up so I can get a demo from someone who knows! I've also got some other niggles that need an opinuion too.

I'll keep you posted.

Andy