Wierd! 'banging' cooling system!

[birdo]

Another cooling oddity - just started in the last few weeks.

When the temp guage gets up to the point at which the fans usually cut in (80 deg initially) I get what can only be described as a sequence of loud clicking / banging noises , which seem to come from the fan region (although it's difficult to locate), almost as if the fans are going on and off in a split second. The banging is so severe it can be felt through the pedals when sat at lights.

The cooling system is generally working, i.e. once the temp gets up to 90 the fans are fairly consistently on, the temp stabilises and the banging ceases. Only seems to happen at the 'borderline on' temp level.

Any ideas? Fuse/Relay problem? Otter problem? I am completely

>>> Edited by birdo on Sunday 1st June 16:09

[wolosp]

Air lock?

[birdo]

Doubtful - feels/sounds more like a 'mechanical' knocking

[ATG]

80 is well below where the fans normally cut in. Could be the guage isn't accurate, or have you got a modified fan switching arrangement?

[Big Al.]

Have you seen the other half recently?


Sorry can't help on this occasion.

[birdo]

not that I know of ATG - just had a new Rad fitted which seemed to reduce the trigger temp (?) compared to before.

My immediate concern is this knocking noise at around the same temp as when the fans start cutting in - can't put my finger on what's causing it.

[GreenV8S]

Is it possible one of the fans is physically loose, or something is touching one of the blades? If it was something fairly light it might possibly get blown clear once the fans are spinning properly?

[birdo]

I'll check it, but this is happening EVERY time i'm on the border line temperature for fan cut in - think I need to get it down the garage, just wondered if it was anything obvious!!

[ATG]

Have you tried parking the car up on the drive with the bonnet up and watching what happens as it reaches temp? From what you've described the thwack is so big you might well expect to see something happeneing.

[birdo]

Yes - with all that's going on under there it's difficult to poinpoint. Maybe easier from underneath. My current 'best guess' is that it's coming from the motor mechanism on the fans - almost as if they cut in then out quickly, resulting in a 'thud'

[wolosp]

Just had a thought...maybe one of the fans motor's bearings are shot - would explain the clatter at the cut-in time, as said before by previous contributor, best to run the car with bonnet open and watch the fans as they cut in.

Edited to say it looks like you came to the same conclusion while I was typing my reply !

>> Edited by wolosp on Monday 2nd June 14:48

[leventech]

An easier and safer way to check the fans that I would use is this. Engine off (and ideally a cold engine) Ignition on, short out the otter switch wires (paper clip will work pushed up the connectors) and listen to/feel for vibration/knock when the fans cut in and out as you make and break the connection. Only a simple test but will confirm or not looses fans bearings etc.

Simon

[birdo]

Sounds like a plan! Thanks for all your thoughts - I will investigate asap and let you know what it was.

Just hope it will survive the Team Proactive Track Day at Mallory Park tomorrow - anyone else here going?

[Big Al.]

If you want to listen for shot bearing whilst the engine is running, use a screw driver with a long blade hold the blade against the motor or plastic housing, now rest the handle of the screwdriver ONTO your ear closing the opening of the ear.

WARNING I am not advocating pushing anything INTO your ear. Press the handle of the screwdriver AGAINST the ear to listen.

The screwdriver will amplify the sound along the blade.
This will allow you to hear (with practice) any anomalies, even with a V8 running.

FWIW you say it’s only on fan start up and then stops?
Could it be something lose that gets blown out of the way of the blades when the fans up to speed?

[birdo]

No, if I then get to have a blast (bit diff. in Birmingham City Centre) and bring the temp down into the 70's it'll do the same thing next time it works back up to the 80's

[david beer]

There is a kind of bang as the fans cut in, they do take around 30-35 amps on start up! If the otter is about ready to give up, it will cut in and out quickly, mine will even now if i revert back to it for testing.

[birdo]

That could be the issue - went on a track day yesterday and had serious problems with overheating - at one point the temp got over 100, steam explosion out of the expansion tank, NO fans. Is the only way to test for a faulty switch to replace it?

[spend]

IMO - YES, replace it, test the old one & if lucky you have a spare.

Test with the kettle, thermometer & a meter.

Dave