Mysterious Sound On Cold Start

[Trozzle]

ok guys, this sound has become apparent since the last oil change (now on roughly 6000kms thanks to Canberra - Melbourne return, doing again this wednesday), or a stack of suspension/steering work I had done at the same time, and only ever happens on a cold engine though it lives outside so is much more likely to do it when I start it in the morning after freezing overnight.

The only thing I can relate the sound to would be the sound you make when sucking the last bit out of a milkshake or thickshake through a straw - you know, the sound you're embarrassed to make sometimes coz it's loud. It appears to be coming from under the front of the car, hence engine.

It is able to be "recreated" as I reverse down my driveway, as it's relatively steep and places the car on quite an incline. Has only done it on one occasion before I've even moved the car, which was this morning, hence why I'm writing this. As I'm reversing down the driveway, when I touch the brakes or bring the car to a stop, this is when the sound occurs. It's as though the car stopping causes whatever is making this sound to move backward through momentum, and do it's thing.

I don't understand the insides of the sump, and how oil pickups etc work, but from an ignorant point of view I have suggested something like the oil moving to the back of the sump as I brake on my driveway....but this has been dismissed (not to mention why does it only happen on a cold engine?)

Whatever's causing this can also be felt through the firewall via my foot on the clutch, so something is definitely vibrating or something.

Mods are only 3.5" turbo back, FMIC, bleed valve @11psi...suspension is bushes bushes bushes, ISC coilovers, rack mounts, front+rear upper camber arms, rear traction, and HICAS lock...though I don't think any of this will be the culprit...

/end wall of text, thanks guys.

[The Dan]

Bleed your cooling system and make sure the heater is turned on when you do so and try to do it on a hill so the air moves towards the front of the engine.

Sounds like the water is moving about. It's the sound it will make when air is travelling through the system.

[Trozzle]

yes, it definitely sounds like air through a liquid system, though what do you mean by "cooling" system? As in, water/radiator etc etc, or aircon?

And if you're correct, this wouldn't be detrimental at all would it? Not causing damage that is

[Spurdo]

generally wont have harmed your system, as long as engine temps havent been out of control it will be fine.

cooling system refers to water/radiator. when you bleed/flush your cooling system you need to have the heater controls set to hot and turned on so that the cooling system is fully open and you dont trap any air in the heating system. the best way i find to absolutely guarantee no air in the system is to have the radiator cap off, pull off one of the heater hoses on the firewall and place your thumb over the end, then shove a running garden hose into the fitting on the firewall. when the air bubbles stop coming out the top of the radiator, system is bled. should take up to 15secs or so (dont take forever doing this or eventually your anti-freeze will become plain water) quickly remove garden hose and re-attach the heater hose to the fitting on the firewall and replace radiator cap.

this method is yet to fail me.

Edited June 28, 2010 by jonboy

[joeyjoejoejuniorshabadoo]

on the rb25 there is also a little screw you remove near the front of the valley.... i'm guessing 26's are the same?

[Trozzle]

ah ok, makes sense now since it's going into the shop on wednesday for brake machining/general service, I'll get them to do that too.

Aftermarket gauge has never red more than 90 deg, and will sit on 80 - 85 during normal operation, so overheat definitely hasn't occurred

Thanks for the input guys, much appreciated! Will update with results later in the week for future reference

[Granthem]

I have the 'straw noise'. I believe mine is air in my power steering rack.

[Trozzle]

does it piss off once the engine has warmed up for a couple of minutes?

[Granthem]

Certainly does! By the time I'm a few traffic lights down the road its gone. I have noticed a leak from my power steering rack, and I believe its air getting into the power steering system.

[Trozzle]

will have to have that looked at too....I've noticed my fluid was low a while back, though it hasn't gone down since I topped it up....

Dropping it off at workshop tonight so they can leave it outside over night and start it when the thing is frozen in the morning, hopefully it makes the same noises and they can work it out.

OH just realised though...it's making a sound before I even touch the wheel, but the main sound is after I've turned it (not directly after, but the steering has moved before I ever notice it)...still reckon the rack is possible?

[Granthem]

Mine makes the noise before turning the steering wheel aswell. The power steering pump is driven by a pully off the engine, so if your engine is pumping, so is the power steering pump (whether or not you are turning the wheel or not).

* thats my take on it, someone correct me if I'm wrong.

[Trozzle]

the pump is turning yes, but the rack itself doesn't receive anything until you turn the wheel....well at least that MY take on it lol.

Either way, at least you've given me something else to suggest when I drop it off...some small part of me wants it to be a big bad monster so I can get the thing built lol...oh I don't know

[Randon_I_Am]

BAHAHA, looking for an excuse for a rebuild eh?

just up the boost and drive it like a maniac till the "noise" does become a big bad monster

[Granthem]

Yeh my thought was it might be air in the pump causting cavitation, hence the milkshake gurgle noise...

[Trozzle]

Yeah air in liquid (be it water, power steering pump....even oil, though that's VERY unlikely) seems like the culprit...

And yes Pat, I want to have to rebuild lol, coz upgrades are coming very soon, so I could same some labour cost in the long run by having it built now rather than when it eats shit. I already suspect a bearing on the exhaust cam is on the way out...downside of waiting 'til she pops, is that I could make a big mess.

[Trozzle]

Mechanic suspects power steering pump. They only heard a faint sound once on first cold start, but nothing afterward.

Ah well, at least they're 99% sure there's nothing bung in the engine, which is fine in my books.

Thanks for the input nonetheless guys

[The Dan]

I don't think they'll hear it unless it's on a hill

[Trozzle]

yeah exactly - like my driveway rofl.

[Trozzle]

Bump.

OK so whether is be coincidence that it has stfu or what, my car has not made this mysterious sound once since the service.

Unless the workshop flushes the water system without telling me (which I doubt, as when there's a highish labour charge, they list everything they did), then the only thing they did that would change anything was an oil+filter change.

Other work done was replace a coilpack (as it developed a miss while they were checking it out - I don't doubt this either) and machine the discs/deglaze pads (front)

So is it coincidence that it resolved itself at the same time, or is it possible this sound had something to do with oil?