casasteve

Hey all. I've tried searching around and I'm looking for a more specific answer then "Yeah, it's a common thing" which seems to be the standard answer

So since winter hit last year I've had a recurring noise. On cold start, after my car has sat overnight, I get a what sounds like a knocking noise. But, it only happens for literally a couple of seconds. The noise is kinda of deep sounding but with a definite knock noise (so not really piston slap?). It only happens for 8 or so "revolutions" (sorry, not sure if that's the correct term... cranks maybe?). I get no knocking after this initial cold start noise. I think I might have a bit of piston slap, the engine isn't silky quiet but it doesn't sound bad at all (a little tapetty).

Some details:

53 plate Blobeye PPP WRX Wagon with 151K miles. Has been serviced regularly according to paperwork. I've done two oil changes since buying it, and I'm using 5w40 Shell Helix. Last oil change was about 300 miles ago. I don't believe the engine has ever been rebuilt, but cambelt etc has been done to service schedule.

I almost always warm the car up for at least 5 minutes standing still (often longer), and then off boost for at least 10 minutes, giving the oil/engine plenty of time to warm up. I run Shell VPower and have no mods (other than the factory Prodrive setup).

Someone has suggested that the 5w40 might be too light for the mileage of my engine. Is this plausible?

Thanks!

Maz

iTrader: (34)

Sounds like a bit of piston slap. Nothing to worry about if it is. You could try a thicker oil like a 10 50 and see if it makes a difference. I wouldn't sit idling for five minutes, better to move off straight away and just keep off boost till the fluids are up to temperature.

casasteve

Interesting what you say about not sitting. Would it make that much difference?

casasteve

Found a thread. Interesting reading I'll adjust my warm up routine then!

https://www.scoobynet.com/scoobynet-...ld-advice.html

Maz

iTrader: (34)

Sitting idling does nothing except waste fuel and possibly promotes carbon build up in the engine. Plus it lengthens warm up time so is effectively counter productive.

ditchmyster

iTrader: (7)

Start it drive off like you stole it, live life 10 seconds at a time.

I use Motul 300v 15/50 in my 114k miles Blob Wagon PPP, 151k is quite some going I hope mine gets there.

Maz

iTrader: (34)

Motor oils are thicker at colder temperatures. A couple of generations ago, motor oils often did not provide adequate lubrication at cold temperatures. Idling the engine after a cold start could warm up the oil and provide better lubrication before driving off and putting a load on the engine.
However, it is important to understand that both motor oils and engines are much improved today. Motor oils provide proper lubrication over a wider range of temperatures, contain additional beneficial additives, and do not deteriorate as quickly as the vehicle is driven. Engines are machined to much tighter tolerances, maintaining a consistent film of oil over all surfaces, and the internal moving parts are made out of better materials.
The result is that, except at very cold temperatures (below 0-20°F), vehicles can be driven gently after a very short initial idle period - about 5 seconds - without damaging the engine.
In fact, it is better for the engine to be driven gently after a short initial idle than to idle for longer periods of time:
• Idling is not an effective way to warm up the engine. A cold engine can require extra fuel for proper combustion, especially at temperatures below 50-60°F. This extra fuel can wash oil off of the cylinder walls, accelerating engine deterioration. Driving the vehicle greatly reduces warm-up times and the need for excess fuel. It also warms the oil up much faster than idling.
• The catalytic converter reduces engine emissions by more than 95%. However, it is ineffective at temperatures below about 600°F. Driving the vehicle will warm up the catalyst faster and reduce pollutant emissions.
• Excessive idling can damage your engine and components. An idling engine is not operating at its peak temperature, which results in more unburned fuel residue. This fuel residue can contaminate the oil and can be deposited on spark plugs and exhaust valves. Idling can also let water condense in the vehicle’s exhaust, leading to corrosion of the exhaust system.
• Idling produces zero miles per gallon. Driving off gently after a short initial idle period will reduce fuel consumption and greenhouse gas emissions.

casasteve

Thanks for the replies. A bit of an eye opener actually. I will change my routine to set off within a minute of firing up from now on (get's boring just sat there anyway!)

I may try changing to 10w50 on the next oil change as well. See if that makes any difference...

Thanks for all the replies

300gnspitzer

Piston slap doesn't stop after a few seconds, the engine needs to warm up quite a bit to reduce the bore to piston clearance. If the knocking stops when the oil light goes out its probably the big ends.