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 Post subject: 220000 mile 944 NA with knocking noise
PostPosted: Thu Jan 31, 2019 8:47 pm 
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Joined: Sat Nov 14, 2015 12:06 pm
Posts: 24
Model: 944
This is my daily driver taking me regularly to Germany where I work (I live in Southampton)
Got the car 7 years ago and have done 82000 miles since with perfect reliability.
Gets serviced every year and uses Mobil 1 Motorsport oil
My regular journeys at the moment are Southampton to Heathrow on a Monday and back on a Friday.

A couple of weeks ago a knocking started from the engine (definitely engine related) at higher speeds (above 3000rpm) when slightly accelerating: the noise disappeared (or was much quieter) when I backed off the throttle: the car idles perfectly and runs without noise or vibration at lower speed

My initial thought was big end bearings (oil pressure is always rock steady at 4.5-5 Bar when running): they've not been changed during my ownership.

Sent an oil sample off to Millers for analysis which shows signs of Boron and Sodium which is linked to water in the oil, ie head gasket failure. (there are no visible signs of sludge in the filler cap and the water expansion tank looks clean)

I will make compression test this weekend.

Question: has anyone seen or heard of a knocking noise with a blown head gasket? There are no visible water bubbles in the oil and the car is not using any water/coolant

Thanks for any advice


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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Thu Jan 31, 2019 10:15 pm 
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Joined: Wed Sep 08, 2010 8:44 pm
Posts: 8912
Location: Birkenhead (UK)
Model: 924 na
If there are no signs of "knocking" at idle/low revs then its unlikely its bearing related.

If you have no sludge, especially at time of year, you are unlikely to have a head gasket coolant leak but check your coolant system is pressurising.

Wild guesses (bearing in mind that I can never tell what direction sounds are coming from and have front/back of car wrong on some occasions).

Loose spark plug.
Exhaust rattle.
Heat shields.
Alternator mounts.
Airbox/fuel distributor mounts
Wheel nuts.
Water pump.
Battery clamp.
Engine mounts.
Gearbox mounts.
CVs.

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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Fri Feb 01, 2019 5:55 pm 
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Joined: Sat Dec 01, 2007 1:31 pm
Posts: 19955
Location: Lurking in Preston
Model: 924 Turbo S2
What he said.

Knocking from bearings would most likely be while the oil pressure is low at idle and get worse as the oil pressure falls as it warms up.

NA head gaskets blow from cylinder to water jacket. The oil passage is a substantial copper ring, I don't think I've ever seen one blow.

What is hot oil pressure?

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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Fri Feb 01, 2019 7:03 pm 
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Joined: Sat Nov 14, 2015 12:06 pm
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Model: 944
Thanks for the comments: hot oil pressure is 4.5-5 Bar all the way from tickover to full speed: maybe 4 Bar at idle in temperatures seen last summer in Germany (high 30's)

The noise is definitely engine speed related as when I dip the clutch and let the engine fall back to idle speed, the noise stops.

The engine oil pressure (the sender was replaced a couple of years ago with a new Porsche part) is good.

I have not used the car since the noise as I want to be sure im not going to do any serious damage.


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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Fri Feb 01, 2019 7:42 pm 
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Joined: Sat Jan 30, 2010 11:13 pm
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Location: Somerset
Model: TheOnly Way Is Turbo
When my big end bearing went it was knocking on acceleration and maintaining speed. Backing off the throttle there was no noise at all as it coasted in gear. Once I pulled off the motorway and parked up idling in the services car park it was fine. Revving it made it knock. It was pretty obvious it was an internal engine issue.......so try and rev it and see if knock returns. It may rule out or not non engine items

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1980 924 Turbo Series 1 - Alpine White & Guards Red
Omega forged pistons, lightened and balanced bottom end, ARP studs + Cometic MLS HG, Piper fast road cam, K27/26 3257 hybrid turbo, 951 ducted FMIC, Custom intake manifold, Mittelmotor dizzy & cam pulley, Adj boost - dyno’d at 225bhp @ 1.0bar on previous CGT turbo, Engine datalogged and on boost fuel enrichment managed with Zeitronix ZT2 & Phormula KS4 knock sensor, 944 turbo all alloy radiator, Hayward & Scott custom tapered race exhaust, GAZ Gold coilovers, Fuch'ed up, Quaife LSD
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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Fri Feb 01, 2019 8:16 pm 
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Joined: Sat Nov 14, 2015 12:06 pm
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Model: 944
Thanks, your symptoms pretty much sum up what I have: the knocking was at first only on acceleration, but last time I used the car it seemed to knock at 60mph, then 50mph.........

I have the parts now, so will probably make the change anyway.

I will make a compression test and coolant system pressure test just to rule out the head gasket.

Work has to be done outside, so there no rush with the weather the way it is at the moment!

Will keep you updated


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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Sat Feb 02, 2019 9:55 pm 
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Joined: Sat Nov 24, 2007 7:05 pm
Posts: 3855
Location: Townsville, Australia
Model: 1984 NA
My HG blew between 3 - 4 so it was pumping back and forth and sounded like a main bearing went. no oil pressure loss or bubbles in coolant.

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 Post subject: Re: 220000 mile 944 NA with knocking noise
PostPosted: Sun Feb 03, 2019 12:12 pm 
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Joined: Sat Nov 14, 2015 12:06 pm
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Model: 944
Thanks for that: i'll check it when I make the compression test


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