The Matra Murena has a 2.2 4-cyl Chrysler/Talbot/Simca engine (as also used in some Citroens and in the little-known Talbot Tagora). My 1983 Matra is in generally good condition, has done some 120,000 km, been regularly and routinely maintained, but has been sitting in the garage and little used over the last 3-4 years. For the past 10 years I have used Mobil 1 oil - changed at regular intervals.
Recently, on starting, there has been a "rattle" or knocking from the engine for the first few minutes. The knocking varies with engine speed (ie speeds up as the engine revs up). As the engine warms up, the noise disappears, and in regular driving the engine sounds smooth and normal all the way up to the red line.
One suggestion I've had is that the oil non-return valve may not be working properly (may have stuck) - so that when garaged the oil all drains back to the sump, and thus on starting there's no oil in the block (hence the noise) until it warms up and the pump circulates the oil.
The only other clue I've noticed is some signs of "mayonnaise" in the oil filler cap. I had attributed this to condensation, resulting from the fact that it had been sitting unused in the garage, and the engine had only occasionally been started up and run briefly. But could this be a sign of something more serious?
Comments and advice would be welcome...
br1anstorm
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Does it have an oil pressure guage? If so is it taking a while to get oil pressure up? if it is then you have an oil pump problem, or possible wear. If not then it'll be the time taken for oil to get to the cam & followers.
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The lack of an oil return valve on the filter would only cause it to rattle for a few seconds while the filter filled up and the pressure built up. If the filter is mounted facing up it doesn't make any difference anyway.
As you are using Mobil 1, it could be that the oil is too thin while the engine is cold. I'd try a good quality 15/50 or 15/40 and see if it makes any difference.
The slight mayonnaise you mention is almost certainly due to short trips. It takes a fair while for the oil to get hot (as opposed to the water which will show hot on the gauge quickly) and it's only when properly hot that any moisture present will be driven off and consumed by the crankcase ventilation system. Otherwise it'll condense out at the coolest spot which will usually be the rocker cover.
Nice car, btw, nice to see something unusual still being used.
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Thanks for comments - and kind words about a fairly rare car...
I've got an oil pressure gauge. Seems to get up to normal pressure fairly quickly (though I can't remember if it was any different in the days before I noticed the rattle).
Filter is mounted roughly horizontally (car is mid-engined so the block is mounted transversely and canted over slightly).
I need to check the service and parts manuals, but I think there's some kind of oil non-return valve deep in the bowels of the engine, or in the sump?, separate from the oil-filter, which either stops oil drain-down or ensures it's pumped up immediately on start-up.
Any other possible cause for the rattle?
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I'll bounce your question off a colleague in the morning. He is another Murena lover, (he runs the matrasport.dk website).
Kevin...
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There will be an oil pressure relief valve somewhere near the oil filter housing or oil pump when opens if the oil filter gets clogged thus allowing unfiltered oil to circulate. I had this play up on a Triumph 2500 and it caused low pressure on start-up. Replacement cured it. IIRC it relies on a spring which had weakened with age.
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Is the car firing up and starting immediately?
It maybe an idea to prevent it starting so allowing the oil to circulate whilst the starter motor cranks it for a few seconds before it fires up. Not necessarily advisable on a modern car, but how about taking the coil lead off for the first 10 secs of cranking?
--
pmh (was peter)
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Another possibility could be a leak around the exhaust manifold area. This can give a rattly knocking type noise.
As the cylinder head and exhaust warms and expands the hole seals up.
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Does it have hydraulic tappets? If so are these taking a while to prime themselves as the thin Mobil 1 drains out when the Matra is laid up for a period?
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I mentioned your problem to my colleague today.
He recommended that you ask on his matrasport forum:
www.matrasport.dk/forum/index.php
there are quite a few Matra techies who provide help there.
Other than the above, the only thing I can think of that can cause a knocking on startup that disappears after a minute or so is piston-slap.
Kevin...
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