BenzWorld Junior Member
Date registered: Feb 2011
Vehicle: 1969 W114 250 /8
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w114 loud knock from motor when cold, above 20 mph
Thanks for any thoughts & suggestions, this one will be hard to reproduce for the mechanic given the temperature correlation.
1969 w114 (250 / 8), standard i-6 with the two Zeniths.
As the season has grown colder each morning, I have noticed a repetitive noise, I'd say best described as a knocking, coming from the engine compartment only at speeds above 20 mph and thereafter proportional in frequency to engine revolutions. This noise, until now, has been quiet enough to be concerning but only mildly so, because it goes away completely when the motor is fully warmed up (runs at around 160-175 F). I never noticed it during the summer months, even with the engine cold.
My morning ritual is as follows. I start the engine with pre-crank pump of the throttle, and allow the chokes to get the engine speed up before revving the engine down to a low idle. Takes it about 60-120 seconds. Always starts right up and idles very smoothly.
By the time I am taking off, the temp gauge is just starting to come off the low peg at 100F. During this time until it hit operating temp, I've recently heard the knock, but very low, and only until it warmed all the way up.
Lately it's been much colder, this AM was 30 F outside. (This is cold for California!) I started her up, she ran well and as usual through the warmup procedure. But once I hit 20 on my street, the same knock occurred except much louder this time, really disconcertingly loud. I immediately turned around and parked her back at home. The car was truly cold, as it had been about 4 days since she was last driven.
Would really like to hear thoughts on what the cause of this symptom could be. I have no other issues with the motor or drive system at all.
1969 W114 250 /8