C3 Ticking noise and strange oil pressure drop

[Mark P.]

I am not sure if the following symptoms have anything to do with each other.
1. Sometimes I have a ticking noise in the engine. The last time was today after driving home from Frankfurt after driving about 1 hour at 65 to 70 mph and around 3000 rpm. I disengaged the clutch and rolled to the next exit in 500 meters. When I stopped there the noise disappeared and I could make it home just as if nothing had happened. I had this problem before but I thought it had something to do with my leaking exhaust manifold. The noise sounds like a leaking manifold, just louder than it did normally. Now that I fixed the exhaust manifold it happened again. The noise sounds like metal hitting somewhere and was related with the engine revolutions. From its frequency it sounded like one cylinder was affected. I had a similar situation before and the noise always disappeared after running the engine some time at idle. I nver could find out what it is....
2. The other problem is a sudden oil pressure drop while driving on the Autobahn at 60 to 70 mph for a longer time on a quite level road. When I get off the gas pedal the pressure returns back to normal. It does not seem to be related to the oil level. I did change the oil pump last year when I changed the timing gear and had the oil pan off anyway. I did not have this problem last year. I did run another oil last year (10 W 40) and changed back to 15 W 40 this year.

What the two problems have in common: They do not appear on small roads where I do not drive with constant speed for a longer time. I can drive for days through the forests without experiencing these problems.

I hope you understand what I am trying to describe and can give me some hint what I should check.

[Craig S.]

Re: C3 Ticking noise and strange oil pressure drop

Mark - it sounds like you are experiencing intermittent loss of oil pressure due to a problem with your oil pump. The metallic hammering is probably your hydraulic lifters starving for oil, and collapsing and hammering on the cam and valve stems/pushrods. When the pressure returns, the lifters pump back up and function correctly. I would immediately pull the oil pan and diagnose what is going on with your oil pump. Possibly there is a problem with the bypass spring, or the pickup. It almost sounds like there are instances of oil starvation or caviataion....Craig

[Duke W.]

Re: C3 Ticking noise and strange oil pressure drop

Give us some gage readings. What the the oil pressure normally run, and what does it drop to when you notice the reduction?

Duke

[Mark P.]

Re: C3 Ticking noise and strange oil pressure drop

The oil pressure in normal run is about 50psi, it suddenly drops to about 35psi. The oil pressure at idle with engine warm is about 25 to 30 psi. The oil pressure did not drop yesterday when the ticking noise appeared.

[Duke W.]

Re: C3 Ticking noise and strange oil pressure drop

A couple of thoughts. First, it's not clear that the noise and oil pressure drop are correlated. You didn't mention the year, but I've seen oil pressure fluctuations from flakey sending units, and I think the later Sharks have an electic gage rather than a mechanical bourdon tube gage like the Midyears. If you do have a electric gage with a sending unit, replace the sending unit. They are not very expensive. A clogged oil filter could also cause a drop in pressure, but it's rare for oil filters to clog if they are changed at least every other oil change unless something inside the engine is disintegrating. Next time you change the filter check that the bypass valve is properly seated and look for visible particles inside the filter boss, the filter, and the drained oil - maybe sweep the drained oil with a magnet to see if you can pick up any particles.

Intermittent ticking can be caused by a couple of problems that I can think of. The most common is a "sticky lifter", so you might want to try a can or Bardahl or some other product that claims to free sticky lifters. Basically they're all just a can of mineral oil with a heavy dose of detergents, but for the five bucks it'll cost you it might be worth a shot.

Another problem that can cause intermittent ticking is a scuffed piston/cylinder. In the early stages the ticking is usually most noticeable when the engine is cold and will go away when the engine warms up. As the scuffing gets worse the noise eventually is there all the time and will change from a ticking to a knocking sound, but it may take a long time for it to get noticeably worse.

Oil pumps are simple and about as reliable at the morning sunrise. I don't think I've ever heard of a bonafide oil pump failure on an unmodified production engine,

Duke

[Mark P.]

Re: C3 Ticking noise and strange oil pressure drop

Sorry I forgot to mention: It's a '69 L46 and has the bourdon tube gauge like the midyear. So I can exclude a sender problem.

[Jack H.]

Saw a real 'funny' once....

Car made 'tinkling' sound as if it had bad fuel and was knocking.... Sound came and went rather randomly.

Finally the jury came in.... NOT GOOD! The crank timing gear was a factory escape that missed being hardened. As timing chain ran, it ate into the gap between gear teeth causing the gear to 'shrink'....

The tinkling sound was slack in the timing chain randomly hitting the inside of the timing cover. Eventually, the gear wore to the point the timing chain jumped teeth. Valves kissed pistons, push rods turned to pretzels, one cylinder head cracked and during disassembly/rebuild the strange truth was finally learned.