Loud Knocking Engine
 

Vehicle is a 1987 560 SEL with 169000 miles. New timing chain, timing chain tensioner, and top three guide rails at 167000 miles (6 months ago).

While driving home from a short 5 mile trip I noticed the coolant temperature was up close to 100 degrees, so I stopped and topped off coolant reservoir with about 20 ounces of water. Now driving at 45 mph I notice the coolant temp rise up past 120 deg (red zone) in less then a mile. I drove another ½ mile to my house and let it idle, turned heater on high, opened the hood, and went to get some water. Took me 3-5 minutes to get some water and now the engine is making a LOUD KNOCKING noise.

It’s hard to pin point the exact location of the KNOCKING sound, but I’m 95% sure it’s coming from the engine on passenger side. I removed the passenger side cam/valve cover and everything looked normal, so I pulled the spark plugs and the plug closest to the firewall is wet and doesn’t look like it‘s been firing.

Does anybody know what the KNOCKING noise might be or have any suggestions on what I should do?

How's the oil? Any metal particles in it?

See any coolant leaks? (check radiator and water pump too)

Once it is cooled down, does it still knock?

Larry,

The oil needed to be changed, so I changed the oil and oil filter, but engine is still making knocking sound. I didn't check oil for metal before I took it to autozone.

Their is no coolant in the oil and no oil in coolant.

Yes, engine still knocks with cool engine.

Thanks for repling!

Years ago, a customer brought in a 380SE with a knock. I traced the noise down to the block, and pulled the right side head. It took me a while to find that #8 piston was not moving all the way up in the cylinder. The intake manifold gasket had broken and allowed coolant to enter the cylinder causing a hydraulic lock that bent the connecting rod. The knock was the piston kissing the crankshaft at the bottom of the stroke.

He ran the car very hot
could have compromised the engine
8 is a end cylinder
leastr on mine

the gasket could be a result

or it could have precipitated the drop in coolant therby raising the engine temp
further increasing the gasket damage.

Gasket should have been in pretty good condiiton
considering it had or should have been replaced when they did the timing chain.
Perhhaps that gasket has been a problem since the job????

Car had only had 2000 miles since the job

Most likely the overheating is a symptom not a cause
Knocking well...I won;t guess
as I never stayed in a Holiday Inn...

:freak:
Good Luck

I know how frusstrating it can be

Chas H,

Thanks for the information.

CamelotShadow,

Cylinder #4 had the wet plug

Only the Cam/Valve cover gaskets were replaced when I did the timing chain. Head gasket wasn't removed because I didn't replace the lower guides, just top ones.

Why or What would cause the coolant temperature to go from 100 to 130 degrees in less then a minute while driving 45 mph with outside air temp of 70 degrees?

Vehicle was runnung good before engine got hot and started knocking.

Thanks,

Justin

I decided to check the hydraulic valve clearance compensating elements (05-211) since I had cam/valve covers off. While checking each compenstor I was able to push down the compensator for the exhaust valve at cylinder #4 and now it is stuck down and the rocker arm is loose. The manual say's to replace any compensator that can be pushed down faster then the others.

Could this be causing the loud KNOCKING noise?

How do I get compensator unstuck? Can I turn engine over with the rocker arm being so loose?

Is the "hydraulic valve clearance compensating element" the same or another name for the "Cam Follower", "Hydraulic Lifter", or "Hydraulic Ball Stud Assembly"?

Sounds like a lifter.

Did you ever get a resolution to this problem ?

This sounds very similar to a problem I am encountering on my 1987 560SL. A have an audible tapping noise, the spark plug in cyl. #4 is fouled...all others are OK.

Briandownunder,

Loud knocking noise was from a bad hydraulic valve clearance compensating element (ball stud or lifter).

Justin