Valve train noise/ fan problem
 

1988 MB 190e 2.3. Starting to sound like a sewing machine. What is the most likely source of the noise -- lifters, rocker arms, cam, valve guides, etc. and how do I figure it out? If it is the lifters for instance, should I replace lifters only or should I change the rocker arms as well? Is this a do it yourself job or are special tools required?

Also the magnetic fan only seems to engage with the A/C on, otherwise it does not work causing the engine to run hot--I think. I know there are some sensors somewhere but I'm not sure where and I assume these could be the source of the problem as well as bad fan. Not sure how to go about this. Thanks for any help.

Problem 1...not sure, need to see and hear engine run in person. Maybe someone else will have an idea what the problem is.

Problem 2...The fan is only operating when A/C is on because that circuit is coming from the high pressure switch on the receiver/drier. The main fan should also operate when the engine temp. reaches a certain temperature, 100 C. or 110 C. depending on which switch you have.

Test the Fans

With ignition on and engine NOT running:

At the 3 prong temp. switch behind the thermostat, the pair of contacts operate the Fan Clutch. If you short out the connector (2 wires), the fan clutch magnet should operate. If this test passes (magnet operates and you can't turn the fan by hand) and your car is overheating and the main fan is not operating, then your temp. switch is probably bad. If you feel comfortable doing this, you can leave the connector shorted and start the engine and see the main fan operating.

At the 2 prong temp. switch behind the 3 prong one, those contacts operate the aux. fan relay which then operates the aux. fans. Connector shorted...aux. fans operate. If you listen, you can hear the relay operate before the aux. fans do.

fan trouble
 

Thanks for the info SLK230red.