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1980 Mercedes 300 TD

My Mercedes loses power after a random amount of time - sometimes after 30 minutes, sometimes after an hour. Any ideas?

Have you changed the fuel filter lately?

Definitely change the fuel filters first. There are three of them, an in-line pre-filter and a spin on main filter under the hood, and a strainer pre-filter in the fuel tank.
Make sure your fuel tank isn’t infested with algae. This comes from contaminated or stale fuel. This will re-clog the new filters, so fix that first if it’s a problem.

The 123 chassis diesel Mercedes were prone to liking freash air filters as well. A plugged one will slug up performance.

Next check the fuel throttle linkage. Your car has an ingenious system of very robust ball and socket connections. When these get sticky from non-lubrication the car will act like it’s losing power. Simply pop the ball out of the socket and lube with a drop of transmission fluid, then replace.

If the EGR hose hasn’t been blocked it can plug up the turbo. These cars will seem quite sluggish without an properly operating turbocharger.