The other day after about 2 hours of freeway driving my car started to "lose power". After letting it set for a while the problem was completely gone.

Then today after about 40 minutes of driving home from work I started to get the same symptom. When I got home I left the car running and I could see that the small secondary filter had a lot of air bubbles in it. When I would give it a bunch of gas and get it up to like 3,000 rpm the engine would die when I let up off the gas.

I found the part number for the in tank strainer but now I seemed to have lost it. I thought I would start by replacing that and checking the fittings. But since this seems to happen primarily when the car is warmed up is there something else I should be checking?

By the way after the road trip I did fill up the tank, it is a bit more than 3/4 full right now.

It is a 1987 300TD Wagon with the OM603.

First take care of the air intrusion (new hoses from fuel lines to filters) most likely your problem, then if you suspect tank filter blockage try some Startron additive to dissolve/klll
cooties in your tank.

Sounds like when something expands with warmth, it lets air in.

How's your primary filter look? Those lift pumps mean BUSINESS, I've had them suck air past hose clamps when the primary filter gets clogged. Maybe enough running/sustained fuel use clogs the filter enough to have it start sucking air, and when you stop then the suction is released and sediment falls away from the element.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Your description is consistant with a possible blockage of the fuel tank vent as well. As vacuum builds up in the tank the lift pump has greater and greater difficulty in getting solid fuel. Remove or loosen the fuel tank cap as a test. Or when this occurs you do not want to hear a large noise of the air entering the fuel tank as you remove the fuel cap. The car siting allowing the vacuum to be reduced by a little air intrusion with time is reasonable.

Of course this could be other things. Still from your description I would tend to check this out first. Not that uncommon on these cars.

So far I have replaced the filters. I happened to have a set on hand. That seems to have stopped the problem for now. I will most likely replace the strainer soon anyway. I am not sure the last time it was done.

Thanks you for the help. If the problem occurs again I will post here.