[v8volvo]

Is your SVO system a dual tank or single-tank setup? When you first changed the fuel filter, did you prefill it with *clean* DIESEL or high-quality biodiesel fuel before installing? What brand filter are you using?

It sounds like you are blending WVO straight into your main tank without any fuel system heating. With an old OM61x-powered Mercedes in warm weather you can sometimes get away with that at the kinds of percentages you are talking about, but that is not feasible over the long term in anything with the VE rotary pump system the VW IDI family (including the D24T) uses. The MB has a separate lift pump and heavy duty inline injection pump that could probably pump river mud. The VE pumps instead use an integrated lift pump and compact rotary setup, and are not happy with very high viscosities, partially coagulated fuels, high inlet restriction, etc. If your IP is full of mostly WVO, the engine is not going to start and run properly until the fuel and engine are thoroughly warmed up by some external source, or the mixed fuel is flushed out of the system and replaced with clean, regular diesel or biodiesel. Most good WVO installations in VW/Volvo diesels involve a provision that allows the fuel system to be flushed with regular diesel every time before shutdown for this reason. That is what I was asking about when I referred to "adequately flushing." If you are not using such a system and are just blending in the tank at those high percentages without any fuel heating or flushing, that is going to be problematic and lead to issues like those you are having now, not to mention negatively affecting the engine's long term health.

Your issues in this particular case are probably a combination of wrong fuel mix, air in fuel, and fuel line restriction, all of which are likely connected and originally stemming from direct WVO blending. Excessive unheated WVO % in the system will not account for the loss of prime per se, but that may have happened when you changed the fuel filter, especially if you installed the filter without prefilling it, and would in that case be an effect rather than a cause of the motor's failure to start. At the same time, if system is severely restricted at any point (which itself is a likely cause of air ingress and loss of prime and can be caused by partially congealed cold WVO), it will also not be able to build any revs or power and will act as you describe. This could be a filter plugged with congealed WVO solids (even if it is a brand-new filter!), an obstruction at the fuel line inlet in the tank either by foreign matter or solidified WVO, etc, etc. Could happen particularly easily if you recently changed your WVO source, didn't adequately filter and prep the oil, made a mistake in your math when calculating the blend %, etc... Line or filter restriction will ultimately result in air ingress and loss of prime, in addition to heavy wear on the IP.

You have introduced a lot of variables into this situation so far, the thing to do now is to try to take a systematic approach to diagnosis and rule problems out one by one, starting with the basics. Don't assume any major components (especially the IP!!) are faulty until you have made sure all the external factors are in order. Your fuel system *must* meet the following three criteria at this point to be able to run your cold engine properly:
1) Injection pump, lines, and injectors full of clean, straight DIESEL or BIODIESEL fuel -- no WVO whatsoever. That means 0%! If the rest of your fuel system is full of WVO mix, you need to either get all of that out of there, or temporarily run the engine off an external jug to get it going.
2) No air in fuel system. Check fuel line connections, hose condition, filter installation, etc.
3) No blockages in fuel system: clean, high-quality fuel filter filled with appropriate fuel, lines clear and flowing freely, no obstructions at tank inlet.

Once you have these things established and the fuel system bled, see if it will start and run OK. If it does, you know where your problem is. My guess is that your IP is OK and your motor will run just as well as it did before once you deal with any restrictions, get some proper fuel to it, and get all the air out. :-)