We have a 1980 300TD wagon (non-turbo) that we recently converted to run on veggie oil. We were driving it to Colorado Springs from Berkeley, CA and everything was running smoothly until outside salt lake city in the heat of the Day. Going up a steep pass on a highway with no shoulder, something happened to the cooling system and steam starting pulsating out of the engine compartment. There was a loud screeching, squealing noise which we attributed to the steam coming out of the radiator. We pulled over as it was safe about (20 seconds) later and checked the radiator which was boiling and had lost a lot of water. We let the car cool, added water and continued on, adding water every half mile to get over the pass.
When we checked the oil later that day, it was down a quart which was a lot more than it was burning before. We started to notice blueish clouds coming out of the tailpipe when we started the car up.
In the cool of the evening, without climbing the heating problem seems to have stabilized.
Nearing the end of our trip the engine lost almost all power (15mph on the highway) and it seemed as though not all cylinders were firing (could be a veggie oil, air in the fuel line problem).
There is also a new quiet knocking noise at low rpms just for a moment as we accelerate out of first gear.

We aren't using the car until we know whats wrong. Beyond the cooling system problem it seems as if we might have damaged the piston rings or something else in the engine. Its an old car we would like to fix it, does anybody have any suggestions or advice to determine where to go from here.

Recent work:
replaced vacuum pump
new transmission kit
new glow plugs
new brake booster

Thanks for any advice.

Wiley Rogers
1980 300TD - Veggie oil conversion.