Having problems keeping flame burning in furnace.Oil furace hadn't been used in 2 years and had oil delivered recently.We figured the tank would be close to empty but were told after it was filled that it was already over 1/3 full. Furnace would light up with yellow flame but then turn blue and then safety kicked in. The furnace is making loud rumbling noises off and on but can't keep furnace going long enough to figure out anything.We've replaced nozzle,transformer,oil filter, cad cell and tested pump pressure so now we're wondering if the oil was bad from sitting in the tank for 2 years. Oil seemed a little on the thin side as well.Any Suggestions?

I would take a look at the limit switches/temperature sensors. They are around the heat exchanger. The furnace is wired to shut off if the blower doesn't come on or if it overheats. A false signal from a dirty or failed sensor can shut down a properly working furnace. Does the blower come on?

Having problems keeping flame burning in furnace.Oil furace hadn't been used in 2 years and had oil delivered recently.We figured the tank would be close to empty but were told after it was filled that it was already over 1/3 full. Furnace would light up with yellow flame but then turn blue and then safety kicked in. The furnace is making loud rumbling noises off and on but can't keep furnace going long enough to figure out anything.We've replaced nozzle,transformer,oil filter, cad cell and tested pump pressure so now we're wondering if the oil was bad from sitting in the tank for 2 years. Oil seemed a little on the thin side as well.Any Suggestions?
I may be wrong but doesn't the burner have to heat up the heat exchanger for the blower to kick in? The flame doesn't seem to stay going longer than 10 seconds. The furnace is an older Intertherm if that helps.

OK, there is a sensor that shuts off the oil if it doesn't detect flame. It will be right where the flame is.

So why would the flame keep dying out after only 10 seconds or so?

This is a safeguard. If the oil doesn't ignite, you don't want it to continue to spray into the furnace. This thread describes how the flame sensors work, which may help you find it and the problem.
https://www.askmehelpdesk.com/heating-air-conditioning/flame-sensor-questions-39464.html

If the flame sesor doesn't give a flame detected signal soon after the fuel comes on, the furnace shuts the fuel off quick before anything goes kaboom.

You said you replaced the cad cell. (That is the flame sensor). Fuel oil is organic and bacteria and the like can grow in it, usually making it sludgy not too viscous. Are you shure the oil pressure stayed up where it needs to be? Sometimes the king coupling can be partly stripped out and start slipping. Also did you use the right nozzle, if you went off the old one it could have been wrong. Whoever you bought the parts off can look up the model number of the furnace to be sure, also give him the burner number. Hope this helps

Having problems keeping flame burning in furnace.Oil furace hadn't been used in 2 years and had oil delivered recently.We figured the tank would be close to empty but were told after it was filled that it was already over 1/3 full. Furnace would light up with yellow flame but then turn blue and then safety kicked in. The furnace is making loud rumbling noises off and on but can't keep furnace going long enough to figure out anything.We've replaced nozzle,transformer,oil filter, cad cell and tested pump pressure so now we're wondering if the oil was bad from sitting in the tank for 2 years. Oil seemed a little on the thin side as well.Any Suggestions?
I am not an oil expert, but did experience a similar problem. In my case there was no combustion air as I had sealed all the windows and doors. You could see soot building up on the joints of the exhaust. Once I supplied fresh air to the mechanical room all my problems stopped

Pump pressure stayed at 100 so it's not the pump,transformer has good arc, correct (new)nozzle for furnace. Coupler is fine. For some reason flame does not stay longer than 10 seconds.Any other suggestions?

Even if the new flame sensor is working and sending the signal it should, it could be getting lost in the controls, either a bad control board, or a bad relay. Can you locate anything that clicks when the flame goes off?

Are you sure the primary air dampers on the combustion blower are open. If the flame seams to light good it should stay on. Do you have to reset the relay each time? Is the bottom of the heat exchanger full of oil?