I've got one question; I was looking over this car that I was going to buy and there was engine oil in the radiator. I asked the guys why it was in there and he said he didn't have enough coolant to fill it so he used engine oil. He topped up the radiator and topped overfill bottle with oil.
Will having a radiator full of engine oil do any damage to the motor in the long term or short term?
The seller should not be selling the vehicle with oil in the cooling system. That supposed "quick fix" should have been rectified at the earliest opportunity. Have him flush the cooling system and put another few tens of kilometers on the odometer before you even consider such a vehicle.
If the seller is topping off the radiator with oil instead of water, then he is either lying, incompetent, or was caught on the side of the road with no other options. Leaving the oil in the radiator makes each option more likely in decreasing order.
I would be more concerned about whether engine oil is actually finding its way into the radiator from the engine.
If it is, this would be indicative of a compromised head gasket, warped cylinder head, or damaged oil cooler (if the car uses radiator coolant for cooling the oil). The first two items are not trivial to replace or fix. The third one isn't far behind.
If you consider the seller's claim of topping up the overflow tank with engine oil to be legitimate, the engine itself should be fine, but the cooling system will need thorough flushing at minimum.
Yes, it's possible some of the seals designed to withstand water and glycol could get damaged
I am thinking you are creating a fictitious scenario here, so I'll roll with it.
If you filled your radiator with oil and started your car and let it run for awhile I would be most concerned with damage to seals that were designed to withstand water and glycol.
Petroleum based products could damage these seals by penetrating and degrading them. I would imagine that some manufacturers are using material that would not be effected by petroleum products and some are not.
This is assumptive on my part and I don't have any citations to back my concern.
Aside from the possibility it might damage some seals, I don't see engine oil doing damage to your cooling system by simply being in the radiator.
Strange - engine coolant is antifreeze diluted with water. So the seller is claiming he had oil but not water? I would not buy that car.
For the seller, a coolant system flush would in order, both forwards and reverse, and then refill with antifreeze and clean water. If engine oil still appears in the coolant water then the oil is moving from the oil galleries to the water galleries. Check the oil filler cap for white creamy emulsion like this
This would be water going the other way, into the oil lubrication system.
If this is the case, engine oil in the water is evidence of existing motor damage.
I consider it quite more likely that it was the engine that had been putting oil into the coolant. Of course, it may also be that the seller poured some obvious additional oil on top in order to mask the defective motor seal, a very expensive defect to fix.
Have into account two factors: oil viscosity may be much or very much higher than the antifreeze fluid (glicol-polipropylene derivates) normally used: the radiator grille has capilare-thickness tubes and an hydraulic circuit (pump, filter, reservoir...) prepared for much less viscosity. Furthermore, the oil will becoming more and more viscose while the temperature increases... until a cold night (not so cold: just under 50ยบ F) will become absolutely blocked (yes: around cylinders will regain the low viscosity state, but the radiator grille... well: I wound't like to find myself in a such situation).
As oil has a higher viscosity than water, I think it could damage the water pump because it would put more stress on it. Also, the oil would flow slower than water and this could lead to overheating of the engine.
The question I could do myself would be if that oil on radiator could'nt be the consequence of a damaged head gasket which pours oil from lubrication system to the cooling one (then, the guys could have improvised along the way any bad or worse excuse). Of course, I've purchased 4 2nd hand cars, and I would have rejected any candidate which had oid in the radiator: that means a both deffective lubrication and cooling systems. I will aquire a such car the day I feel I am too much happy.