I was under the SE today and noticed that the previous owner had put a fitting in the oil cooler lines, bypassing the cooler. Will that have a damaging effect on the car in the long run? Now I have to find a cooler. When I brought the car home I thought the lines were leaking I guess that was oil dripping out of the cooler.

 

It could cause the car to overheat more easily.

 

Yes it will damage the engine. The oil is responsible for approx 1/3 of the cooling of the engine. Fix it ASAP. Sorry to be the bearer of bad news BTW.