As many know, the weak spot on the L36 is not actually the LIM gaskets, but the UIM itself. Correct, not even the UIM gasket. Got a chance to document this issue recently and wanted to share so that L36 owners realized why it is suggested that they change the UIM or plug the coolant ports leading out of the LIM.
Typical L36 , UIM is black plastic/nylon material
The failure is evident if the car suddenly loses about a half to full gallon of coolant and the motor hydrolocks or appears to be burning coolant.
Reason behind the half to full gallon is the LIM fills when the UIM fails
Here's the UIM upside down. The large hole is where the EGR tube passes hot gasses through the manifold. A passage that is flanked on both sides by coolant passages to the throttle body. (the two smaller holes)
Looking at the EGR area with a pick...we can usually find a crack or hole
In the early model 97-99 L36's the EGR stovepipe was much larger. When buying a new Dorman etc UIM kit, you usually will get different diameter pipes. This is to put a smaller pipe into the place of the large old pipe. No matter what you put in though..the pipe usually doesn't have enough air gap to the UIM to keep it from expanding and contracting with the heat cycles, which cracks and degrades it.
Often if you catch the issue early enough and don't beat up the bearings trying to start a hydrolocked engine too many times, you can fix the issue and save the motor.
The different sized stovepipes that you get when you buy a new UIM kit.