I recently got my 2008 infinti g37 coolant pressure tested due to the fact that I always have to top off my radiator everyday.

The first shop said the car hold pressure fine just air in cooling system. After a couple days I had to top off my radiator again.

I went to a second shop and they said I have a bad head gasket because they found coolant sealant in my coolant. I do scent a faint smell of coolant in my exhaust? sometimes but no white smoke yet.

I have a coolant no spill kit to bleed my cooling system every couple days so I don't loose coolant.
My oil is not milky nor do I see oil in my coolant.
oil does turn black after a couple hundred miles and was draining like water.

Car does throw a random missfire code every other day. Also when the car is fully warm and left alone for an hour in half it starts pretty rough and a quick missfire for a couple seconds then runs normal.

I also never overheated I even raced people. that was before I knew I had a big problem.


I'm pretty sure its a internal leak, but I would like some information on what to do.

 

If you're poor, rent or borrow a cylinder leak-down gauge so you can determine which side has the leak. Then replace that offending head gasket. It would be wise to have the head checked for true.

It would be better to replace both head gaskets since you're in there. Not much extra effort involved.