When winterizing I checked the antifreeze and it was only good to 15 degrees..Prestone dexcool.

Its still pink in color but it must of got duluted down with lake water which means my heat exchanger is probably cracked.

I drained a gallon out and poured straight antifreeze in for the winter.

Is there anything else that would cause this?

What was the antifreeze's temperature freeze rating the last time you checked it before this and how long ago?

Last year, when I winterized it was good for below zero..Ive had a bad heat exchanger before and all the fluid in the resevoir was lake water..This is still the color of antifreeze.