I am refinishing interior doors. Everything went well at first, but then it started going on blotchy, thicker in some places than others. I think it is drying too fast and is becoming thicker. What can I do to thin the Minwax so I can get it on smoothly?

Odorless mineral spirits. You need to be very careful with polyurethane "aging" in the can. Once the polymerization begins to take place, the poly is pretty much gone. After thinning, pour it through cheesecloth or a paint filter to remove possible gel particles.

Interesting that you mentioned being careful with polyurethane "aging." This is a new can, not even opened until a week ago, and by the second coat was starting to dry too fast. At first I thought it was my fault and that I had not put it on smoothly. By the third coat it was awful with some spots looking the way semi-gloss should look and other spots looking as if it had not been covered. Now you tell me I can add mineral spirits, but have to strain it! I am so sorry I bought this product. Any product that can not be used for more than one application is surely defective. Also when I called Minwax, I was told that I should not have used foam brushes. Wonder why the can lists both foam and bristle brushes for application? I don't need a product that doesn't know itself. A very costly lesson learned.

I use the Minwax oil based poly quite often and have never had a problem. Are you sanding between coats? It has to be dry before applying another coat and it can't be worked too much. This means that once applied do not keep brushing over it. I use a small foam roller when applying it. I also find that if the door is removed and laid on top of saw horses or even flat on the ground it is much easier to apply. I have never had to thin this product.

You think you have it bad. I used Minwax super fast drying poly for about 1300 sqf of oak flooring was great until the last coat (3rd) never dried and never dried on the paint stick. Contacted Minwax they shipped about $350 of new product but claimed that they ran test for the product and batch run and have no found issue. Ran the heat up to about 90 for over 12 hours still did not dry even on the paint stick. So know I am buying chemicals to strip as I can not sand as it gums up the sand paper. Was told to contact Home Depot for compensation for clean up and redoing as the issue was after it left Minwax. Don't know what Home Depot would have or could have done to the sealed product. Again Minwax claims no issue but sent new product to replace. I offered to ship them the wet paint stick. It has been 3.5 weeks now and still is sticky both floor and stick. When I contacted Minwax at first I had already scrapped some up in the living room and areas we needed to use for living. They told me not to scrap anymore as it would dry. Well I guess I should have scrapped it all up as it is gummy but requires stripping chemicals to get it off the floor. Would love to have they fine folks behind the phone out here on site to see the REAL MESS. I will have about $200 in chemicals $20 in mineral Spirits and another rental sander $80 and $50- 100 in sanding pads.
Any better ideas would have been great.