Ive got a windshield covered in sap, paint dust from sanding and other crud that's really fused itself good. Windex aint cuttin it

I have laquer thinner, acetone, mineral spirits and denatured alcohol. Im sure most of them will cut through everything on the windshield with ease, Im just not sure if any of them might damage/fog the glass.

Which should I use?

Any of the chemicals you mentioned will work and shouldn't hurt the glass. I've used lacquer thinner myself on my windshield (outside) to get various crap off of it and it never fogged the glass.

When I pulled my old rear glass I SOAKED it in lacquer thinner and scrubbed to get all that old sealer off the edges and the glass is fine.

If you are still scared, try 50/50 ammonia/water mix which is basically Windex on steroids. Wear gloves for that...

I think you will be fine.

When I used to work out in the shop running a wood saw, I would get tree sap on my hands all the time. The only thing that would remove it was WD-40.

Hands down the best stuff I've ever used:

http://www.glazedistributing.com/glaze.html

Last item on the page. I have a 70' blue spruce in my front yard and always have to clean sap. This wipes it right off like it's not even there.

I've heard Pine Sol takes off sap.

I have used lacquer thinner for glass. Cleans well with minimum abrasion and does not hurt the glass. Just be very careful as it will hurt surrounding paint, plastic or rubber. I keep the can well away from the car and just wet the corner of a rag... do a small area at a time.

bar keepers friend

lacquer thinner

Keep it off the paint.

razor blades work well for me.

Like dissolves like. So, for tree sap, you want a pine terpene or an orange terpene. Pine Sol is one, Goof Off is d-limonene (from oranges). Neother will hurt paint and both are relatively safe on your hands. PineSol will rinse with water and the Goof Off you could use some good detergent afterwards. ( I cleaned defense products for 35 years so I know some good cleaning stuff. :).
Tom

Use a non-scratching pot scrubber/sponge to scrub with.

Fast Orange hand cleaner. I had some 30 year old crud on a back window that nothing would remove not even thinners. The local glass shop told me to use this trick it worked great.

FAst Orange has some d-limonene (orange terpene) and it makes good sense it would work well too. Thanks for the tip!

Doesn't fast orange also have grit in it? I'd worry about scratching or fogging the glass.

I've used WD-40 with good success.