Help Identifying a kid's book series

A friend of mine is trying to figure out the name a book series he read in 5th or 6th grade (he’s 31) that he checked out from a public library. He hasn’t given us much to go on and our Google-fu is not working. I told him that the Dope never lets me down, so I’m turning to the dopers to help figure this out. Here’s what he remembers:

-they live in a normal world with elements of magic and the occult.
-the protagonist is a young boy and his parents are not in the picture
-He goes on these adventures with his grandfather.
-they try to figure out the source of these evils before it’s too late.
-the tone is quite dark for the age level.
-he read at least 6 of the books in the series
-they were chapter books between 150 and 200 pages long
-there were runes and amulets involved in some of the storylines
-In one of the books, they were driving a car and had just discovered something in some derelict location and the source of evil was chasing them and headlights were behind them and they cross a stream and the car stops chasing them before the stream. (kinda like Nazgul)
-locations they explore were like abandoned houses, cathedrals, crypts and dark forests.
-things we’ve eliminated: hardy boys, encyclopedia brown and stuff like that

Thanks for any suggestions and input!

These sound like the books by John Bellairs? I loved them when I was in grade school/middle school and I’m about the same age as your friend. One book by him, for example, is The House with a Clock in the Walls. They had neat illustrations by Edward Gorey in them. The Anthony Monday series may be what he’s thinking about in particular.

Jay Williams wrote a book called The Magic Grandfather (“An 11-year-old discovers that not only is his seemingly ne’er-do-well grandfather a bona fide sorcerer but he too may have an untapped talent for magic.”) in 1979 and was also co-author of the Danny Dunn books, about a boy who has science fiction-y adventures; could your friend be conflating them?

Wow! Got it in one! I told my sister-in-law and her boyfriend that the Dope never lets me down (her boyfriend was the one wondering which book series it was). I told them it usually only took about 10 minutes for the dope to figure it out even on the meagerest of identifying data and sure enough, the dope came through. Thanks guys!

Good job, beandog!

Yay, glad I could help! Now I kind of want to go back and re-read some of those books…

This is the Lewis Barnavelt series:

John Bellairs wrote the first three books. He left outlines for the next three books which Brad Strickland finished. Strickland then wrote six more of them. Edward Gorey illustrated some but not all of them. I thought Strickland did as good a job of continuing someone else’s series as I’ve ever seen.

I was going to suggest The Dark is Rising … although that’s not precisely a magic grandfather, now that I think on it.

Still, if you like that sort of thing, you should check that series out.

I’m glad to hear that - I loved the original books, but never tried the later ones because I figured that they would be not up to the Bellairs standard, but if they were, now I have something else fun to read.