I have 1989 Chevy Caprice Wagon. Can someone will knows the size of the oil drain plug ? And is synthetic oil will be OK, or I have to stick with the normal oil. Greatly appreciated for your help.
Synthetic oil is simply the usual fossil fuel engine oil further processed for more favorable molecular structure. It wouldn't hurt to use it. I simply don't, because I don't drive frequent enough for meritting timely oil changes. I've used synthetic manual transmission oil before and have noticed an improvement in shifting with not the newest of synchronizer rings
I don't know the diameter, you will have to actually measure it, but that'll give you the chance to let your engine drain a bit more while you go get a new plug and/or seal. This SAE fastener chart section tells you what coarse and fine thread sizes go with what diameter bolt. I suggest you only get the new plug from an auto parts store; regular bolts are not suited to sealing a drain hole. As for syn oil, unless your engine leaks like a sieve, it's not a problem to use it.
Doghead and Silvertwinkiehobo many thanks for your very knowledgeable answer. I greatly appreciate your support, it help me a lot.
Why synthetic oil is often worth its extra expense: https://www.shenzoracingoil.com/smartblog/3_which-engine-oil-is-right-for-you.html
