Sometimes during the Winter when it is really cold outside (14 today with a wind chill of 3), my '98 Civic has a tough time starting. The battery has tested fine, I never have any less than 1/4 tank of gas and I always run a bottle of dry gas/gas line antifreeze during the cold months.

My question is, when I turn they key and the engine is having a hard time starting and it is taking a while to start, does continuing to try and start it do any damage to the engine?

 

Maybe the battery you have has too low of Cold Cranking Amps.
Which doesnt mean the battery is bad, but it just cant function correctly under low temperatures.

 

When the battery was tested I think the guy said it has 300(?) cold crank amps. But will the long startup process put any extra stress on the engine?

 

yes dry starts will harm your engine. You can use Lucas oil stabilizer and you WILL NEVER have dry starts again. Works wonders. A dry start is metal on metal...not good. Even know the metal isn’t hot yet it still wears. Don't confuse dry start with cold start. Every engine has dry starts unless you use something to correct the dry starts. I ALL WAYS use Lucas with every oil change...it has been a huge help...especially with engines that have more that 100k on them.

But like said ^^^^ cranking amps might need to be upped to stop your cold start. Iv never had the issue since I live in FL. It gets cold at times (in the 20's)
What you should do is turn you key let it sit for 20-30 sec try and start for about 5 sec. if it doesn’t start let off...and repeat. Keeps the ware down on the cyl walls and rings.

 

You could also run 0W30 Mobil 1 synthetic oil like I do. I also got an engine block heater from the stealership.

 

I'm almost positive that my problem is cold start, not so much dry starts. I also think that even though my battery is in great shape that it could be part of my problem. This morning at 6:30 when I left my house it was in the single digits and when I tried to start my Civic, it was turning really slowly, but it took half as long to start today than it did yesterday.

 

full synthetic oil is a wast of money. Unless you really need it. Also it's thin oil and will creat more of a dry start then a reg. oil. More dry starts you have the mre ware on the engine.
As for the block heater...would not be a bad idea