Ive been having some problems with my temperature lately it started with my thermostat going out so i replaced it and also replaced my radiator cap because the gasket was cracked under the lid. anyways since than ive been filling up my radiator with water every other day and the only place i can notice it leaking from is the overflow tank but it doesnt seem like alot, but it always seems really full when i look at it. can bad overflow tank caps cause overheating?

 

No, the cap on the overflow is only to allow air to vent without having an opening for coolant to splash out easily.

If you have straight (or mostly) water that you are using for coolant that can cause an overheating issue. Straight water will boil over. Properly mixed anti-freeze will raise the boiling point. A 50/50 mix is usually best. Also anti-freeze has lubricating and anti-rusting properties that are required to keep your entire cooling system from breaking down. I would start by using a 50/50 mix.

If your new radiator cap is not the correct pressure or the wrong one you can have over-heating issues. As the coolant pressure rises so does the boiling point. If it isn't allowed to build enough pressure it can overheat.

 

I doubt the fact that you're adding water instead of a proper 50/50 mixture is the reason why you're overheating. My '90 RS 305 used to overheat really bad until i replaced the fan motor and just switch on the "ac" (that doesn't work) and gets the fan going, haven't had an overheating problem since, and all i ever use to fill it or top it off is water, made it 700 miles from LA to Oakland California with probably a 75:25 or 85:15 coolant:water ratio