I9'm having a bit of a problem with the cooling system in my car in short, it over-heats but here's how. all's fine for about the first half hour to 45 minutes. then suddenly the temperature will start to creep up to hot, stay there for about 30 seconds and drop back to normal. this cycle will continue until I shut the engine off for about an hour. upon starting the entire cycle repeats. I've installed a new radiator,and a new thermostat.
Now here's the funny part, if I shut the engine down for five minutes or there about. the temperature goes back to normal, and the overheats again in about five minutes. the cooling fans don't seem to be working overly hard, and in fact seem to go off sooner than I would expect in an overheat condition.

So what am I seeing? I suspect it's something simple but I'm so frustrated that I can't see it I would really appreciate some insight into this. The weather is getting warmer and i have a 30 mile commute one way in traffic. I'm considering removing the thermostat, but I thought I'd get some feedback first. Any help anyone can offer will be appreciated

Thanks

Flush the system and remove all air bubbles with multiple 'burping' sessions (mostly this). Verify radiator fan operation, should have two speeds. I strongly suspect you have air pockets. Be careful not to get burnt when messing with radiator cap on and off stuff. I had a boil over explosion once! Scary and messy. No burns, lucky me.

Well I believe I have successfully exorcised my demons. Apparently there was a massive air bubble in the system. I finally found a valve that vents the air from the system. it looks like a mounting bolt right above the thermostat housing. Between that and a through flush, the car is running as cool as a cucumber.
I also replaced the thermostat (overheating destroys them) made sure it was properly oriented ( there's a air valve in it) and the radiator cap. Seems that the lubricant in some stop-leak formulas can destroy new rubber seals.

So I'll give it a couple of days and see if everything holds together.

No surprises here. Sorry I forgot to mention where the air bleeder is, but you found it. I've never read or heard anything good about stop leak beyond being a band-aid to get to a shop for real repairs. I'm glad you got it up and running again with proper cooling function.

Still holding together

added footnote: used distilled water in the cooling system. Seems to have helped

Yeah, good water and proper mix of coolant will keep future contamination at bay as well as prolong the life of hoses and seals. You saved $$ by doing it yourself. Great work!

I have my father to thank. I used to watch him fix the family cars when I was a kid, I started when I was 17, I'm 60 now, do that math.